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gh-156026: Add warning about link targets to tarfile.tar_filter #159019

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Merged
ethanfurman merged 2 commits into from
Oct 14, 2026
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gh-156026: Add warning about link targets to tarfile.tar_filter #159019

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gh-156026: Add warning about link targets to tarfile.tar_filter
encukou Oct 8, 2026
1e9aad6
Merge branch 'main' into tarfile-outside-doc
ethanfurman Oct 14, 2026
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18 changes: 7 additions & 11 deletions Doc/library/tarfile.rst
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Expand Up @@ -1137,17 +1137,13 @@ reused in custom filters:
Return the modified ``TarInfo`` member.

.. warning::
This filter does not check :attr:`TarInfo.linkname`. This means it does
not limit where a symbolic link member points. An absolute symbolic-link
target will remain absolute, and a relative target may resolve outside the
extraction destination. The destination path protection described above
concerns only where the archive member itself is written, not where a
symbolic link resolves. The stricter :func:`data_filter` rejects these
unsafe link targets, raising :class:`~tarfile.AbsoluteLinkError` for
absolute link targets or :class:`~tarfile.LinkOutsideDestinationError`
for link targets outside the destination.

.. versionchanged:: 3.16

This filter does not check link targets (:attr:`TarInfo.linkname`).
It allows benign cases (like links to ``/dev/null``), but it also allows
links (symbolic and hard) to arbitrary files on the filesystem,
potentially granting unintended access to these files.

.. versionchanged:: next

Filenames containing ``..`` components are now normalized.

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