CVE-2026-109553 (GCVE-0-2026-109553)

Vulnerability from cvelistv5 – Published: 2026-10-18 18:51 – Updated: 2026-10-19 20:19
VLAI
Title
Gitea SSH certificate principal impersonation of other users
Summary
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.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-19 20:19 UTC
Assigner
Gitea CNA under the mitre root
CNA scorecard C 61/100 over 165 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Gitea Gitea Affected: 0 , ≤ 28.1.0 (semver)
guessed Create a notification for this product.
Credits
https://github.com/DshtAnger https://github.com/silverwind https://github.com/wxiaoguang https://github.com/bircni
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "cvssV3_1": {
              "attackComplexity": "HIGH",
              "attackVector": "NETWORK",
              "availabilityImpact": "HIGH",
              "baseScore": 7.5,
              "baseSeverity": "HIGH",
              "confidentialityImpact": "HIGH",
              "integrityImpact": "HIGH",
              "privilegesRequired": "LOW",
              "scope": "UNCHANGED",
              "userInteraction": "NONE",
              "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
              "version": "3.1"
            }
          },
          {
            "other": {
              "content": {
                "id": "CVE-2026-109553",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-10-19T20:19:01.147709Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-10-19T20:19:06.039Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "packageName": "gitea.dev",
          "product": "Gitea",
          "vendor": "Gitea",
          "versions": [
            {
              "lessThanOrEqual": "28.1.0",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "reporter",
          "value": "https://github.com/DshtAnger"
        },
        {
          "lang": "en",
          "type": "remediation developer",
          "value": "https://github.com/silverwind"
        },
        {
          "lang": "en",
          "type": "remediation developer",
          "value": "https://github.com/wxiaoguang"
        },
        {
          "lang": "en",
          "type": "remediation developer",
          "value": "https://github.com/bircni"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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\u0027s 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."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-18T18:51:31.037Z",
        "orgId": "88ee5874-cf24-4952-aea0-31affedb7ff2",
        "shortName": "Gitea"
      },
      "references": [
        {
          "name": "GitHub Security Advisory GHSA-vcp6-2qc6-gvq3",
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://github.com/go-gitea/gitea/security/advisories/GHSA-vcp6-2qc6-gvq3"
        },
        {
          "name": "Fix: go-gitea/gitea pull request #39839",
          "tags": [
            "patch"
          ],
          "url": "https://github.com/go-gitea/gitea/pull/39839"
        },
        {
          "name": "Fix backport to release/v28: go-gitea/gitea pull request #39847",
          "tags": [
            "patch"
          ],
          "url": "https://github.com/go-gitea/gitea/pull/39847"
        },
        {
          "name": "Gitea 28.2.0 release announcement",
          "tags": [
            "release-notes"
          ],
          "url": "https://blog.gitea.com/release-of-28.2.0/"
        },
        {
          "name": "go-gitea/gitea v28.2.0 release",
          "tags": [
            "release-notes"
          ],
          "url": "https://github.com/go-gitea/gitea/releases/tag/v28.2.0"
        }
      ],
      "title": "Gitea SSH certificate principal impersonation of other users"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "88ee5874-cf24-4952-aea0-31affedb7ff2",
    "assignerShortName": "Gitea",
    "cveId": "CVE-2026-109553",
    "datePublished": "2026-10-18T18:51:31.037Z",
    "dateReserved": "2026-10-14T20:08:45.856Z",
    "dateUpdated": "2026-10-19T20:19:06.039Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-109553",
      "date": "2026-10-20",
      "epss": "0.00198",
      "percentile": "0.08925"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "defaultStatus": "unaffected",
                "packageName": "gitea.dev",
                "product": "Gitea",
                "vendor": "Gitea",
                "versions": [
                  {
                    "lessThanOrEqual": "28.1.0",
                    "status": "affected",
                    "version": "0",
                    "versionType": "semver"
                  }
                ]
              }
            ],
            "source": "88ee5874-cf24-4952-aea0-31affedb7ff2"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "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\u0027s 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",
        "lastModified": "2026-10-19T21:17:04.780",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "HIGH",
                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 7.5,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 1.6,
              "impactScore": 5.9,
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "type": "Secondary"
            }
          ],
          "ssvcV203": [
            {
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "ssvcData": {
                "id": "CVE-2026-109553",
                "options": [
                  {
                    "exploitation": "none"
                  },
                  {
                    "automatable": "no"
                  },
                  {
                    "technicalImpact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-10-19T20:19:01.147709Z",
                "version": "2.0.3"
              }
            }
          ]
        },
        "published": "2026-10-18T19:16:32.997",
        "references": [
          {
            "source": "88ee5874-cf24-4952-aea0-31affedb7ff2",
            "url": "https://blog.gitea.com/release-of-28.2.0/"
          },
          {
            "source": "88ee5874-cf24-4952-aea0-31affedb7ff2",
            "url": "https://github.com/go-gitea/gitea/pull/39839"
          },
          {
            "source": "88ee5874-cf24-4952-aea0-31affedb7ff2",
            "url": "https://github.com/go-gitea/gitea/pull/39847"
          },
          {
            "source": "88ee5874-cf24-4952-aea0-31affedb7ff2",
            "url": "https://github.com/go-gitea/gitea/releases/tag/v28.2.0"
          },
          {
            "source": "88ee5874-cf24-4952-aea0-31affedb7ff2",
            "url": "https://github.com/go-gitea/gitea/security/advisories/GHSA-vcp6-2qc6-gvq3"
          }
        ],
        "sourceIdentifier": "88ee5874-cf24-4952-aea0-31affedb7ff2",
        "vulnStatus": "Awaiting Analysis"
      }
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.

Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

JSON

Loading timeline…




    Related by attack behaviour

    Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.