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CVE-2026-6100

Use-after-free in lzma.LZMADecompressor, bz2.BZ2Decompressor, and gzip.GzipFile after re-use under memory pressure PUBLISHED

Description (CNA)

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.

Affected (CNA)

Vendor / productVersions
Python Software Foundation / CPythonaffected 0 before 3.10.21; affected 3.11.0 before 3.11.16; affected 3.12.0 before 3.12.14; affected 3.13.0 before 3.13.14; affected 3.14.0a1 before 3.14.5rc1; affected 3.15.0a1 before 3.15.0b1

CWE

CWE-416, CWE-787

References

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.

CVE

No English description supplied.

redhat-SADP

A flaw was found in Python's decompression modules, including `lzma.LZMADecompressor`, `bz2.BZ2Decompressor`, and `gzip.GzipFile`. This vulnerability, a use-after-free, can occur if a program attempts to re-use a decompression object after a memory allocation error, especially when the system is experiencing high memory usage. Exploitation of this flaw could potentially allow an attacker to execute arbitrary code or access sensitive data. 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.