CVE-2026-31958

Name	CVE-2026-31958
Description	Tornado is a Python web framework and asynchronous networking library. In versions of Tornado prior to 6.5.5, the only limit on the number of parts in multipart/form-data is the max_body_size setting (default 100MB). Since parsing occurs synchronously on the main thread, this creates the possibility of denial-of-service due to the cost of parsing very large multipart bodies with many parts. This vulnerability is fixed in 6.5.5.
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-4520-1
Debian Bugs	1130507

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
python-tornado (PTS)	bullseye	6.1.0-1	vulnerable
	bullseye (security)	6.1.0-1+deb11u4	fixed
	bookworm, bookworm (security)	6.2.0-3+deb12u2	vulnerable
	trixie	6.4.2-3	vulnerable
	forky	6.5.4-1	vulnerable
	sid	6.5.5-1	fixed

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

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
python-tornado	source	bullseye	6.1.0-1+deb11u4		DLA-4520-1
python-tornado	source	(unstable)	6.5.5-1			1130507

Notes

https://github.com/tornadoweb/tornado/security/advisories/GHSA-qjxf-f2mg-c6mc
Fixed by: https://github.com/tornadoweb/tornado/commit/119a195e290c43ad2d63a2cf012c29d43d6ed839 (v6.5.5)