CVE-2026-28356

Name	CVE-2026-28356
Description	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.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
References	DSA-6161-1

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
multipart (PTS)	trixie	1.2.1-2	vulnerable
	trixie (security)	1.2.1-2+deb13u1	fixed
	forky, sid	1.3.1-1	fixed

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
multipart	source	trixie	1.2.1-2+deb13u1		DSA-6161-1
multipart	source	(unstable)	1.3.1-1

Notes

https://github.com/defnull/multipart/security/advisories/GHSA-p2m9-wcp5-6qw3
Fixed by: https://github.com/defnull/multipart/commit/7e4fe6faaf64b2088faa5533a1a1c21c3c94c60c (v1.3.1)
Fixed by: https://github.com/defnull/multipart/commit/d6f79b30ee21904ab552950acfe4aae79fa55d3d (v1.2.2)