Unknown severity · Source severity not reportedCVE-2026-109553

Gitea SSH certificate principal impersonation of other usersCVE-2026-109553

Answer in brief

CVE-2026-109553 records a Unknown severity vulnerability in Gitea SSH certificate principal impersonation of other users. The current sources do not mark it as known exploited. The current feed maps Gitea/Gitea (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 18, 2026Updated Oct 18, 2026Source checked Oct 18, 2026First seen by HOL Oct 18, 2026Material review Oct 18, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Gitea/Gitea (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Gitea/Giteageneric	>=0 <=28.1.0	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Gitea/Gitea.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Oct 18, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 18, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Oct 18, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.