[3.12] gh-149486: tarfile.data_filter: validate written link target (GH-149487)#149556
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…ythonGH-149487) The data filter rewrote linknames with normpath() but ran the containment check against the un-normalised value, and computed a symlink's directory before stripping trailing slashes. Both let a crafted archive create links pointing outside the destination. Also reject link members that resolve to the destination directory itself, which could otherwise replace it with a symlink and redirect all subsequent members. (Patch by Greg; Petr's just reviewing & merging.) (cherry picked from commit 5784119) Co-authored-by: Petr Viktorin <encukou@gmail.com> Co-authored-by: Gregory P. Smith <greg@krypto.org>
This was referenced May 8, 2026
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The data filter rewrote linknames with normpath() but ran the
containment check against the un-normalised value, and computed a
symlink's directory before stripping trailing slashes. Both let a
crafted archive create links pointing outside the destination. Also
reject link members that resolve to the destination directory itself,
which could otherwise replace it with a symlink and redirect all
subsequent members.
(Patch by Greg; Petr's just reviewing & merging.)
(cherry picked from commit 5784119)
Co-authored-by: Petr Viktorin encukou@gmail.com
Co-authored-by: Gregory P. Smith greg@krypto.org