CVE-2026-3706

Name	CVE-2026-3706
Description	A vulnerability was determined in mkj Dropbear up to 2025.89. Impacted is the function unpackneg of the file src/curve25519.c of the component S Range Check. This manipulation causes improper verification of cryptographic signature. The attack can be initiated remotely. The attack is considered to have high complexity. The exploitability is considered difficult. The actual existence of this vulnerability is currently in question. Patch name: fdec3c90a15447bd538641d85e5a3e3ac981011d. To fix this issue, it is recommended to deploy a patch. The project maintainer explains: "Signature Malleability is not exploitable in SSH protocol. (...) [A] PoC doesn't exist for SSH implementation, but rather it's against the internal API."
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	1130870

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
dropbear (PTS)	bullseye	2020.81-3+deb11u2	vulnerable
	bullseye (security)	2020.81-3+deb11u3	vulnerable
	bookworm	2022.83-1+deb12u3	vulnerable
	trixie (security), trixie	2025.89-1~deb13u1	vulnerable
	forky, sid	2025.89-1	vulnerable

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

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
dropbear	source	(unstable)	(unfixed)	unimportant		1130870

Notes

https://github.com/mkj/dropbear/issues/406
https://github.com/mkj/dropbear/pull/407
No security impact:
https://github.com/mkj/dropbear/issues/406#issuecomment-4064502613