NodeBB - ActivityPub Author Spoofing via Unvalidated attributedTo Mapped to Local User

{
  "id": "edd2f6f5c12846932b28071b6baefb7e0e96a7b0f4a94a97a39b59b28d3728f5",
  "url": "https://osv.dev/vulnerability/CVE-2026-58593",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "NodeBB - ActivityPub Author Spoofing via Unvalidated attributedTo Mapped to Local User",
    "summary": "NodeBB does not bind the claimed author of an inbound ActivityPub object to the authenticated remote actor. The inbound middleware verifies the HTTP-signature actor and checks the origin of object.id, but never validates that attributedTo corresponds to the sender. In the object mock, attributedTo is used directly as a uid, and actors.assert silently ignores numeric identifiers (filtering them out without re-deriving the uid), so a federated remote actor can set attributedTo to a bare numeric value such as 1 and have the resulting post or private message created with that local uid as author, including the administrator account. This lets a remote attacker forge posts and direct messages attributed to arbitrary local users. Requires the ActivityPub/federation feature to be enabled.",
    "evidence": "osv:CVE-2026-58593",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-58593",
      "aliases": [
        "CVE-2026-58593"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/nodebb/nodebb",
              "type": "GIT",
              "events": [
                {
                  "introduced": "c17e7102fb6abcc25d346efa2600fcbbbee9ab04"
                },
                {
                  "last_affected": "c17e7102fb6abcc25d346efa2600fcbbbee9ab04"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "4.13.2"
                      },
                      {
                        "last_affected": "4.13.2"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandaloneSingleVersion"
                  },
                  {
                    "cpe": "cpe:2.3:a:nodebb:nodebb:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "last_affected": "4.13.2"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "4.13.2",
            "v4.13.2"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-58593.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:23.383695307Z",
      "provider": "osv",
      "references": [
        "https://github.com/NodeBB/NodeBB/blob/v4.13.2/src/activitypub/mocks.js",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/58xxx/CVE-2026-58593.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-58593",
        "https://www.vulncheck.com/advisories/nodebb-activitypub-author-spoofing-via-unvalidated-attributedto-mapped-to-local-user",
        "https://github.com/bikini/exploitarium/tree/main/nodebb-activitypub-attributedto-local-uid-spoof-poc"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-290",
          "CWE-345"
        ],
        "cna_assigner": "VulnCheck",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/58xxx/CVE-2026-58593.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-58593",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 489556,
  "published_at": "2026-07-01T19:27:23.367+00:00"
}