CVE-2026-54911

Name	CVE-2026-54911
Description	UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.13.0, ujson.dumps() (or ujson.dump() or ujson.encode()) have a reject_bytes=False option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different Unicode characters instead of rejecting them. This leads to input validation bypass and data integrity issues. This vulnerability is fixed in 5.13.0.
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)
Debian Bugs	1140630

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
ujson (PTS)	bullseye	4.0.2-1	vulnerable
	bookworm	5.7.0-1	vulnerable
	trixie	5.10.0-1	vulnerable
	forky, sid	5.13.0-1	fixed

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

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
ujson	source	(unstable)	5.13.0-1			1140630

Notes

[trixie] - ujson <no-dsa> (Minor issue)
[bookworm] - ujson <postponed> (Minor issue)
[bullseye] - ujson <postponed> (Minor issue)
https://github.com/ultrajson/ultrajson/security/advisories/GHSA-3j69-69wj-xqx2
https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf (5.13.0)