CVE-2021-36369

Name	CVE-2021-36369
Description	An issue was discovered in Dropbear through 2020.81. Due to a non-RFC-compliant check of the available authentication methods in the client-side SSH code, it is possible for an SSH server to change the login process in its favor. This attack can bypass additional security measures such as FIDO2 tokens or SSH-Askpass. Thus, it allows an attacker to abuse a forwarded agent for logging on to another server unnoticed.
Source	CVE (at NVD; CERT, LWN, oss-sec, fulldisc, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
References	DLA-3187-1

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
dropbear (PTS)	jessie, jessie (lts)	2014.65-1+deb8u3	vulnerable
	stretch	2016.74-5+deb9u1	vulnerable
	buster (security), buster, buster (lts)	2018.76-5+deb10u2	fixed
	bullseye	2020.81-3+deb11u2	fixed
	bookworm	2022.83-1+deb12u2	fixed
	sid, trixie	2024.86-1	fixed

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

Package	Type	Release	Fixed Version	Urgency	Origin
dropbear	source	jessie	(unfixed)	end-of-life
dropbear	source	stretch	(unfixed)	end-of-life
dropbear	source	buster	2018.76-5+deb10u2		DLA-3187-1
dropbear	source	bullseye	2020.81-3+deb11u1
dropbear	source	(unstable)	2022.82-1

https://github.com/mkj/dropbear/pull/128
https://github.com/mkj/dropbear/commit/210a9833496ed2a93b8da93924874938127ce0b5 (DROPBEAR_2022.82)