CVE-2026-109553 Gitea SSH certificate principal impersonation of other users
Attackers can impersonate other users via SSH certificate principal spoofing when specific trusted CA and principal settings are enabled.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-109553?
CVE-2026-109553 is a high-severity authentication bypass vulnerability in Gitea, published on 18 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Gitea resolved the principals of an SSH certificate by searching the content of all stored public keys instead of only principal keys. When Gitea trusts a user certificate authority (`SSH_TRUSTED_USER_CA_KEYS`) and accepts arbitrary principals (`SSH_AUTHORIZED_PRINCIPALS_ALLOW=anything`), a user could register another user's public key line as their own principal, or a holder of a certificate signed by that authority could list it, and then authenticate as the owner of that key through the HTTP signature API and the built-in SSH server. Instances that do not trust a user certificate authority are not affected.
Which versions are affected by CVE-2026-109553?
How do I fix CVE-2026-109553?
No fix has been published for CVE-2026-109553 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-109553 being exploited?
There is no known exploitation of CVE-2026-109553 in the wild and no public exploit code.
Sources
Also known as GHSA-vcp6-2qc6-gvq3.