CVE-2026-63115

{
  "id": "CVE-2026-63115",
  "sourceIdentifier": "[email protected]",
  "published": "2026-10-30T22:16:57.963",
  "lastModified": "2026-10-30T22:16:57.963",
  "vulnStatus": "Received",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "ActivityPub is a multi-tenant ActivityPub server for Ghost, built with Fedify. From 1.0.0 until 1.2.6, the `Undo` handler allows a remote federated server to cause the service to act on a `follow` or `repost` as though the activity came from a different account. This permits removal of an existing `follow` relationship or `repost` belonging to another account without that account's involvement. No private data is exposed and content is not modified; the affected relationships can be re-established. Services proxying to Ghost's hosted ActivityPub server have already been updated, while self-hosted services require an updated image and redeployment. This issue is fixed in version 1.2.6."
    }
  ],
  "affected": [
    {
      "source": "[email protected]",
      "affectedData": [
        {
          "vendor": "TryGhost",
          "product": "ActivityPub",
          "versions": [
            {
              "version": ">= 1.0.0, < 1.2.6",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV31": [
      {
        "source": "[email protected]",
        "type": "Secondary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
          "baseScore": 5.3,
          "baseSeverity": "MEDIUM",
          "attackVector": "NETWORK",
          "attackComplexity": "LOW",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "NONE",
          "integrityImpact": "LOW",
          "availabilityImpact": "NONE"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 1.4
      }
    ]
  },
  "weaknesses": [
    {
      "source": "[email protected]",
      "type": "Primary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-290"
        },
        {
          "lang": "en",
          "value": "CWE-345"
        },
        {
          "lang": "en",
          "value": "CWE-863"
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://github.com/TryGhost/ActivityPub/commit/1526f540b983da97750b380868a210e6cdfb985e",
      "source": "[email protected]"
    },
    {
      "url": "https://github.com/TryGhost/ActivityPub/pull/1929",
      "source": "[email protected]"
    },
    {
      "url": "https://github.com/TryGhost/ActivityPub/releases/tag/v1.2.6",
      "source": "[email protected]"
    },
    {
      "url": "https://github.com/TryGhost/ActivityPub/security/advisories/GHSA-mm4q-93gr-5mwc",
      "source": "[email protected]"
    }
  ]
}