CVE-2026-115927

Name	CVE-2026-115927
Description	Tornado is a Python web framework and asynchronous networking library. Prior to 6.6.0, Tornado decodes HTTP/1.1 chunked transfer encoding by processing body data that has already arrived without yielding to the event loop. A remote unauthenticated peer can send millions of one-byte chunks to monopolize the process event loop and stall every other connection served by that process, while lowering max_body_size only limits the duration of each request. For handlers that do not use @stream_request_body, retaining each chunk as a separate object can consume roughly twenty times the received body size, and SimpleAsyncHTTPClient has the same event-loop behavior when reading a response from a malicious server. This issue is fixed in version 6.6.0.
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	1152300

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
python-tornado (PTS)	bookworm, bookworm (security)	6.2.0-3+deb12u4	vulnerable
	trixie (security), trixie	6.4.2-3+deb13u2	vulnerable
	forky, sid	6.5.5-5	vulnerable

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

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
python-tornado	source	(unstable)	(unfixed)			1152300

Notes

https://github.com/tornadoweb/tornado/security/advisories/GHSA-r4j5-9xpp-3985
https://github.com/tornadoweb/tornado/pull/3773
Fixed by: https://github.com/tornadoweb/tornado/commit/ceab33581489751a66fba8566ad6d5960d4b01c8 (v6.6.0b1)