Apache Module mod_dav

Summary

This module provides class 1 and class 2 WebDAV ('Web-based Distributed Authoring and Versioning') functionality for Apache. This extension to the HTTP protocol allows creating, moving, copying, and deleting resources and collections on a remote web server.

Topics

• Enabling WebDAV
• Security Issues
• Complex Configurations

Directives

• Dav
• DavBasePath
• DavDepthInfinity
• DavMinTimeout

Bugfix checklist

• httpd changelog
• Known issues
• Report a bug

See also

• DavLockDB
• LimitXMLRequestBody
• WebDAV Resources

Enabling WebDAV ¶

To enable mod_dav, add the following to a container in your httpd.conf file:

Dav On

This enables the DAV file system provider, which is implemented by the mod_dav_fs module. Therefore, that module must be compiled into the server or loaded at runtime using the LoadModule directive.

In addition, a location for the DAV lock database must be specified in the global section of your httpd.conf file using the DavLockDB directive:

DavLockDB /usr/local/apache2/var/DavLock

The directory containing the lock database file must be writable by the User and Group under which Apache is running.

In the example below, <RequireAny> is used to ensure that DAV-specific methods (i.e., methods other than GET, POST and OPTIONS) are limited to the authenticated user.

If you want to set the maximum amount of bytes that a DAV client can send at one request, you have to use the LimitXMLRequestBody directive. The "normal" LimitRequestBody directive has no effect on DAV requests.

DavLockDB "/usr/local/apache2/var/DavLock"

<Directory "/usr/local/apache2/htdocs/foo">
    Dav On

    AuthType Basic
    AuthName DAV
    AuthUserFile "user.passwd"

    <RequireAny>
        Require method GET POST OPTIONS
        Require user admin
    </RequireAny>
</Directory>

Security Issues ¶

Since DAV access methods allow remote clients to manipulate files on the server, you must take particular care to assure that your server is secure before enabling mod_dav.

Any location on the server where DAV is enabled should be protected by authentication. The use of HTTP Basic Authentication is not recommended. You should use at least HTTP Digest Authentication, which is provided by the mod_auth_digest module. Nearly all WebDAV clients support this authentication method. An alternative is Basic Authentication over an SSL enabled connection.

In order for mod_dav to manage files, it must be able to write to the directories and files under its control using the User and Group under which Apache is running. New files created will also be owned by this User and Group. For this reason, it is important to control access to this account. The DAV repository is considered private to Apache; modifying files outside of Apache (for example using FTP or filesystem-level tools) should not be allowed.

mod_dav may be subject to various kinds of denial-of-service attacks. The LimitXMLRequestBody directive can be used to limit the amount of memory consumed in parsing large DAV requests. The DavDepthInfinity directive can be used to prevent PROPFIND requests on a very large repository from consuming large amounts of memory. Another possible denial-of-service attack involves a client simply filling up all available disk space with many large files. There is no direct way to prevent this in Apache, so you should avoid giving DAV access to untrusted users.

Complex Configurations ¶

One common request is to use mod_dav to manipulate dynamic files (PHP scripts, CGI scripts, etc). This is difficult because a GET request will always run the script, rather than downloading its contents. One way to avoid this is to map two different URLs to the content, one of which will run the script, and one of which will allow it to be downloaded and manipulated with DAV.

Alias "/phparea" "/home/gstein/php_files"
Alias "/php-source" "/home/gstein/php_files"
<Location "/php-source">
    Dav On
    ForceType text/plain
</Location>

With this setup, http://example.com/phparea can be used to access the output of the PHP scripts, and http://example.com/php-source can be used with a DAV client to manipulate them.

Dav Directive ¶

Use the Dav directive to enable the WebDAV HTTP methods for the given container:

<Location "/foo">
    Dav On
</Location>

The value On is actually an alias for the default provider filesystem which is served by the mod_dav_fs module. Note, that once you have DAV enabled for some location, it cannot be disabled for sublocations. For a complete configuration example have a look at the section above.

DavBasePath Directive ¶

If a DAV repository is configured using a regular expression match (such as LocationMatch) then mod_dav will not be able to find the root of the repository from the pathname alone. Third-party providers (for example, Subversion's mod_dav_svn) may fail to handle requests without the correct repository root.

To allow providers to work correctly in such a configuration, DavBasePath must be used.

<LocationMatch "^/repos/">
    Dav svn
    DavBasePath /repos
    SVNParentPath /var/svn
</LocationMatch>

DavDepthInfinity Directive ¶

Use the DavDepthInfinity directive to allow the processing of PROPFIND requests containing the header 'Depth: Infinity'. Because this type of request could constitute a denial-of-service attack, by default it is not allowed.

DavMinTimeout Directive ¶

When a client requests a DAV resource lock, it can also specify a time when the lock will be automatically removed by the server. This value is only a request, and the server can ignore it or inform the client of an arbitrary value.

Use the DavMinTimeout directive to specify, in seconds, the minimum lock timeout to return to a client. Microsoft Web Folders defaults to a timeout of 120 seconds; the DavMinTimeout can override this to a higher value (like 600 seconds) to reduce the chance of the client losing the lock due to network latency.

<Location "/MSWord">
    DavMinTimeout 600
</Location>