Discourse Vulnerable to Stored XSS via Shared AI Conversation Onebox

{
  "id": "0fed2ffb3f9486ac59bc4e3a2cbe7b46735c36be86be36aebb9fe6a8e2549d43",
  "url": "https://osv.dev/vulnerability/CVE-2026-27570",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Discourse Vulnerable to Stored XSS via Shared AI Conversation Onebox",
    "summary": "Discourse is an open-source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, the onebox method in the SharedAiConversation model renders the conversation title directly into HTML without proper sanitization. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain a patch. As a workaround, tighten access by changing the `ai_bot_public_sharing_allowed_groups` site setting.",
    "evidence": "osv:CVE-2026-27570",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-27570",
      "aliases": [
        "BIT-discourse-2026-27570",
        "CVE-2026-27570",
        "GHSA-hfxw-89hw-vwmv"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/discourse/discourse",
              "type": "GIT",
              "events": [
                {
                  "introduced": "322d3c0ac6a8f133b3f82875e9dbbe310f638c1b"
                },
                {
                  "fixed": "808b2ac23d8ff421563b40203091026732471c60"
                },
                {
                  "introduced": "f7cec86997edc21d6074ceb7666f7e2e6e1b1fdf"
                },
                {
                  "fixed": "f38464e46df1b8c51f7d60826502476908d6bb2b"
                },
                {
                  "introduced": "896e810e1b296478bba91559a8fc89a9926f11fe"
                },
                {
                  "fixed": "43a5a60b595f0120e6adfc131f2408508fe341f1"
                },
                {
                  "fixed": "c14f8f52b7999328bd9f8665f2ecfa24dadc4bf1"
                },
                {
                  "fixed": "f2aafa5c7467c94fcd4ebd36785a98e77ca088cc"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "2026.1.0"
                      },
                      {
                        "fixed": "2026.1.2"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "2026.2.0"
                      },
                      {
                        "fixed": "2026.2.1"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:discourse:discourse:2026.3.0:*:*:*:latest:*:*:*",
                    "range": [
                      {
                        "introduced": "2026.3.0"
                      },
                      {
                        "last_affected": "2026.3.0"
                      }
                    ],
                    "source": "CPE_STRING"
                  },
                  {
                    "range": [
                      {
                        "fixed": "43a5a60b595f0120e6adfc131f2408508fe341f1"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "c14f8f52b7999328bd9f8665f2ecfa24dadc4bf1"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "f2aafa5c7467c94fcd4ebd36785a98e77ca088cc"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "2026.3.0",
            "= 2026.3.0-latest",
            "v2026.1.1",
            "v2026.2.0",
            "v2026.3.0-latest",
            "v2026.1.0",
            "stable",
            "esr",
            "v2026.2.0-latest",
            "v2026.1.0-latest"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-27570.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:23.488141131Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27570.json",
        "https://github.com/discourse/discourse/security/advisories/GHSA-hfxw-89hw-vwmv",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-27570",
        "https://github.com/discourse/discourse/commit/43a5a60b595f0120e6adfc131f2408508fe341f1",
        "https://github.com/discourse/discourse/commit/c14f8f52b7999328bd9f8665f2ecfa24dadc4bf1",
        "https://github.com/discourse/discourse/commit/f2aafa5c7467c94fcd4ebd36785a98e77ca088cc"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-79"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27570.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-27570",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 489942,
  "published_at": "2026-03-19T20:52:17.572+00:00"
}