CVE-2026-6100

Description

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.

References

https://mail.python.org/archives/list/[email protected]/thread/HTWB2Z6KT5QQX4RYEZAFININDHNOSIF3/

https://github.com/python/cpython/pull/148396

https://github.com/python/cpython/issues/148395

https://github.com/python/cpython/commit/e20c6c9667c99ecaab96e1a2b3767082841ffc8b

https://github.com/python/cpython/commit/c3cf71c3366fe49acb776a639405c0eea6169c20

https://github.com/python/cpython/commit/8fc66aef6d7b3ae58f43f5c66f9366cc8cbbfcd2

https://github.com/python/cpython/commit/6a5f79c8d7bbf22b083b240910c7a8781a59437d

https://github.com/python/cpython/commit/47128e64f98c3a20271138a98c2922bea2a3ee0e

http://www.openwall.com/lists/oss-security/2026/04/13/10

Details

Source: Mitre, NVD

Risk Information

CVSS v2

CVSS v3

CVSS v4

EPSS