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Automatic update security

Bitvise software supports built-in updates. Checks for updates are enabled by default, and can be disabled. The built-in update process includes security checks:

The version information received during an update check is digitally signed. This signature uses a private key separate from TLS.
New version information includes a SHA-512 hash of the new version installer. This hash is covered by the digital signature.
The update process verifies that the cryptographic hash of a downloaded installer matches the expected value.
Configurable update settings include an Update stability delay. When a new version becomes available, the software will not automatically update until it has observed the new version for the configured number of days. This setting is enabled by default, and can help users avoid updates to new versions in case issues are found soon after release.

Upgrade access

For Bitvise SSH Server, updates to new versions require a license which is up to date with upgrade access. The latest activation code must also be applied, and is not updated automatically. If you have purchased per-installation licenses, you can check your license status, extend upgrade access and obtain your latest activation information in your License Overview.

To check license status for large-scale licenses, contact Bitvise. If you are using a reseller, resellers can place orders and extend upgrade access, but can only provide second-hand information for license status inquiries.

Bitvise SSH Server Version History

For issues that might arise using the latest SSH Server versions, see Known issues.

Changes in Bitvise SSH Server 9.68: [ 9 November 2026 ]

Security updates:
- This version fixes multiple security issues, including SSH protocol and key handling, excessive resource use, and failures to enforce configured access restrictions. Depending on server settings, some issues can affect unauthenticated connections. We recommend upgrading.
Compatibility:
- The SSH Server now requires at least Windows Vista, Windows Server 2008, or newer. Windows XP and Windows Server 2003 are no longer supported.
- The SSH Server's settings format has changed. Settings saved by versions 9.67 and newer cannot be loaded by earlier versions. Applications that use the scriptable settings COM object using static linkage will need to use the new 9.67 interfaces. Scripts that use dynamic languages, including PowerShell, retain 9.xx compatibility.
- Remote administration now requires WRC version 9.67. This is included with Bitvise SSH Client 9.67.
SSH cryptography:
- Bitvise software now supports hybrid post-quantum and classical signatures using MLDSA44_Ed25519 (ssh-mldsa44-ed25519). This combines ML-DSA-44 and Ed25519 for server and client authentication. The algorithm is only available when FIPS 140 cryptography mode is not enabled in Windows.
  
  New installations now generate RSA-3072 and MLDSA44_Ed25519 host keys by default. If Windows FIPS mode is enabled, the defaults remain RSA-3072 and ECDSA/nistp384. An upgrade does not change host keys for existing installations.
  
  If considering whether to generate a new MLDSA44_Ed25519 host key on an existing installation, review Host Keys in the SSH Server Users' Guide. Specifically, the section: Adding a host key with a different algorithm.
- SSH compression using zlib is now disabled by default in new settings. Upgrading preserves the existing setting.
  
  The concern with zlib is that it uses a shared compression dictionary for all connection channels. If channels contain data from different users, for example when using port forwarding, a user of one channel may be able to leverage compression characteristics to discover data sent on other channels in the same SSH connection.
  
  Per-channel compression could avoid this issue, but needs a specification. Bitvise would consider this if another SSH implementation has interest.
- SSH algorithm settings now support configurable preference order. The new Algorithm preference setting allows compatible clients to use the SSH Server's configured algorithm preference, instead of the client preference. This is initially intended for master/follower synchronization. The implementation follows the Internet-Draft Server-Led Algorithm Preference in the Secure Shell (SSH) Protocol.
  
  By default, server algorithm preference is offered by SSH Server instances configured as Master or Secondary master. It allows a master to choose algorithm preference for follower synchronization connections. Clients that do not negotiate this feature continue to use client preference.
  
  Like other clients, Bitvise SSH Client and FlowSsh do not implement this feature at this time. They continue to negotiate client preference.
- Further limited the amount of CPU that clients can consume through repeated SSH key exchanges.
Control Panel and Settings:
- The Connections tab now provides more detailed transfer statistics, including connection totals, FTP data transfers, and transfer speeds. Improved responsiveness when displaying many connections.
- Improved handling of overlapping settings windows and background notifications. Fixed cases where notifications could appear in the wrong window, fail to complete an action, or cause an internal error.
- Fixed Easy settings issues affecting the saving and copying of accounts. These included discarded changes to file-share passwords and unintended changes to inherited permissions.
- Windows account and group settings entries can now be marked Ignored. This retains their configuration while excluding the entries from account matching and settings inheritance. It also avoids lookup warnings for retained entries referring to removed Windows accounts or groups.
- Added a global Allow public key management setting under Access control. Groups and accounts can inherit this setting or override it. Existing permissions are preserved during upgrade.
- Easy settings no longer offers unrestricted shell access for virtual accounts. This remains configurable in Advanced settings, with a warning about the lack of isolation between virtual accounts that use the same Windows account.
- Fixed SSH Server Control Panel startup errors associated with acquiring the system tray icon, including during Windows login.
Authentication and virtual accounts:
- Fixed security issues in the handling of TOTP grace periods.
- Virtual accounts configured to share a logon session with their group now consistently use the group's Windows security context. A stored account-level override could previously apply despite group sharing being enabled.
- Improved protection of SSH Server subsystems against interference between virtual accounts. Virtual accounts using the same Windows account still do not provide the isolation of separate Windows accounts when users are allowed to run arbitrary programs.
- Authentication agent forwarding is no longer permitted for virtual accounts sharing a group logon session, or using the SSH Server, Local Service, or Network Service security contexts. Additional protection checks apply to PuTTY agent forwarding.
- Restored recovery from certain Windows S4U logon failures.
- When valid virtual-account credentials are accepted but Windows cannot create the configured security context, the failure no longer incurs a credential penalty or its associated login delay. It still counts toward the total failed-attempt threshold.
Delegated administration:
- Fixed a security issue where delegated administrators could receive private host-key or certificate information without permission to manage host keys and certificates.
- Tightened enforcement of delegated administrators' mount point path restrictions.
Port forwarding:
- Windows accounts can now inherit forwarding from multiple Windows groups. This is controlled by Inherit forwarding from other groups. When enabled, permissions from matching groups are additive, while account-level restrictions take precedence. The default remains inheritance from the primary group only.
- Added Max client-side S2C listeners per user, a server-wide default setting with group and account overrides. The limit applies across all connections for the user. Newly created settings default to 100. For compatibility, upgraded settings use 9,999. Administrators of upgraded instances are encouraged to review and adjust this setting, in particular if settings permit S2C forwarding.
  
  This setting does not affect server-configured S2C port forwarding rules.
- Fixed issues in enforcement of forwarding restrictions. Disabling S2C forwarding permission now also removes existing listeners covered by that permission.
- Fixed forwarding listeners that could remain stalled after a temporary overload. Improved management of Windows Firewall exceptions for forwarding listeners.
File transfer:
- Fixed security issues in enforcement of mount point permissions, filename restrictions, and protection of existing files. Corrected cases where cleanup could affect an unintended file.
- Reworked permissions for newly uploaded files. New-file access is tied more closely to files created in the current file transfer session. Once associated handles are closed and operations complete, access can expire after 15 seconds without successful activity, or sooner when the session's tracking limit is reached. It does not permit resuming an upload after disconnecting.
  
  For Specific directory and Unlimited access mount points, the setting remains Permit Read/Write/Delete New. For other mount point types, it is now named Permit Read/Write/Move New to reflect the supported operations.
- Improved coordination of Move uploads and On-upload commands with open file handles and pending file operations.
  
  When NTFS alternate data streams are enabled, activity on a file and its streams is now grouped for upload processing. This avoids separate upload actions for each stream while retaining separate transfer log entries.
- Fixed issues in buffered and asynchronous file operations that could cause corrupted or incomplete uploads, incorrect success reporting, or stalled cleanup. Errors during final writing or closing are now handled more consistently.
  
  For moves implemented by copying and then deleting, a failure to finish writing the destination no longer permits deletion of the source.
- When filtering directory contents, a directory listing could end before all permitted entries were shown. Fixed.
- Fixed text-mode file positioning which could access the wrong position when counting line separators.
- Improved deletion and error cleanup for encrypted volumes. Changing a volume's size limit no longer disrupts its open files and pending operations.
- For mount points of type Another SFTP server, improved handling of stale file handles after reconnecting and corrected available-space reporting.
- Improved support for updating authorized_keys by renaming the existing file and uploading or renaming a replacement. The server no longer prematurely recreates the file during this workflow. Incomplete replacements are not applied if the file transfer session ends.
FTPS:
- Fixed security issues in TLS handshake processing. Also fixed valid handshakes that could fail depending on how the handshake data arrived, and improved cleanup of passive data connections and server-initiated disconnects.
- Newly generated ECDSA certificate signing requests now use SHA-256 instead of SHA-1. Self-signed ECDSA certificates already used SHA-256.
BvShell and SCP:
- BvShell must now be launched directly by the SSH Server. Starting it through Command Prompt, PowerShell, or another wrapper no longer provides access to the server's virtual filesystem.
  
  Support for external DLL-based filesystem providers and the public SfsDll interface has been removed.
- Use BvShell with WinSCP is now disabled by default in newly created settings. Existing settings are preserved during upgrade. WinSCP has supported SFTP for a long time, so we expect this is no longer commonly needed.
- Tightened restrictions on client-supplied environment variables for restricted shell access types. For Git access only, the only permitted client variable is GIT_PROTOCOL, and permission to accept environment variables must still be enabled.
- Fixed BvShell pipelines that could run despite a startup failure, or hang after another command in the pipeline exited.
- SCP now supports subsecond file timestamps. Corrected timestamp and exit-code reporting, and improved handling of deeply nested directories.
Logging and automation:
- Fixed log entries containing duplicate XML attributes. This could prevent external XML tools from reading the SSH Server's textual log files.
- Improved disconnect summaries and diagnostics for high CPU or memory use.
- Added I_SERVICE_IP_BLOCKED to report the reason and duration of an IP address block.
- When a text-log failure triggers Allow connections from administrators only, existing non-administrator connections are now disconnected as intended.
- PubKeyMaint.ps1 now recognizes public-key use as part of multi-factor authentication. Previously, this use could be missed when identifying unused keys.
- Fixed application of configured TLS requirements when sending email directly to destination mail servers. Also fixed failures to queue messages and incorrect delivery timeout calculations.
- Corrected scriptable settings compatibility properties that could return outdated values or ignore assignments. Fixed creation of path-list entries through scripting.
General:
- Fixed a regression introduced in 9.63 which could cause an internal error during SSH channel cleanup. Improved handling of channels that are starting or closing when a connection ends.
- Improved disconnect and service shutdown when Windows does not finish terminating a subsystem. The SSH Server no longer waits indefinitely for that termination.
- The installation now includes GenCountries.exe, which can generate an updated Countries.bin using either IPLocate.io or MaxMind data. The included country database now uses IPLocate.io data.

Changes in Bitvise SSH Server 9.66: [ 20 July 2026 ]

Release notes:
- We are anticipating an "information security armageddon" due to increasing ability of AI to find security issues, in all software and systems, which were not found in human testing and code review.
  
  The quality of commercially available AI tools has improved to where they are now indispensable for software correctness. We are applying AI tools proactively to find and fix flaws which previously missed detection.
  
  Users will observe this as an increased frequency of significant and important updates. We believe the time to do this is now, before exploitation becomes too easy.
Control Panel and Settings:
- Advanced settings and its windows now open much faster.
  
  Recent Windows versions have become painfully slow to open settings, compared to older Windows versions. We implemented optimizations to restore and improve performance.
- Improved interactive diagnostics for connections that fail due to SSH algorithm mismatches.
SSH:
- Improved multiple avenues which an authenticated client could use to exert disproportionate memory pressure on the server.
- The SSH Server now accepts the client's SSH_MSG_EXT_INFO if the client sends it incorrectly as the next packet after SSH_MSG_SERVICE_REQUEST. Correct client implementations must send this packet after SSH_MSG_NEWKEYS. If the packet is sent late, not all extensions are supported.
  
  If the SSH_MSG_EXT_INFO packet is received even later, this still causes an SSH protocol disconnect.

Changes in Bitvise SSH Server 9.65: [ 11 July 2026 ]

Release notes:
- We are anticipating an "information security armageddon" due to increasing ability of AI to find security issues, in all software and systems, which were not found in human testing and code review.
  
  The quality of commercially available AI tools has improved to where they are now indispensable for software correctness. We are applying AI tools proactively to find and fix flaws which previously missed detection.
  
  Users will observe this as an increased frequency of significant and important updates. We believe the time to do this is now, before it becomes too easy to exploit issues by pointing an AI to an executable binary.
Installation and updates:
- If the SSH Server cannot load instance type settings when upgrading or reinstalling, it now disables checking for updates in new default settings, so that automatic updates remain disabled in case they were disabled previously.
- Reworked corner-case behaviors and status reporting when upgrading settings from much older versions.
Control Panel and Settings:
- Improved reporting for connections stuck in disconnect cleanup.
- If the SSH Server Control Panel cannot load instance type settings, it now more clearly indicates that update settings will also reset to defaults.
Scriptable settings:
- Since version 9.51, the BssCfg command-line configuration utility failed to implement round-trip support for BssCfg settings exportText followed by BssCfg settings importText. Fixed.
Connect profiles:
- When making an outgoing connection via an HTTP CONNECT proxy, the SSH Server now limits the maximum size of received HTTP headers.
General:
- It is possible for SSH Server subsystems to hang indefinitely after a client disconnects. To some extent, this is unavoidable: Windows API functions can hang indefinitely when accessing a network share. If this happens in a file transfer session, the SSH Server's file transfer subsystem hangs until Windows calls return. It is possible that they never return.
  
  In versions before 9.5x, the SSH Server would mitigate this by unconditionally terminating subsystems after a client disconnects. This could cause pending log events and On-upload commands to not be processed.
  
  In recent versions, we removed the unconditional termination, favoring to wait until the subsystem exits. This revealed that some users are seeing indefinite hangs. Connection cleanup can wait indefinitely for stuck subsystems to complete. This can block new connections until the SSH Server is restarted.
  
  The SSH Server now once again terminates stuck subsystems when a client disconnects, as long as the subsystem is not generating further log events or upload notifications. If a subsystem has to be terminated, the SSH Server now performs a diagnostic mini-dump. Recent dumps are retained in the ChildProcessDumps subdirectory of the SSH Server installation directory.
  
  We are not aware of anything we can do about subsystems which are stuck in Windows APIs that do not return on network share access. However: if you see subsystems stuck in situations without network shares, any dumps would be of interest for us to investigate.
- A number of SSH Server settings support environment variable expansion. The SSH Server previously implemented recursive expansion: an expanded variable could reference another one which would also be expanded. This is atypical for Windows applications and could produce unexpected results. When expanding environment variables, the SSH Server now uses a single expansion pass.
- Improved connection disconnect logging.
- The SSH Server is now less permissive with regard to NUL characters in protocol strings where NULs are not expected.
Authentication:
- When handling many new connections from SSH, SFTP or SCP clients that use the none preliminary authentication method, the SSH Server could lock out IP addresses because of the number of none authentication requests, even though no authentication attempt carrying actual credentials failed. Fixed.
File transfer:
- The setting Delete incomplete uploads was available in previous versions, but was ineffective. Fixed.
- The SSH Server now limits the number of file or directory handles which a client may hold open at any one time.
- The SSH Server now performs more effective throttling of file hashing to limit the amount of CPU and memory that can be used by a single client. This favors to avoid penalizing typical use, such as reasonably-sized blocks and hashing of whole files.
- When an On-upload command is configured, the command line can be configured to expand unsafe, client-controlled paths. This remains not recommended: an on-upload script should retrieve paths from environment variables, not command-line parameters.
  
  The SSH Server now performs stricter validation of unsafe environment variable expansion for On-upload commands. Commands that were previously safe should continue to run. The SSH Server is now stricter in refusing commands that could compromise the system.
- Improved worst-case performance of wildcard patterns in FTPS, SCP, BvShell.
- For mount points of type Another SFTP server, the SSH Server now implements a timeout for the duration of the initial SSH key exchange for the outgoing connection.
- Reduced metadata disclosure in less common configurations of mount point permissions.
- Improved handling of errors that may occur while closing files.
- The SSH Server now further restricts client ability to make changes affecting a mount point root directory. This further tightens the fix in 9.39 which prevented mount point roots from being moved.
SFTP:
- The SSH Server now implements more granular limits for the sizes of decoded SFTP strings.
FTPS:
- A variety of FTPS disconnect conditions were previously logged with excessive severity. These are now logged more appropriately.
Port forwarding:
- In previous versions, it was possible for a user to bypass certain custom-configured port forwarding restrictions. Fixed.
- The SSH Server now implements a limit for the number of concurrent client-configured server-to-client port forwarding rules which a single user can have active. Currently, this limit is fixed at 10,000. A warning is logged if the limit is close to being reached.

Security Clarification: [ 24 June 2026 ]

We are receiving inquiries whether our software is affected by the recent libssh2 security issue.

Bitvise software does not use libssh2 and is not affected by this issue.

Changes in Bitvise SSH Server 9.64: [ 22 May 2026 ]

Installation:
- Version 9.63 inadvertently broke compatibility with Windows XP SP3 and Windows Server 2003. Fixed.
Control Panel and Settings:
- Versions 9.61 - 9.63 would load and use a previous splitter position even if it was too large for the current window. This could result in a settings window where only the navigation pane was visible. Fixed.
- Restoring the SSH Server Control Panel after it's hidden to the system tray should now work better if it was previously displayed on a second monitor that was unplugged.
BvShell:
- BvShell now supports command operators && and ||. command1 && command2 executes command2 only if command1 is successful (completes with a zero exit code). command1 || command2 executes command2 only if command1 cannot be executed, or completes with a non-zero exit code.

Changes in Bitvise SSH Server 9.63: [ 16 May 2026 ]

DoS protection:
- The previous Accept delay mechanism is now removed. The accept delay was triggered based on static parameters, instead of whether the SSH Server was actually handling the load. Once triggered, the accept delay would discard incoming connections indiscriminately, including from clients that were not the cause of the load. The rate of incoming connections was limited, but under some conditions, the total number of connections that have not authenticated could still accumulate.
- The SSH Server now uses a new DoS protection mechanism. The new mechanism uses similar settings as Accept delay, but applies them differently. The administrator configures a maximum number of unauthenticated connections that the SSH Server will accept from a single IP address when the server is not otherwise under load. If a client exceeds this limit, or if the server is generally under load, it may start to discard connections. The SSH Server now prefers to accept connections from IP addresses that are less similar to those that are causing the load. When connections authenticate, further new connections can be immediately accepted.
  
  Administrators should no longer need to disable DoS protection to accommodate clients which initiate hundreds of concurrent connections. Administrators may still need to increase the setting Max pre-auth conns from single IP. Clients from other IP addresses that connect at the same time as another aggressive client are now less likely to have their connection refused.
Login serialization:
- The setting Delayed login expiration is now removed. Login attempts that are delayed due to login serialization now expire either consistently with the Login timeout setting for the connection, or after a maximum time if the login timeout is disabled or very long.
- The SSH Server now detects disconnects for connections that are delayed by login serialization, or which receive a Penalty login attempt delay if the configured delay is long.
- For clients connecting using IPv6, the SSH Server would use the full client IPv6 address for login serialization by IP address. The full IPv6 address is too easy for clients to vary. The SSH Server now serializes such login attempts using the 64-bit IPv6 address prefix.
Stuck connection detection:
- SSH Server versions 9.5x and newer support detection and reporting of stuck connections. The SSH Server now detects stuck connections in additional situations, in particular if connection cleanup is delayed by subsystem exit. This can happen if the file transfer subsystem is stuck in a blocking Windows API while attempting to access a network path.
Control Panel and settings:
- In versions 9.61 and 9.62, the Manage password cache interface did not display correctly when using dark mode. Fixed.
- Time-based one-time password (TOTP) authentication: When generating a 2D code for authenticators to scan, commonly used authenticators get confused if the Issuer or Issued to fields contain a colon (":"), even if it's URL-encoded. Colons in these fields are now encoded as the Unicode character U+02D0 (Modifier Letter Triangular Colon).
Scriptable settings:
- In previous SSH Server versions, settings that are retained for scriptable compatibility could be mutated via text import, but not by PowerShell scripts or applications using the BssCfg scriptable COM object. Fixed.
  
  For example: the setting $cfg.settings.connections.penaltyLoginAttemptDelay (seconds) is a scriptable compatibility shim for the newer setting penaltyLoginAttemptDelayMs (milliseconds). A script that sets penaltyLoginAttemptDelay = 3 will now have the effect of setting penaltyLoginAttemptDelayMs = 3000, instead of failing.
Statistics:
- The SSH Server previously created statistics XML files with hashes, but only validated the hashes in some situations. The SSH Server now always validates statistics XML hashes. New hashes are now also calculated more strictly.
FTPS:
- When a client resumes an upload for an existing file, the file would be incorrectly truncated. Fixed.
- FTPS file transfers that end with an error, including a network error, would be incorrectly reported and logged as successful. Fixed.
- FTPS file transfers would previously ignore errors when completing a transfer, such as when closing an uploaded file or flushing a final write before close. Fixed.
- Detection and logging of TLS alerts with fatal severity was previously mishandled. Fixed.
- Double quotes are now escaped if they appear in quoted paths sent in FTPS control connection replies.
- CR and LF characters are now removed if they appear in file or directory names sent in directory listings.
- Control connection commands containing NUL bytes are no longer accepted.
File transfer:
- Fixed an issue which could cause incorrect file access range reporting.
- Mount points of type Another SFTP server: Improved handling for uploads opened for append.
- Mount points of type Another SFTP server: When uploading a file with text conversion, any error during a final write would not be reported or logged. Fixed.
BvShell:
- BvShell now implements a uname command with minimal output. This can help clients which condition further actions based on the uname response.

Changes in Bitvise SSH Server 9.62: [ 4 May 2026 ]

Authentication:
- If one of the IP blocking settings Penalty threshold or Total threshold was disabled (set to 0); but not both; the SSH Server would apply an immediate block on the first failed login attempt. Fixed.
FTPS:
- Fixed a security issue where an FTPS data connection could be matched to the wrong authenticated control connection in some circumstances.
- In Advanced SSH Server settings > TLS algorithms, users can configure restrictions on TLS algorithms for FTPS, in addition to restrictions configured in Windows. In previous SSH Server versions, when used on recent Windows (Windows 10 v1809, Windows Server 2019, or newer), the settings RSA and DH had the opposite effect as intended. Enabling the settings would disable RSA or DH, and disabling the settings would enable them, if they were also enabled in Windows.
  
  The setting for ECDHE operated correctly and is unaffected. SSH, SFTP and SCP are unaffected. Users who disabled RSA and DH key exchange using Windows Schannel settings are unaffected.
- In some circumstances, valid FTPS data connections could be incorrectly rejected with a TLS resume error. Fixed.
- The SSH Server could send an incorrect numeric reply code for some FTPS errors. Clients could interpret the reply code to mean success. Fixed.
SFTP:
- The SSH Server's file transfer subsystem now throttles incoming data more thoroughly while processing expensive requests.

Changes in Bitvise SSH Server 9.61: [ 2 May 2026 ]

General:
- The SSH Server is now more defensive against processing patterns which could cause the SSH Server or its subsystems to allocate large amounts of memory.
FTPS:
- Fixed issue which can allow hijack of FTPS data connections by an attacker on the network path. Users who enable FTPS should update.
Authentication:
- If Windows stalls during Windows account lookup, this would previously stall all connections that require Windows account lookup. The SSH Server cannot fully mitigate blockage due to stalling Windows APIs, but the impact of a single stalled lookup is now less system-wide, and lookup for independent accounts can proceed concurrently.
Auto-execute commands:
- Version 9.51 introduced configurable limits for concurrent execution of custom commands, including On-upload command, Connection on-logon command, On-disconnect command, Windows on-logon command, and Windows on-logoff command. In previous 9.5x versions, these limits were applied incorrectly to also count against commands not yet started, which were still in queue to execute. It was possible for the limits to be exceeded solely by the queued commands. This would cause execution of custom commands to completely stall. Connections that had already disconnected would remain stuck, waiting for command execution and cleanup.
  
  Auto-execute command limits are configured in Advanced settings > Server > Auto-execute commands. Default limits could most readily cause deadlock on servers with a low amount of RAM. If you are using a 9.5x version with custom commands, we recommend updating, while keeping configured limits. If you continue to use a previous 9.5x version, maximally relax the limits under Auto-execute commands.
- Improvements to child process management and monitoring.
Control Panel and Settings:
- When the SSH Server is stopped, the SSH Server Control Panel would previously immediately clear any displayed notifications about warnings and errors. Existing notifications of this type now continue to be displayed until the SSH Server is next started.
- Ctrl+Backspace is now more consistently supported across input elements.
- The Comment field for account settings entries is now also available in Easy settings.
- UI improvements, including for issues related to dark mode.
- Tightened information that is sent to delegated administrator clients without full administrative access.
Scriptable settings:
- A new utility PowerShell script, PubKeyMaint.ps1, is available in the SSH Server installation directory. An administrator can run it, or configure it as a scheduled task, to scan the SSH Server's log files and remove client authentication public keys in SSH Server settings which have not been used for a specified number of days.
Logging:
- The SSH Server now logs elapsed times for all SSH channels, including port forwarding channels.
- Filenames for archived log files now include a dash between the SSH Server instance name and timestamp, consistent with the same change for log files in 9.51.
SSH:
- Cisco clients advertise support for the SSH protocol extension SSH_MSG_EXT_INFO, but incorrectly disconnect if extension information contains binary data. The delay-compression extension sent by the SSH Server contains binary data. The SSH Server will now avoid sending this extension for Cisco clients.
- Tightened environment variable handling for clients which are permitted to set environment variables for terminal shell and exec requests. Permission to set environment variables is disabled by default for virtual accounts, but enabled for Windows accounts.
Port forwarding:
- When accepting port-forwarded connections using server-to-client port forwarding (reverse tunneling), the SSH Server would previously impose a fixed limit of 1 connection per listening socket per 200 ms. This would adversely affect normal use, but could still overburden the server if accept rules were taking a long time to process.
  
  The SSH Server now imposes no accept delay under normal load, and implements throttling if verification for accepted connections is not keeping up with the number of connections that arrive.
File transfer:
- When opening or creating a file on a mount point of type Another SFTP server, the SSH Server now strips access flags not supported by the other SFTP server. In previous versions, such access flags could cause file transfer actions to fail.
- The SSH Server would incorrectly manipulate an SFTP SACL if sent by client. This could cause an incorrect DACL or SACL being set. Fixed.
- The SSH Server could incorrectly continue an SCP transfer for some errors received from the SCP client. Fixed.
- The SSH Server did not correctly throttle some potentially expensive file transfer operations. Fixed.

Changes in Bitvise SSH Server 9.59: [ 18 February 2026 ]

Installation and startup:
- The SSH Server installer still requires administrative rights for installation, but can now be run without administrative rights for help with command-line parameters.
- In previous 8.xx and 9.xx versions, the SSH Server used low-level techniques to improve memory allocation performance on servers that handle many concurrent connections. The improvement is significant, and has worked well for 7+ years. However, after recent Windows updates and hotfixes, some users reported the SSH Server would no longer start, and attempts to reinstall would fail with STATUS_DLL_INIT_FAILED (0xC0000142).
  
  The low-level techniques are inherently sensitive to changes in Windows. We are now seeing these as a surprise with Windows updates and hotfixes. To avoid issues, the SSH Server now disables this low-level functionality by default, but still uses other measures to improve memory allocation performance.
  
  Most users will not notice a performance difference. Servers that handle hundreds of concurrent connections may notice a longer service shutdown. In most cases, this is preferable to the SSH Server not starting after a Windows update.
  
  Most users are not affected by this issue. Users who wish to maximize memory allocation performance can re-enable this by creating two plain text files in the SSH Server installation directory. Name the files BvAlloc32.cfg and BvAlloc64.cfg. In each file, enter a single line:
  
  Hook=yes
  
  This restores the default behavior of previous versions.
- The SSH Server installation now includes a small process startup debugger. The installer will use it automatically for diagnostics in case of STATUS_DLL_INIT_FAILED, which has other possible causes.
Logging:
- In all previous versions, the SSH Server would fail to log events to the Windows Event Log if the size of the event exceeded the ReportEventW per-string limit (31,839 characters). The SSH Server now truncates overly long events. This in particular affects the I_SERVICE_CONFIG_DESCRIPTION event, which can be very large.
  
  In versions before 9.51, Windows Event Log failures were silently ignored. In 9.5x versions, such failures are logged in the SSH Server's textual log files, and displayed in the SSH Server Control Panel.
- The SSH Server now logs an additional I_SERVICE_STOPPING event when initiating service shutdown.
File transfer:
- For virtual filesystem mount points of type Another SFTP server, version 9.32 introduced handling to strip or reduce file open block flags sent by the client if the block flags include SSH_FXF_BLOCK_ADVISORY, if the other SFTP server does not support them. This introduced an issue where the SFTP channel would close abruptly if the other SFTP server does not send the supported2 extension. This is now fixed. Most notably, this would happen if the other server is OpenSSH.
  
  Independently of SSH Server version, it is possible to avoid this issue by configuring the SSH Server to always strip block flags for the affected mount point. This can be done using mount point settings:
  
  File sharing behavior: Force File sharing for uploads: Read, Write, Delete File sharing for downloads: Read, Write, Delete

Changes in Bitvise SSH Server 9.58: [ 6 February 2026 ]

Startup:
- During SSH Server startup, it is unusual, but possible, for Windows APIs to block initialization of SSH Server components for long periods of time. If the delay was very long, the Long Operations Monitor, a new component in versions 9.5x, could exit unexpectedly if other components have not yet initialized.
  
  The initialization sequence is now reorganized to avoid this type of issue. Additionally, long delays during component initialization are now logged at Info or Trace level, depending on the duration.
FTPS:
- For FTPS connections, the SSH Server no longer adds the authorized_keys mount point (by default, "/.ssh") if SSH public key management using authorized_keys is enabled for the user.
  
  Previous 9.5x versions would add this mount point for FTPS, even though SSH public key management is not supported using FTPS. Connections that tried to access this path via FTPS would become unresponsive, although the connection would still respond to disconnect.

Changes in Bitvise SSH Server 9.57: [ 1 February 2026 ]

Updates:
- In some environments, downloading a new version installer fails with Windows error code 12057 (ERROR_INTERNET_SEC_CERT_REV_FAILED). The Windows error description for this error code is misleading. The update interface now provides an error description which is hopefully more useful.
Master/follower synchronization:
- The settings interface now checks that a synchronization password is configured, and that at least one host key or fingerprint for the master server is configured in follower settings. Synchronization cannot work without these settings.
Control Panel:
- In previous versions 9.5x, it was possible for the SSH Server Control Panel to start fully open, instead of creating an icon in the system notification area, if it started before Windows initialized the system notification area. The SSH Server Control Panel now allows extra time for Windows to initialize the system tray. If the tray icon still cannot be created, the Control Panel opens with its window minimized.
Scriptable settings:
- In previous versions, attempting to use the Bitvise.BssCfg COM object from a process without administrative privileges would result in a 30-second delay, followed by an unhelpful error. This now fails promptly with Access is denied.
File transfer:
- We have seen that it's possible for Windows API functions to block indefinitely when attempting to connect to a Windows file share (network share), or when accessing a share, or disconnecting from a share.
  
  The SSH Server now implements more granular logging for connection threads which are stuck disconnecting network shares.
  
  When the SSH Server is shutting down, it now aborts prolonged network share disconnects, but Windows APIs may still block threads indefinitely.
  
  We added a Best practices section in our page Accessing network shares, to help administrators increase reliability of Windows file share connections.

Changes in Bitvise SSH Server 9.56: [ 10 January 2026 ]

Control Panel and Settings:
- Dark mode: If the Windows color mode is set to Light or Custom; and the Windows app mode is set to Light; then list view headers, scrollbars and system menus would appear with light backgrounds instead of dark. Fixed.
Logging:
- It is possible to configure the SSH Server with a very long Penalty login attempt delay, for example if the purpose is to confuse clients that attempt to guess passwords. This would cause previous 9.5x versions to log warnings about stuck connections. This is now logged at Info-level only.

Changes in Bitvise SSH Server 9.53: [ 18 December 2025 ]

Control Panel:
- Tab and pane titles are now more colorful in dark mode, similar to light mode.
Settings:
- Versions 9.51 and 9.52 would incorrectly upgrade configured email notifications to the new Summary notification type, instead of the previous Single notification type. The converted Summary notifications would be configured without a time trigger, so they would be sent only rarely, when something causes them to flush.
  
  Installations that newly update from 9.1x to 9.53+ will now have email notifications upgraded to Single, preserving previous behavior. Installations that previously updated to 9.51 or 9.52, and now have non-working Summary notifications, will assign a default time trigger (1 minute) for Summary notifications that lack time triggers.
- When upgrading to previous 9.xx versions, from significantly older versions, Shell access type settings Git access only and Telnet server would be upgraded incorrectly to non-functional Custom shell settings. Fixed for future upgrades, as long as they are performed directly to 9.53 or higher.
- Monitor CPU usage is now disabled in new settings by default. It produces frequent warnings when the system is simply used normally, particularly on systems with limited resources.
- In settings that were newly created by previous 9.xx versions, it was not sufficient to enable Permit S2C forwarding in order to use server-to-client port forwarding (reverse tunneling). The default Listening rule configured for group settings entries in Advanced settings was initialized with Allow listening disabled. This needed to be enabled, or overridden in account settings, for server-to-client port forwarding to work. This is now fixed for newly created settings, newly created groups, or if the administrator resets group settings to defaults.
- In Easy settings, the labels for Next and Back buttons were incorrectly reversed. Fixed.
Logging:
- Information logged about the currently employed FTPS certificate is now more detailed.
- When an exec request or SCP request is rejected, the sanitized command which the client attempted to execute is now logged.

Changes in Bitvise SSH Server 9.52: [ 13 December 2025 ]

Terminal and exec requests:
- In version 9.51, the bash shell access type did not work, and had to be configured using Custom shell settings. Fixed.

Changes in Bitvise SSH Server 9.51: [ 12 December 2025 ]

Version information:
- This is a new feature release. Feature releases introduce new behaviors, but try to maintain compatibility for upgrading users.
- New feature releases contain new settings which are not understood by previous versions. Settings created or saved using versions 9.5x cannot be used with previous versions.
- If you are using scripts to manage SSH Server settings, version 9.51 contains minor changes to scripting interfaces. Most scripts that use dynamic languages, such as PowerShell, may continue to work without change. Programs that use static languages and link to the SSH Server's COM interfaces need to be updated to use new interface versions.
Password-less authentication:
- On Windows 10, Windows Server 2016 and newer, the SSH Server no longer installs the BvLsa authentication package. The BvLsa package cannot be loaded on recent versions of Windows where LSA protection is enabled by default, or where this setting was enabled by the administrator.
  
  Password-less logon sessions are now created using Windows S4U (Service for User). This permits compatibility with Windows LSA protection and allows the SSH Server to provide full functionality after installation, without requiring a Windows restart.
  
  Windows S4U does not support the Interactive logon type. Logon sessions created using S4U will use the Network logon type, even if a different logon type is configured in SSH Server settings. The Network logon type has been the default for newly created settings since SSH Server versions 7.xx.
  
  The BvLsa authentication package is still installed on older Windows versions, where S4U might not be available, or might not work for local Windows accounts.
Automatic updates:
- Separate proxy settings can now be configured for automatic updates. This allows checks for updates, and downloads of new version installers, to use a different proxy than the one configured in Windows.
- Improved error reporting when the automatic update feature encounters an error.
SSH:
- Bitvise SSH Server, SSH Client and FlowSsh now support hybrid post-quantum and classical key exchange using the key exchange methods mlkem1024nistp384-sha384 and mlkem768x25519-sha256. These key exchange methods use algorithms outside of Windows cryptography. They are only available when FIPS 140 cryptography mode is not enabled in Windows. The new algorithms require Windows Vista or newer.
- In Advanced settings > Key exchange, the SSH Server can now be configured to Require strict key exchange. Strict key exchange is a recent SSH protocol feature supported since Bitvise software versions 9.32. It mitigates the Terrapin vulnerability in SSH implementations prior to December 2023 (CVE-2023-48795). If the SSH connection does not use strict key exchange, the encryption algorithm chacha20-poly1305 is particularly vulnerable.
- The SSH Server now supports public key management using authorized_keys for all account types. Clients which were previously permitted to manage their public keys using the SSH Public Key Subsystem (SPKS) can now also do so using authorized_keys.
  
  The SSH Server now supports this by providing a virtualized authorized_keys file in the user's virtual filesystem. If clients have file transfer access, they can edit this file using SFTP, SCP, FTPS, or BvShell. The location of the authorized_keys file in the virtual filesystem is configurable, and the feature can be disabled. The authorized_keys file is provided on demand, and is not backed by any file in the Windows filesystem.
  
  The previous version of this feature, Synchronize with authorized_keys, is removed. The previous implementation worked only with Windows accounts, was useful only if the user had access to their Windows profile directory, and could unexpectedly reset or remove configured public keys when a user logged off, if the user or administrator was not aware of an authorized_keys file in the user's profile directory.
- The SSH Server now supports configurable limits for the number of channels which a client may concurrently open. This is similar to the OpenSSH setting MaxSessions. Separate limits can be configured for channels which create child processes, and channels of any type.
  
  In previous versions, the SSH Server did not support such limits. An authenticated user with file transfer access could use a single connection to open a large number of SFTP channels, potentially exhausting server resources. This was not reported to occur, and would be evident in SSH Server log files.
FTPS:
- The Manage certificates interface now supports ECDSA. ECDSA private keys can be generated and ECDSA TLS certificates can be imported and employed for FTPS connections. This requires Windows Vista or newer.
Control Panel:
- The SSH Server Control Panel now supports dark mode. This can be enabled using SSH Server Control Panel > App settings. It can also be enabled using the BssCfg command-line configuration utility: BssCfg colorTheme -dark
- The Activity tab now supports more interactive options, including copy to clipboard and right-click IP blocking.
- Improved menu for the SSH Server Control Panel icon in the system notification area. It is now possible to start and stop the SSH Server using the tray icon menu.
- Improved compatibility with Hyper-V Server 2019, where there is no system notification area. In this environment, the SSH Server Control Panel now avoids hiding when minimized.
- Improved reporting of outcomes when importing settings.
Settings:
- SSH Server settings now support filtering lists, including lists of account and group settings. Press Ctrl+F and type a string to show only matching entries.
- The Easy settings and Advanced settings interfaces now support viewing other entries besides the entry that's currently being edited or added. You can view an existing account or group entry while adding another.
- In Advanced settings > Access control, it is now possible to configure a Default virtual group in Advanced settings, and a Default virtual group in Easy settings. Virtual accounts created in Easy settings can now use the specified virtual group, instead of the first group.
- The Maximum forward time-step and Maximum backward time-step settings for TOTP now have server-wide defaults which are configured in Advanced settings > Access control > Time-based one-time password.
- The Easy settings interface now supports configuring Windows file shares for Windows and virtual accounts. It is no longer necessary to switch to Advanced settings to set up access to Windows file shares.
- The log event selection interface now supports right-click or Ctrl+C to copy event names to clipboard.
- In Advanced settings > Connections, the setting Penalty login attempt delay can now be configured with millisecond resolution. This allows configuring a non-zero delay which is shorter than 1 second. In environments that need to relax this setting, a 100-millisecond delay is much better than zero against brute-force password guessing.
- A server-wide default for virtual account password expiration can now be configured in Advanced settings > Access control > Virtual account password policy.
- A default per-user connection limit is now more easily configurable in Advanced settings and Easy settings. The server-wide setting can still be overridden with account- or group-specific values in Advanced settings.
Scriptable settings:
- All objects in scriptable settings now support the .Help() method. This replaces the previous .help property, making commands such as $cfg.settings more useful.
  
  In previous versions, the SSH Server's scriptable settings implemented the .help property: for example, $cfg.settings.help. This was easy to type, but cluttered PowerShell output. For example, $cfg.settings would also dump the help text, making it less usable.
- The BssCfgManip COM object now records important errors, such as those involving COM registration, in the Application section of the Windows Event Log. Previously, an exit code was returned, but error details were not recorded.
- The BssCfg command-line configuration utility now detects if its output is redirected and does not prompt to display more help.
Tasks and notifications:
- The SSH Server now supports summary notifications. Instead of sending an email each time an event occurs, the SSH Server can be configured to collect events and send a periodic summary.
- The SSH Server now supports configurable header text to be included in email notifications.
- The SSH Server now supports configuring tasks with triggers that repeat every several minutes. Previously, to configure a task that runs every 15 minutes, it was necessary to set up many triggers.
- The SSH Server now supports tasks for outgoing SFTP transfers. The sftpc command-line client, which is part of Bitvise SSH Client, is now included with the SSH Server. Configurable file transfer commands use existing sftpc syntax.
Logging:
- It is now possible to configure log filtering where Info or Trace events can be excluded from logging based on scriptable criteria. For example, it is possible to configure a filter where events related to a specific account that generates many connections can be excluded. Log filtering can be configured in Advanced settings > Logging. The scripting syntax is the same as that already used for task triggers.
- The SSH Server now performs periodic, summary logging of blocked connections using the Info-level event I_SERVICE_CONNECTIONS_REJECTED_BLOCKED. This provides more visibility in case any wanted connections are being blocked.
  
  In previous recent versions, the SSH Server did not record any Info-level events for connections blocked due to temporary IP blocking, or due to permanent Client IP address rules. This is necessary to avoid blocked IP addresses from causing unlimited growth of SSH Server log files. However, to troubleshoot wanted but blocked connections, it was necessary to look at the Activity tab in the SSH Server Control Panel, or enable the Trace event T_CONNECT_REJECTED_BLOCKED.
- It is now possible to configure log files to be written without the UTF-8 BOM, for use with tools which do not support the Byte Order Mark.
- Reduced clutter in logged settings dumps from settings which configure lists of log events.
- When logging changes in settings, the generation of textual settings is now more efficient.
- If logging to the Windows Event Log fails, the SSH Server now attempts to log such failures in its textual log files.
- If logging to the Windows Event Log or to textual log files fails, this is now displayed using a banner in the SSH Server Control Panel.
- If textual log file rollover failed, events would be missing from log files without this being apparent in the event sequence number. Sequence numbers are now incremented for the missing events.
- The SSH Server previously logged some events using a log queue, and other events directly. This could cause related events to appear out of order. The SSH Server now logs all events through a log queue. This should improve event ordering. Logging out of order is still possible when related events are logged by different threads.
- Textual log file names now include a dash between the program name and the timestamp.
Statistics:
- Generation of content for statistics files is now more efficient.
Long operation monitoring:
- The SSH Server now monitors individual steps in connections and logon sessions, and periodically reports operations which are taking a long time. Technical information about such delays is now logged in the SSH Server's textual log files, and displayed in the Notes column in the Connections tab in the SSH Server Control Panel. It may take up to 30 seconds for a stuck operation to be detected and reported.
  
  This provides transparency when unexpected delays occur. For example: Windows account lookup is expected to succeed or fail promptly; but in some cases, it has been observed to delay a connection indefinitely. The information provided by this feature allows for troubleshooting.
Authentication:
- Multi-factor authentication (MFA) using a time-based one-time password (TOTP) now supports a configurable grace period. This is enabled in new settings by default, but disabled when upgrading from previous versions to preserve behaviors. A server-wide default can be configured in Advanced settings > Access control > Time-based one-time password.
  
  A TOTP grace period is essential for clients which repeatedly connect and disconnect, and clients which initiate several concurrent connections. With a grace period enabled, the client must pass TOTP for an initial connection, but can make subsequent connections without a TOTP challenge, as long as these connections are from the same IP address, use the same username, and authenticate using another permitted method (for example: password or public key).
- When public key authentication is disabled for a user in Advanced settings, but the user has public keys configured, previous SSH Server versions would respond positively to the client testing which public keys it can use, but then deny authentication using the key. The SSH Server now appropriately denies the public key when queried.
- When logging events related to failed or partially successful authentication, the SSH Server now also logs remaining authentication methods offered to the client.
General:
- When the SSH Server truncates strings, it now avoids creating dangling surrogates and partial newlines.
Windows accounts:
- The SSH Server now supports Group Managed Service Accounts. It is possible to log into gMSA accounts as Windows accounts, or to use them as a virtual account security context.
- The SSH Server now supports public key authentication for Windows accounts using public keys configured in the altSecurityIdentities attribute in Active Directory. If enabled, the SSH Server will check this attribute for any public keys (for example, in OpenSSH format) and will accept them for the user to authenticate.
  
  Public keys configured in Active Directory cannot be altered by the client using SSH Server functionality (the SSH Public Key Subsystem or the authorized_keys interface).
- The SSH Server now supports password-less public key authentication for cross-domain accounts. Windows sessions for such logins are created using Windows S4U (Service for User).
- In domain environments, the SSH Server can encounter long delays attempting to contact the domain controller for the account that's logging in. The SSH Server now supports a configurable timeout for Active Directory queries. By setting this timeout to 0, Active Directory queries can be completely disabled, and the SSH Server can be configured to provide full functionality if Active Directory account information is not available.
  
  This is of particular value for cross-domain logons, where the domain controller for the account domain may be unreachable.
Virtual accounts:
- The SSH Server now supports Windows session sharing between virtual accounts which are members of the same virtual group. This is the default configuration in newly created settings. When upgrading from previous versions, this feature is disabled to preserve behavior. It can be enabled for each virtual account in Advanced settings, in the account settings entry.
  
  Windows session sharing is a feature introduced in versions 9.1x which can dramatically improve duration and reliability of connections to network shares. It is particularly effective for accounts which connect and disconnect frequently. For connections which load a Windows profile, it can reduce issues from frequent Windows profile loading.
  
  The extension of session sharing to virtual groups improves scenarios where there are many connections from different virtual accounts, and each account may connect relatively infrequently. If the accounts are all accessing the same network shares, allowing them to share a Windows logon session further reduces the number of network share connections that must be made. This improves reliability by reducing the number of network share connections.
Auto-execute commands:
- The SSH Server now monitors the memory used by custom commands and throttles their execution. Settings for this can be configured in Advanced settings > Server > Auto-execute commands.
  
  The SSH Server supports custom commands which can be configured to run when a user authenticates or disconnects, when a Windows logon session is created or destroyed, or after a user uploads a file. The On-upload command is asynchronous and can start many concurrent instances if a client disconnects after uploading many small files.
  
  Administrators commonly use PowerShell, which has a large memory footprint. When using a PowerShell script, processing 1,000 On-upload commands for 1,000 small files may require 60 GB of RAM. The Windows Command Prompt is more frugal, and could handle the same load using 3 GB.
- The SSH Server now tracks custom commands to their completion and logs their exit codes.
- The SSH Server now records the output of custom commands and logs it by default. This reduces or eliminates the need for commands to use their own logging to diagnose issues or audit execution.
File transfer:
- Since version 9.34, the SSH Server has opened files which are being uploaded to non-local storage (e.g. uploads to file shares) using unbuffered I/O. This can noticeably improve upload performance, but there are situations where the network share server does not set the file size correctly.
  
  This version adds mount point settings, and a server-wide default setting, to control the use of unbuffered I/O.
- The SSH Server now supports the vendor-id extension which is sent by some SFTP clients. If received, the content is now logged in the event I_SFTP_SERVER_CLIENT_VENDOR_ID.

Known issues

curl version 8.21 breaks FTPS TLS resume for data connections when using -k or --insecure. Users commonly use this when connecting to an FTPS server with a self-signed TLS certificate.

The issue was fixed for curl 8.22, but the affected curl 8.21 version was deployed widely in July 2026 Windows updates.

Best solution: If you are using a self-signed FTPS certificate, do not use -k or --insecure. Instead, use --cacert <certificate-file>. This is secure, authenticates the FTPS server, and avoids the 8.21 issue. For more details, see Using curl.
FileZilla versions 3.70.0 and .1 fail to validate host key signatures using the host key algorithm ECDSA/nistp384 (ecdsa-sha2-nistp384). This is a common host key type used by Bitvise SSH Server. FileZilla disconnects with message: "Could not verify signature over exchange hash". This is resolved in FileZilla version 3.70.2.