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.

How to fix CVE-2026-6100

To remediate CVE-2026-6100, upgrade the affected package to a fixed version below.

• —upgrade to 3.14.5 or later
• —upgrade to 3.14.5 or later
• —upgrade to 3.14.5 or later
• —no fix listed
• —no fix listed
• —upgrade to 3.13.5-2+deb13u2 or later
• —upgrade to 3.14.5~rc1-1 or later
• —upgrade to 3.9.2-1+deb11u6 or later

Is CVE-2026-6100 being exploited?

Low — EPSS is 0.2%, meaning exploitation activity has not been observed at scale.

Affected packages (8)

• from 0, < 3.14.5
• from 0, < 3.14.5
• from 0, < 3.14.5
• from 0
• from 0
• from 0, < 3.13.5-2+deb13u2
• from 0, < 3.14.5~rc1-1
• from 0, < 3.9.2-1+deb11u6

CVSS scores

References (11)

• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-6100
• WEBgithub.com/python/cpython/commit/47128e64f98c3a20271138a98c2922bea2a3ee0e
• WEBgithub.com/python/cpython/commit/6a5f79c8d7bbf22b083b240910c7a8781a59437d
• WEBgithub.com/python/cpython/commit/8fc66aef6d7b3ae58f43f5c66f9366cc8cbbfcd2