CVE-2026-66338

Name	CVE-2026-66338
Description	A flaw was found in libsoup. The chunked transfer encoding parser uses a permissive parsing function for chunk sizes that silently accepts inputs violating RFC 9112, including leading whitespace, plus sign prefixes, and trailing invalid characters. When libsoup operates behind a strict frontend proxy, this parsing differential can be exploited to smuggle HTTP requests.
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)

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
libsoup2.4 (PTS)	bullseye	2.72.0-2	vulnerable
	bullseye (security)	2.72.0-2+deb11u3	vulnerable
	bookworm	2.74.3-1+deb12u1	vulnerable
	trixie	2.74.3-10.1	vulnerable
libsoup3 (PTS)	bookworm	3.2.3-0+deb12u2	vulnerable
	trixie	3.6.5-3	vulnerable
	forky, sid	3.6.6-1	vulnerable

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

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
libsoup2.4	source	(unstable)	(unfixed)
libsoup3	source	(unstable)	(unfixed)

https://bugzilla.redhat.com/show_bug.cgi?id=2506950
https://gitlab.gnome.org/GNOME/libsoup/-/work_items/533