CVE-2026-93990

Name	CVE-2026-93990
Description	Expat before 2.8.5 fails to validate that a high surrogate in UTF-16 input is followed by a low surrogate, allowing malformed UTF-16 sequences to be accepted. Attackers can supply UTF-16 encoded XML containing lone high surrogates that consume the following code unit, causing Expat to pass unpaired surrogates to applications built with XML_UNICODE and to silently replace input characters in other builds.
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	DLA-4807-1
Debian Bugs	1148665

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
expat (PTS)	bookworm	2.5.0-1+deb12u2	vulnerable
	bookworm (security)	2.5.0-1+deb12u4	fixed
	trixie (security), trixie	2.8.3-1~deb13u1	vulnerable
	forky	2.8.4-2	fixed
	sid	2.9.0-1	fixed

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

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
expat	source	bookworm	2.5.0-1+deb12u4		DLA-4807-1
expat	source	(unstable)	2.8.4-2			1148665

Notes

https://github.com/libexpat/libexpat/pull/1282
Fixed by: https://github.com/libexpat/libexpat/commit/0cfd15bdf4b2c22d6b0df73610709dfb60921091 (R_2_8_5)
Fixed by: https://github.com/libexpat/libexpat/commit/28fcfba540f6933aa8904a1514c4811713d2ab72 (R_2_8_5)