{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "last_affected": "28.1.0"
              }
            ],
            "source": "AFFECTED_FIELD"
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "4ebd5e319b6a9e629bfd7a04292a6fe85b08dee9"
            }
          ],
          "repo": "https://github.com/go-gitea/gitea",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-vcp6-2qc6-gvq3"
  ],
  "database_specific": {
    "cna_assigner": "Gitea",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/109xxx/CVE-2026-109553.json"
  },
  "details": "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.",
  "id": "CVE-2026-109553",
  "modified": "2026-10-20T10:30:44.777770573Z",
  "published": "2026-10-18T18:51:31.037Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://blog.gitea.com/release-of-28.2.0/"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/109xxx/CVE-2026-109553.json"
    },
    {
      "type": "FIX",
      "url": "https://github.com/go-gitea/gitea/pull/39839"
    },
    {
      "type": "FIX",
      "url": "https://github.com/go-gitea/gitea/pull/39847"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/go-gitea/gitea/releases/tag/v28.2.0"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/go-gitea/gitea/security/advisories/GHSA-vcp6-2qc6-gvq3"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-109553"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Gitea SSH certificate principal impersonation of other users"
}