Mattermost thread memberships persist after team removal, exposing private channel thread metadata on re-invite

{
  "id": "41d8ce4a7c680c7b552d5e0b87cf26adcb142b165a6f7864bdf3b6a9cbdff903",
  "url": "https://osv.dev/vulnerability/CVE-2026-9693",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Mattermost thread memberships persist after team removal, exposing private channel thread metadata on re-invite",
    "summary": "Mattermost versions 10.11.x <= 10.11.20, 11.7.x <= 11.7.5 Mattermost fails to remove thread membership records when a user is removed from or leaves a team, which allows a previously removed user who is later re-invited to the team to view private channel thread root post content and metadata via the team threads API.. Mattermost Advisory ID: MMSA-2026-00682",
    "evidence": "osv:CVE-2026-9693",
    "products": [],
    "severity": "low",
    "structured": {
      "id": "CVE-2026-9693",
      "aliases": [
        "CVE-2026-9693"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/mattermost/mattermost",
              "type": "GIT",
              "events": [
                {
                  "introduced": "5b955468ea1ea8b56c0fb10feb258a36a767d7bb"
                },
                {
                  "fixed": "638007314e9dde1575d3caa167e1067b1c577204"
                },
                {
                  "introduced": "a9e574a82633915f22071f0d7ca2b006f249ec2a"
                },
                {
                  "fixed": "3e198e4d5518c09836ea4c8e7ac7201c83aab67b"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "10.11.0"
                      },
                      {
                        "fixed": "10.11.21"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "11.7.0"
                      },
                      {
                        "fixed": "11.7.6"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v11.7.5-rc1",
            "v11.7.5",
            "v11.7.4",
            "v11.7.3",
            "v10.11.20",
            "v10.11.19",
            "v10.11.19-rc1",
            "v11.7.2",
            "v10.11.18",
            "v11.7.1",
            "v10.11.17",
            "v10.11.16",
            "v11.7.0",
            "mattermost-redux@11.7.0",
            "@mattermost/types@11.7.0",
            "@mattermost/shared@11.7.0",
            "@mattermost/client@11.7.0",
            "v10.11.15-rc1",
            "v10.11.15",
            "v10.11.14",
            "v10.11.14-rc1",
            "v10.11.13",
            "v10.11.13-rc1",
            "v10.11.12",
            "v10.11.11-rc2",
            "v10.11.11",
            "v10.11.11-rc1",
            "v10.11.10",
            "v10.11.9",
            "v10.11.9-rc1",
            "v10.11.8",
            "v10.11.7",
            "v10.11.6",
            "v10.11.5",
            "v10.11.4-rc3",
            "v10.11.4",
            "v10.11.4-rc2",
            "v10.11.4-rc1",
            "v10.11.3",
            "v10.11.2-rc2",
            "v10.11.2",
            "v10.11.2-rc1",
            "v10.11.1",
            "v10.11.1-rc1",
            "v10.11.0-rc3",
            "v10.11.0",
            "mattermost-redux@10.11.0",
            "@mattermost/types@10.11.0",
            "@mattermost/client@10.11.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-9693.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:40.420322640Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/9xxx/CVE-2026-9693.json",
        "https://mattermost.com/security-updates",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-9693"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-459"
        ],
        "cna_assigner": "Mattermost",
        "unresolved_ranges": [
          {
            "extracted_events": [
              {
                "range": [
                  {
                    "introduced": "10.11.0"
                  },
                  {
                    "last_affected": "10.11.20"
                  },
                  {
                    "introduced": "11.7.0"
                  },
                  {
                    "last_affected": "11.7.5"
                  }
                ],
                "source": "AFFECTED_FIELD",
                "strategy": "StandardRange"
              }
            ]
          }
        ],
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/9xxx/CVE-2026-9693.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-9693",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 508188,
  "published_at": "2026-08-17T22:07:12.958+00:00"
}