---
id: CVE-2026-6100
title: >-
  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
summary: >-
  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…
severity: high
cvss: 8.1
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-416
  - CWE-787
  - CWE-825
published: '2026-04-13'
updated: '2026-08-05'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-6100'
references:
  - url: >-
      https://github.com/python/cpython/commit/47128e64f98c3a20271138a98c2922bea2a3ee0e
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  - url: >-
      https://github.com/python/cpython/commit/6a5f79c8d7bbf22b083b240910c7a8781a59437d
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      https://github.com/python/cpython/commit/8fc66aef6d7b3ae58f43f5c66f9366cc8cbbfcd2
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  - url: >-
      https://github.com/python/cpython/commit/c3cf71c3366fe49acb776a639405c0eea6169c20
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  - url: >-
      https://github.com/python/cpython/commit/e20c6c9667c99ecaab96e1a2b3767082841ffc8b
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  - url: >-
      https://github.com/python/cpython/commit/ea8d735eb084cf8cc021df1a30e90d10a8f052e3
    label: cna@python.org
  - url: 'https://github.com/python/cpython/issues/148395'
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  - url: 'https://github.com/python/cpython/pull/148396'
    label: cna@python.org
  - url: >-
      https://mail.python.org/archives/list/security-announce@python.org/thread/HTWB2Z6KT5QQX4RYEZAFININDHNOSIF3/
    label: cna@python.org
  - url: 'http://www.openwall.com/lists/oss-security/2026/04/13/10'
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tags:
  - nvd
epss: 0.00761
epssPercentile: 0.53328
ingestedAt: '2026-08-05T11:47:24.542Z'
---

## Overview

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

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.