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GeezerVison is showing github.com — gh-42400: Fix buffer overflow in _Py_wrealpath for long paths by ashm-dev · Pull Request #141529 · python/cpython

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@ashm-dev

@ashm-dev ashm-dev commented Nov 13, 2025 •
edited by bedevere-app Bot
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Fixes buffer overflow (CVE-2006-1542) in _Py_wrealpath() when handling paths longer than MAXPATHLEN (4096 bytes).

Changed realpath(path, buffer) to realpath(path, NULL) for dynamic allocation.

Closes #42400

  • Issue: Avoid using unsafe realpath #42400

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@bedevere-app bedevere-app Bot added the awaiting review label Nov 13, 2025
@bedevere-app bedevere-app Bot mentioned this pull request Nov 13, 2025
Avoid using unsafe realpath #42400
Closed
@ashm-dev
pythongh-42400: Fix buffer overflow in _Py_wrealpath for long paths
3255a3d
@ashm-dev
ashm-dev force-pushed the fix/cve-realpath branch from 1424245 to 3255a3d Compare November 13, 2025 19:41
@ashm-dev
pythongh-42400: Fix buffer overflow in _Py_wrealpath for long paths
bb4af8a
@ashm-dev
ashm-dev force-pushed the fix/cve-realpath branch from 52f60a5 to bb4af8a Compare November 13, 2025 20:36
ashm-dev added 2 commits November 13, 2025 23:45
@ashm-dev
fix
a12ee2d
@ashm-dev
Use os.samefile in realpath symlink test
238ff0e 
Allow platforms where realpath returns different canonical paths (e.g.
Android). Verify resolution with os.samefile and fall back to a length
check if samefile is unavailable.
@ashm-dev

ashm-dev commented Nov 13, 2025

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I don't think the errors in the UBSAN test are related to this fix, as they occur for a completely different reason and generally in import tests.
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@ashm-dev

ashm-dev commented Nov 14, 2025

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@vstinner Could you please review this PR?
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vstinner
vstinner reviewed Nov 14, 2025
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Comment thread Misc/NEWS.d/next/Security/2025-11-13-22-31-56.gh-issue-42400.pqB5Kq.rst Resolved

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Comment thread Lib/test/test_fileutils.py Resolved

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ashm-dev and others added 3 commits November 14, 2025 14:04
@ashm-dev
Merge remote-tracking branch 'upstream/main' into fix/cve-realpath
d8a437a
@ashm-dev
remove tests
88368ec
@ashm-dev @vstinner
Update Misc/NEWS.d/next/Security/2025-11-13-22-31-56.gh-issue-42400.p…
1cf6fde 
…qB5Kq.rst

Co-authored-by: Victor Stinner <[email protected]>
@ashm-dev
ashm-dev requested a review from vstinner November 14, 2025 11:08
@vstinner
Merge branch 'main' into fix/cve-realpath
f882e26
@vstinner

vstinner commented Nov 14, 2025

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I updated the PR to retrieve the fix for the UBSan CI.
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@vstinner vstinner added the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Nov 17, 2025
@bedevere-bot

bedevere-bot commented Nov 17, 2025

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🤖 New build scheduled with the buildbot fleet by @vstinner for commit f882e26 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F141529%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.
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@bedevere-bot bedevere-bot removed the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Nov 17, 2025
@vstinner

vstinner commented Nov 17, 2025

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realpath(path, NULL) seems to be a recent feature. Let me check on buildbots if it's supported by all platforms supported by Python.
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@vstinner
vstinner merged commit daafacf into python:main Nov 18, 2025
112 of 118 checks passed

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@bedevere-app bedevere-app Bot removed the awaiting review label Nov 18, 2025
@vstinner

vstinner commented Nov 18, 2025

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Change merged, thanks.

The change passed on our fleet of stable buildbots.

Even if the change was documented in the Security category, I don't think that it's worth it to backport it to stable branches (yet). I'm afraid of breaking the Python build on some weird platforms where realpath(path, NULL) is not supported. So I prefer to make the change only in the main branch for now.
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@ashm-dev
ashm-dev deleted the fix/cve-realpath branch November 18, 2025 17:35
StanFromIreland pushed a commit to StanFromIreland/cpython that referenced this pull request Dec 6, 2025
@ashm-dev @vstinner @StanFromIreland
pythongh-42400: Fix buffer overflow in _Py_wrealpath() for very long …
05021ff 
…paths (python#141529)

Co-authored-by: Victor Stinner <[email protected]>
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@ashm-dev @vstinner @bedevere-bot
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