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gh-149449: Fix use-after-free in _PyUnicode_GetNameCAPI#150323

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eendebakpt:fix-ucnhash-capi-uaf
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gh-149449: Fix use-after-free in _PyUnicode_GetNameCAPI#150323
eendebakpt wants to merge 1 commit into
python:mainfrom
eendebakpt:fix-ucnhash-capi-uaf

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@eendebakpt eendebakpt commented May 23, 2026

The cache stored the raw struct pointer extracted from unicodedata's _ucnhash_CAPI capsule without keeping a reference to the owning capsule. Dropping the module from sys.modules and running gc.collect() then freed the struct while \N{...} decoding and the namereplace codec handler were still using it. Hold a strong reference to the capsule on the interpreter state and Py_CLEAR it in _PyUnicode_Fini.

This needs backports I think, as it also affects python versions 3.10 to 3.15.

Claude was used to construct a PR.

The cache stored the raw struct pointer extracted from
unicodedata's _ucnhash_CAPI capsule without keeping a
reference to the owning capsule. Dropping the module from
sys.modules and running gc.collect() then freed the struct
while \N{...} decoding and the namereplace codec handler
were still using it. Hold a strong reference to the
capsule on the interpreter state and Py_CLEAR it in
_PyUnicode_Fini.
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