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GeezerVison is showing github.com — gh-112887: Fix tarfile FilterError handling to skip member extraction by mattprodani · Pull Request #112954 · python/cpython

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@mattprodani

@mattprodani mattprodani commented Dec 11, 2023 •
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In tarfile library, if a FilterError is raised for a member during TarFile.extract() or TarFile.extractall() with errorlevel set to 0, a debugging message is correctly logged but the unsafe member is still extracted. Based on the documentation and a look at the code, it seems that the desired expectation with errorlevel=0 is to not raise an exception, but skip member extraction and log the error.
Updates tarfile to properly handle FilterError and skip extraction on unsafe members even when an exception is not raised.

This issue was reported on Python 3.11 and should likely be backported as it is a security issue.

From the docs:

When a filter refuses to extract a file, it will raise an appropriate exception, a subclass of FilterError. This will abort the extraction if TarFile.errorlevel is 1 or more. With errorlevel=0 the error will be logged and the member will be skipped, but extraction will continue.

  • Issue: [CVE-2025-4435] tarfile still extracts problematic files when filter is set and errorlevel is 0 #112887

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mattprodani added 2 commits December 1, 2023 15:13
@mattprodani
Fix tarfile FilterError handling to skip member extraction
c981c3d 
In `tarfile` library, FilterError with error_level set to 0 correctly logged a debugging
message but did not properly skip extraction of a member. Updates filter
functions to return None when a FilterError is seen, as stated in docs.
@mattprodani
add and fix tests for filtererror
191998a
@bedevere-app bedevere-app Bot mentioned this pull request Dec 11, 2023
[CVE-2025-4435] tarfile still extracts problematic files when filter is set and errorlevel is 0 #112887
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@mattprodani mattprodani changed the title gh-112887: Fix tarfile FilterError handling to skip member extraction gh-112887: [WIP] Fix tarfile FilterError handling to skip member extraction Dec 11, 2023
@mattprodani
mattprodani force-pushed the safetar branch from 3243699 to c981c3d Compare December 11, 2023 21:53
@mattprodani mattprodani changed the title gh-112887: [WIP] Fix tarfile FilterError handling to skip member extraction gh-112887: Fix tarfile FilterError handling to skip member extraction Dec 12, 2023
@blurb-it
📜🤖 Added by blurb_it.
9812823
@mattprodani
mattprodani marked this pull request as ready for review December 12, 2023 20:37
@mattprodani
mattprodani requested a review from ethanfurman as a code owner December 12, 2023 20:37
@bedevere-app bedevere-app Bot added the awaiting review label Dec 12, 2023
@encukou

encukou commented Jun 4, 2025

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Thank you for the fix. I included it, in a “Ship of Theseus” style, in #135037 which fixes a few other security issues as well.

I forgot to include you in the Git authorship metadata. I apologize for that. You're credited in What's New though: https://docs.python.org/3.14/whatsnew/3.14.html#tarfile
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@encukou encukou closed this Jun 4, 2025
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@ethanfurman ethanfurman Awaiting requested review from ethanfurman ethanfurman is a code owner

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@mattprodani @encukou
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