CVE-2026-109553
Gitea SSH certificate principal impersonation of other users
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.
INFO
Published Date :
Oct. 18, 2026, 7:16 p.m.
Last Modified :
Oct. 18, 2026, 7:16 p.m.
Remotely Exploit :
No
Source :
88ee5874-cf24-4952-aea0-31affedb7ff2
Solution
- Configure SSH_TRUSTED_USER_CA_KEYS correctly.
- Avoid setting SSH_AUTHORIZED_PRINCIPALS_ALLOW to 'anything'.
- Review and limit principals in SSH certificates.
- Apply Gitea updates when available.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-109553.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-109553 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-109553
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-109553 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-109553 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by 88ee5874-cf24-4952-aea0-31affedb7ff2
Oct. 18, 2026
Action Type Old Value New Value Added 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. Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/109xxx/CVE-2026-109553.json">CVE-2026-109553</a> Added Reference https://blog.gitea.com/release-of-28.2.0/ Added Reference https://github.com/go-gitea/gitea/pull/39839 Added Reference https://github.com/go-gitea/gitea/pull/39847 Added Reference https://github.com/go-gitea/gitea/releases/tag/v28.2.0 Added Reference https://github.com/go-gitea/gitea/security/advisories/GHSA-vcp6-2qc6-gvq3