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CVE-2026-9816

🗓️ 17 Aug 2026 22:05:24Reported by MattermostType 
cve
 cve
🔗 web.nvd.nist.gov👁 80 Views🌐 WEB

Mattermost 10.11.x to 11.8.x lacks server-side validation of BoardMember.Scheme* fields, enabling privilege escalation via board member endpoints.

Related
Detection
Affected
Refs
Paths
NVD
Vulners
Node
OR
mattermostmattermost_serverRange10.11.0–10.11.22
mattermostmattermost_serverRange11.7.0–11.7.7
mattermostmattermost_serverRange11.8.0–11.8.4
[
  {
    "defaultStatus": "unaffected",
    "product": "Mattermost",
    "vendor": "Mattermost",
    "versions": [
      {
        "lessThanOrEqual": "11.7.6",
        "status": "affected",
        "version": "11.7.0",
        "versionType": "semver"
      },
      {
        "lessThanOrEqual": "10.11.21",
        "status": "affected",
        "version": "10.11.0",
        "versionType": "semver"
      },
      {
        "lessThanOrEqual": "11.8.3",
        "status": "affected",
        "version": "11.8.0",
        "versionType": "semver"
      },
      {
        "version": "11.9.0",
        "status": "unaffected"
      },
      {
        "version": "11.7.7",
        "status": "unaffected"
      },
      {
        "version": "10.11.22",
        "status": "unaffected"
      },
      {
        "version": "11.8.4",
        "status": "unaffected"
      }
    ]
  }
]
ParameterPositionPathDescriptionCWE
BoardMember.Schemerequest body/api/v2/boards/{boardID}/membersBoardMember.Scheme fields are not validated on insert, allowing a board editor or non-guest team member to grant board admin to arbitrary users via the endpoint.CWE-863
BoardMember.Schemerequest body/api/v2/teams/{teamID}/archive/importBoardMember.Scheme fields are not validated during archive import, enabling privilege escalation to board admin via the archive import flow.CWE-863

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19 Aug 2026 13:29Current
5.5Medium risk
Vulners AI Score5.5
CVSS 3.18.3
EPSS0.0035
SSVC
80