Expired Pointer Dereference SNYK-RHEL9-PYTHON3LIBS-16072163 #18064

NVD Description

Note: Versions mentioned in the description apply only to the upstream python3-libs package and not the python3-libs package as distributed by RHEL.
See How to fix? for RHEL:9 relevant fixed versions and status.

Use-after-free (UAF) was possible in the lzma.LZMADecompressor, bz2.BZ2Decompressor, and gzip.GzipFile when a memory allocation fails with a MemoryError and the decompression instance is re-used. This scenario can be triggered if the process is under memory pressure. The fix cleans up the dangling pointer in this specific error condition.

The vulnerability is only present if the program re-uses decompressor instances across multiple decompression calls even after a MemoryError is raised during decompression. Using the helper functions to one-shot decompress data such as lzma.decompress(), bz2.decompress(), gzip.decompress(), and zlib.decompress() are not affected as a new decompressor instance is used per call. If the decompressor instance is not re-used after an error condition, this usage is similarly not vulnerable.

Remediation

Upgrade RHEL:9 python3-libs to version 0:3.9.25-3.el9_7.3 or higher.
This issue was patched in RHSA-2026:10949.

References

• https://access.redhat.com/security/cve/CVE-2026-6100
• python/cpython@6a5f79c
• python/cpython@8fc66ae
• python/cpython@c3cf71c
• [CVE-2026-6100] Possible UAF in {LZMA,BZ2,_Zlib}Decompressor python/cpython#148395
• gh-148395: Fix a possible UAF in {LZMA,BZ2,_Zlib}Decompressor python/cpython#148396
• https://mail.python.org/archives/list/security-announce@python.org/thread/HTWB2Z6KT5QQX4RYEZAFININDHNOSIF3/
• http://www.openwall.com/lists/oss-security/2026/04/13/10
• python/cpython@47128e6
• python/cpython@e20c6c9
• python/cpython@ea8d735
• https://access.redhat.com/errata/RHSA-2026:10949
• https://bugzilla.redhat.com/show_bug.cgi?id=2457932
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-6100.json