GitLab Plugin Allows Non-Admin Users to Modify Default Instance Configuration

Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler, which allows any authenticated user to overwrite the global default GitLab instance configuration via the {{/gitlab connect <instance-name>}} slash command.. Mattermost Advisory ID: MMSA-2026-00644

Problem type

CWE-862: Missing Authorization

Affected products

Mattermost

Mattermost

<= 11.7.0 - AFFECTED

<= 11.6.2 - AFFECTED

<= 11.5.5 - AFFECTED

<= 10.11.17 - AFFECTED

11.8.0 - UNAFFECTED

11.7.1 - UNAFFECTED

11.6.3 - UNAFFECTED

11.5.6 - UNAFFECTED

10.11.18 - UNAFFECTED

References

MMSA-2026-00644

https://mattermost.com/security-updates

vendor-advisory

GitHub Security Advisories

GHSA-2g8v-grq3-hq2g

Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17...

https://github.com/advisories/GHSA-2g8v-grq3-hq2g

Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler, which allows any authenticated user to overwrite the global default GitLab instance configuration via the {{/gitlab connect }} slash command.. Mattermost Advisory ID: MMSA-2026-00644

nvd.nist.gov

https://nvd.nist.gov/vuln/detail/CVE-2026-5139

mattermost.com

https://mattermost.com/security-updates

github.com

https://github.com/advisories/GHSA-2g8v-grq3-hq2g

JSON source

https://cveawg.mitre.org/api/cve/CVE-2026-5139

Click to expand

{
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "cveMetadata": {
    "cveId": "CVE-2026-5139",
    "assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee",
    "assignerShortName": "Mattermost",
    "dateUpdated": "2026-06-22T13:34:21.247Z",
    "dateReserved": "2026-03-30T11:29:16.698Z",
    "datePublished": "2026-06-22T13:34:21.247Z",
    "state": "PUBLISHED"
  },
  "containers": {
    "cna": {
      "providerMetadata": {
        "orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee",
        "shortName": "Mattermost",
        "dateUpdated": "2026-06-22T13:34:21.247Z"
      },
      "title": "GitLab Plugin Allows Non-Admin Users to Modify Default Instance Configuration",
      "descriptions": [
        {
          "lang": "en",
          "value": "Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler, which allows any authenticated user to overwrite the global default GitLab instance configuration via the {{/gitlab connect <instance-name>}} slash command.. Mattermost Advisory ID: MMSA-2026-00644"
        }
      ],
      "affected": [
        {
          "vendor": "Mattermost",
          "product": "Mattermost",
          "defaultStatus": "unaffected",
          "versions": [
            {
              "version": "11.7.0",
              "status": "affected",
              "versionType": "semver",
              "lessThanOrEqual": "11.7.0"
            },
            {
              "version": "11.6.0",
              "status": "affected",
              "versionType": "semver",
              "lessThanOrEqual": "11.6.2"
            },
            {
              "version": "11.5.0",
              "status": "affected",
              "versionType": "semver",
              "lessThanOrEqual": "11.5.5"
            },
            {
              "version": "10.11.0",
              "status": "affected",
              "versionType": "semver",
              "lessThanOrEqual": "10.11.17"
            },
            {
              "version": "11.8.0",
              "status": "unaffected"
            },
            {
              "version": "11.7.1",
              "status": "unaffected"
            },
            {
              "version": "11.6.3",
              "status": "unaffected"
            },
            {
              "version": "11.5.6",
              "status": "unaffected"
            },
            {
              "version": "10.11.18",
              "status": "unaffected"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "lang": "en",
              "description": "CWE-862: Missing Authorization",
              "cweId": "CWE-862",
              "type": "CWE"
            }
          ]
        }
      ],
      "references": [
        {
          "url": "https://mattermost.com/security-updates",
          "name": "MMSA-2026-00644",
          "tags": [
            "vendor-advisory"
          ]
        }
      ],
      "metrics": [
        {
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ],
          "cvssV3_1": {
            "version": "3.1",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L",
            "attackVector": "NETWORK",
            "attackComplexity": "LOW",
            "privilegesRequired": "LOW",
            "userInteraction": "NONE",
            "scope": "UNCHANGED",
            "confidentialityImpact": "NONE",
            "integrityImpact": "LOW",
            "availabilityImpact": "LOW",
            "baseScore": 5.4,
            "baseSeverity": "MEDIUM"
          }
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "value": "Update Mattermost to versions 11.8.0, 11.7.1, 11.6.3, 11.5.6, 10.11.18 or higher."
        }
      ],
      "credits": [
        {
          "lang": "en",
          "value": "hunterxluxhug",
          "type": "finder"
        }
      ]
    }
  }
}