Inefficient Regular Expression Complexity Affecting multipart package, versions <1.3.1-1


Severity

Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.72% (50th percentile)

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  • Snyk IDSNYK-DEBIANUNSTABLE-MULTIPART-15562031
  • published14 Mar 2026
  • disclosed12 Mar 2026

Introduced: 12 Mar 2026

CVE-2026-28356  (opens in a new tab)
CWE-1333  (opens in a new tab)

How to fix?

Upgrade Debian:unstable multipart to version 1.3.1-1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream multipart package and not the multipart package as distributed by Debian. See How to fix? for Debian:unstable relevant fixed versions and status.

multipart is a fast multipart/form-data parser for python. Prior to 1.2.2, 1.3.1 and 1.4.0-dev, the parse_options_header() function in multipart.py uses a regular expression with an ambiguous alternation, which can cause exponential backtracking (ReDoS) when parsing maliciously crafted HTTP or multipart segment headers. This can be abused for denial of service (DoS) attacks against web applications using this library to parse request headers or multipart/form-data streams. The issue is fixed in 1.2.2, 1.3.1 and 1.4.0-dev.

CVSS Base Scores

version 3.1