CVE-2026-3706 mkj Dropbear S Range Check curve25519.c unpackneg signature verification
A theoretical signature malleability flaw in Dropbear's curve25519 implementation could allow bypassing signature verification, though it is currently considered unexploitable in SSH.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-3706?
CVE-2026-3706 is a medium-severity vulnerability in mkj Dropbear, published on 8 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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."
Which versions are affected by CVE-2026-3706?
How do I fix CVE-2026-3706?
Apply the vendor's patch.
Is CVE-2026-3706 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-3706 exists.
Sources
Also known as DEBIAN-CVE-2026-3706, GHSA-87g2-jprq-4cmc, UBUNTU-CVE-2026-3706.