FreeBSD : Python -- use-after-free vulnerability in decompressors under memory pressure (b8e9f33c-375d-11f1-a119-e36228bfe7d4)

critical Nessus Plugin ID 307387

Synopsis

The remote FreeBSD host is missing one or more security-related updates.

Description

The version of FreeBSD installed on the remote host is prior to tested version. It is, therefore, affected by a vulnerability as referenced in the b8e9f33c-375d-11f1-a119-e36228bfe7d4 advisory.

Seth Larson reports:
There is a CRITICAL severity vulnerability affecting CPython.
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 created for each call. If the decompressor instance is not re-used after an error condition, this usage is similarly not vulnerable.

Tenable has extracted the preceding description block directly from the FreeBSD security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Solution

Update the affected packages.

Plugin Details

Severity: Critical

ID: 307387

File Name: freebsd_pkg_b8e9f33c375d11f1a119e36228bfe7d4.nasl

Version: 1.1

Type: Local

Family: FreeBSD Local Security Checks

Published: 4/17/2026

Updated: 4/17/2026

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 6.0

CVSS v2

Risk Factor: High

Base Score: 7.5

Temporal Score: 5.5

Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:P

CVSS Score Source: CVE-2026-6100

CVSS v3

Risk Factor: Critical

Base Score: 9.8

Temporal Score: 8.5

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

CVSS v4

Risk Factor: Critical

Base Score: 9.1

Threat Score: 6.9

Threat Vector: CVSS:4.0/E:U

Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Vulnerability Information

CPE: p-cpe:/a:freebsd:freebsd:python312, p-cpe:/a:freebsd:freebsd:python310, p-cpe:/a:freebsd:freebsd:python313, cpe:/o:freebsd:freebsd, p-cpe:/a:freebsd:freebsd:python311, p-cpe:/a:freebsd:freebsd:python314

Required KB Items: Host/local_checks_enabled, Host/FreeBSD/release, Host/FreeBSD/pkg_info

Exploit Ease: No known exploits are available

Patch Publication Date: 4/13/2026

Vulnerability Publication Date: 2/12/2026

Reference Information

CVE: CVE-2026-6100

IAVA: 2026-A-0142-S

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