CVE-2026-6100: Use-after-free in lzma.LZMADecompressor, bz2.BZ2Decompressor, and gzip.GzipFile after re-use under memory pressure

Versions reported by the vendor

Affected version ranges reported by the assigning authority (PSF). Independent of NVD's CPE analysis and usually ahead of it.

• Python Software Foundation CPython

  • before 3.10.21affected · python
  • 3.11.0 and later · before 3.11.16affected · python
  • 3.12.0 and later · before 3.12.14affected · python
  • 3.13.0 and later · before 3.13.14affected · python
  • 3.14.0a1 and later · before 3.14.5rc1affected · python
  • 3.15.0a1 and later · before 3.15.0b1affected · python

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Other highest-scoring records for the same primary product.

• CVE-2026-115557Distrust compromised intermediate certificates in ssl module
  37Monitor
• CVE-2025-4517Arbitrary writes via tarfile realpath overflow
  37Monitor
• CVE-2026-19445Use-after-free of a server-side SSLContext when sni_callback switches contexts
  36Monitor

Published before and after this one in the same product

• ← EarlierCVE-2026-1502Apr 10, 2026 · HTTP client proxy tunnel headers not validated for CR/LF
  22Monitor
• ← EarlierCVE-2026-3446Apr 10, 2026 · Base64 decoding stops at first padded quad by default
  24Monitor
• Later →CVE-2026-4786Apr 13, 2026 · Incomplete mitigation of CVE-2026-4519, %action expansion for command injection to webbrowser.open()
  28Monitor

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

1free(dev->buf);2/* ... another thread is still running ... */3process(dev->buf);

1lock(&dev->lock);2free(dev->buf);3dev->buf = NULL;4unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.