CVE-2021-43848

Name	CVE-2021-43848
Description	h2o is an open source http server. In code prior to the `8c0eca3` commit h2o may attempt to access uninitialized memory. When receiving QUIC frames in certain order, HTTP/3 server-side implementation of h2o can be misguided to treat uninitialized memory as HTTP/3 frames that have been received. When h2o is used as a reverse proxy, an attacker can abuse this vulnerability to send internal state of h2o to backend servers controlled by the attacker or third party. Also, if there is an HTTP endpoint that reflects the traffic sent from the client, an attacker can use that reflector to obtain internal state of h2o. This internal state includes traffic of other connections in unencrypted form and TLS session tickets. This vulnerability exists in h2o server with HTTP/3 support, between commit 93af138 and d1f0f65. None of the released versions of h2o are affected by this vulnerability. There are no known workarounds. Users of unreleased versions of h2o using HTTP/3 are advised to upgrade immediately.
Source	CVE (at NVD; CERT, LWN, oss-sec, fulldisc, 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
h2o (PTS)	buster (security), buster, buster (lts)	2.2.5+dfsg2-2+deb10u2	fixed
	bullseye	2.2.5+dfsg2-6	fixed
	bookworm	2.2.5+dfsg2-7	fixed
	sid, trixie	2.2.5+dfsg2-9	fixed

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

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
h2o	source	(unstable)	(not affected)

Notes

- h2o <not-affected> (Vulnerable code not yet uploaded)
https://github.com/h2o/h2o/security/advisories/GHSA-f9xw-j925-m4m4
Introduced by: https://github.com/h2o/h2o/commit/93af1383b248e9284ba5f63211b4fbb4c828d060
Fixed by: https://github.com/h2o/h2o/commit/8c0eca3d9bc1f08e7c6bdf57645f3d54aed7d844