CVE-2026-109553 (CVSS 7.5)

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.

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CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0018

Probability of exploitation

0.07%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

References

Other References

https://blog.gitea.com/release-of-28.2.0/ https://github.com/go-gitea/gitea/pull/39839 https://github.com/go-gitea/gitea/pull/39847 https://github.com/go-gitea/gitea/releases/tag/v28.2.0 https://github.com/go-gitea/gitea/security/advisories/GHSA-vcp6-2qc6-gvq3

Frequently Asked Questions

What is CVE-2026-109553? +

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. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-109553? +

CVE-2026-109553 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0018, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-109553? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

CVE-2026-109553