CVE-2026-6689: Github.com/mattermost/mattermost server Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-c28q-m4gf-vg4q",
  "modified" : "2026-08-24T21:35:43Z",
  "published" : "2026-06-12T18:31:59Z",
  "aliases" : [ "CVE-2026-6689" ],
  "summary" : "Mattermost doesn't enforce PermissionInviteUser when setting AllowOpenInvite or AllowedDomains during team creation",
  "details" : "Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 Fail to enforce PermissionInviteUser when setting AllowOpenInvite or AllowedDomains during team creation (the check was only applied on update/patch), which allows an authenticated user holding PermissionCreateTeam but not PermissionInviteUser on the resulting team to configure invite-controlled team settings (make the team publicly joinable via open invite and/or constrain membership via allowed domains) that they are not permitted to set on an existing team via POST /api/v4/teams with allow_open_invite: true and/or a non-empty allowed_domains in the request body.. Mattermost Advisory ID: MMSA-2026-00655",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "11.6.0"
      }, {
        "fixed" : "11.6.1"
      } ]
    } ],
    "versions" : [ "11.6.0" ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "11.5.0"
      }, {
        "fixed" : "11.5.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 11.5.4"
    }
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "10.11.0"
      }, {
        "fixed" : "10.11.17"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 10.11.15"
    }
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/mattermost/server/v8"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "8.0.0-20250731163400-5b955468ea1e"
      }, {
        "fixed" : "8.0.0-20260501144115-7d6816abdfd1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-6689"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36402"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36384"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36383"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36375"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/pull/36188"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/977c791e5b54bc14fdb96a2b3dacc85da5d8c623"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/7d6816abdfd170169f717aea43c5716a1f9ef6b0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/479fc42d0ec6da48e76b59608233d90bfc69769d"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/3a96344214b1a84df70d97052d46b6f2b40b0caa"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/commit/2dea05864024b3254fb28c5ed679592e2b7cd672"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/releases/tag/v10.11.16"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/releases/tag/v11.5.5"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/releases/tag/v11.6.2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mattermost/mattermost/releases/tag/v11.7.0"
  }, {
    "type" : "WEB",
    "url" : "https://mattermost.com/security-updates"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mattermost/mattermost"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-862" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-24T21:35:43Z",
    "nvd_published_at" : "2026-06-12T17:16:27Z"
  }
}