Mattermost Desktop App fails to restrict the allow list of domains which NTLM credentials are passed

{
  "id": "fc60160114f8545062916f752b2b1cb4fed7a40eb854557272693e5f52120c06",
  "url": "https://osv.dev/vulnerability/CVE-2026-6517",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Mattermost Desktop App fails to restrict the allow list of domains which NTLM credentials are passed",
    "summary": "Mattermost Desktop App versions <=6.1 5.5.13.0 fail to restrict the allow list of domains to which NTLM credentials were forwarded to in the Mattermost Desktop App which allows any user on a server without the image proxy enabled to intercept other users credentials via embedding an image that routes to an external web server. Mattermost Advisory ID: MMSA-2026-00651",
    "evidence": "osv:CVE-2026-6517",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-6517",
      "aliases": [
        "CVE-2026-6517"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/mattermost/desktop",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "last_affected": "f541b0cfdda853f51446582f7e1103c0f918a743"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:mattermost:mattermost_desktop:*:-:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "last_affected": "5.13.0"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v5.13.0-mas.1",
            "v5.13.0",
            "v5.13.0-rc.1",
            "v4.7.0-beta2",
            "beta2",
            "4.7.0-beta",
            "v1.3.0-rc2",
            "v1.3.0",
            "v1.3.0-rc1",
            "v1.2.0",
            "v1.1.1",
            "v1.1.0",
            "v1.0.7",
            "v1.0.6",
            "v1.0.5",
            "v1.0.4",
            "v1.0.3",
            "v1.0.2",
            "v1.0.1",
            "v1.0.0",
            "v0.5.1",
            "v0.5.0",
            "v0.4.0",
            "v0.3.0",
            "v0.2.0",
            "v0.1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-6517.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:52.752687046Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/6xxx/CVE-2026-6517.json",
        "https://mattermost.com/security-updates",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-6517"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-522"
        ],
        "cna_assigner": "Mattermost",
        "unresolved_ranges": [
          {
            "extracted_events": [
              {
                "range": [
                  {
                    "last_affected": "5.5.13"
                  }
                ],
                "source": "AFFECTED_FIELD",
                "strategy": "StandardRange"
              }
            ]
          }
        ],
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/6xxx/CVE-2026-6517.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-6517",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 521787,
  "published_at": "2026-06-15T13:55:25.742+00:00"
}