Vulnerability-Lookup

FKIE_CVE-2026-8821

Vulnerability from fkie_nvd - Published: 2026-09-14 11:17 - Updated: 2026-09-16 19:30

Severity

7.1 (High) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N

Summary

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrary user to a restricted channel via the run owner field.. Mattermost Advisory ID: MMSA-2026-00677

References

	URL	Tags
	responsibledisclosure@mattermost.com	https://mattermost.com/security-updates

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Mattermost",
          "vendor": "Mattermost",
          "versions": [
            {
              "lessThanOrEqual": "11.9.0",
              "status": "affected",
              "version": "11.9.0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "11.8.4",
              "status": "affected",
              "version": "11.8.0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "11.7.7",
              "status": "affected",
              "version": "11.7.0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "10.11.22",
              "status": "affected",
              "version": "10.11.0",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "11.10.0"
            },
            {
              "status": "unaffected",
              "version": "11.9.1"
            },
            {
              "status": "unaffected",
              "version": "11.8.5"
            },
            {
              "status": "unaffected",
              "version": "11.7.8"
            },
            {
              "status": "unaffected",
              "version": "10.11.23"
            }
          ]
        }
      ],
      "source": "responsibledisclosure@mattermost.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Mattermost versions 11.9.x \u003c= 11.9.0, 11.8.x \u003c= 11.8.4, 11.7.x \u003c= 11.7.7, 10.11.x \u003c= 10.11.22 fail to validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrary user to a restricted channel via the run owner field.. Mattermost Advisory ID: MMSA-2026-00677"
    }
  ],
  "id": "CVE-2026-8821",
  "lastModified": "2026-09-16T19:30:49.967",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 7.1,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "LOW",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 4.2,
        "source": "responsibledisclosure@mattermost.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-8821",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-09-14T11:03:09.855978Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-09-14T11:17:06.153",
  "references": [
    {
      "source": "responsibledisclosure@mattermost.com",
      "url": "https://mattermost.com/security-updates"
    }
  ],
  "sourceIdentifier": "responsibledisclosure@mattermost.com",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-862"
        }
      ],
      "source": "responsibledisclosure@mattermost.com",
      "type": "Secondary"
    }
  ]
}

CVE-2026-8821 (GCVE-0-2026-8821)

Vulnerability from cvelistv5 – Published: 2026-09-14 10:42 – Updated: 2026-09-14 11:19

Title

Playbooks run owner channel membership permission bypass

Summary

Severity

7.1 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-14 11:03 UTC

CWE

CWE-862 - Missing Authorization

Assigner

Mattermost mitre root

References

1 reference

URL	Tags
https://mattermost.com/security-updates	vendor-advisory

Impacted products

1 product

Vendor	Product	Version
Mattermost	Mattermost	Affected: 11.9.0 , ≤ 11.9.0 (semver) Affected: 11.8.0 , ≤ 11.8.4 (semver) Affected: 11.7.0 , ≤ 11.7.7 (semver) Affected: 10.11.0 , ≤ 10.11.22 (semver) Unaffected: 11.10.0 Unaffected: 11.9.1 Unaffected: 11.8.5 Unaffected: 11.7.8 Unaffected: 10.11.23

Credits

ilent0

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-8821",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-09-14T11:03:09.855978Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-09-14T11:19:44.842Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Mattermost",
          "vendor": "Mattermost",
          "versions": [
            {
              "lessThanOrEqual": "11.9.0",
              "status": "affected",
              "version": "11.9.0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "11.8.4",
              "status": "affected",
              "version": "11.8.0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "11.7.7",
              "status": "affected",
              "version": "11.7.0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "10.11.22",
              "status": "affected",
              "version": "10.11.0",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "11.10.0"
            },
            {
              "status": "unaffected",
              "version": "11.9.1"
            },
            {
              "status": "unaffected",
              "version": "11.8.5"
            },
            {
              "status": "unaffected",
              "version": "11.7.8"
            },
            {
              "status": "unaffected",
              "version": "10.11.23"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "ilent0"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Mattermost versions 11.9.x \u003c= 11.9.0, 11.8.x \u003c= 11.8.4, 11.7.x \u003c= 11.7.7, 10.11.x \u003c= 10.11.22 fail to validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrary user to a restricted channel via the run owner field.. Mattermost Advisory ID: MMSA-2026-00677"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 7.1,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "LOW",
            "privilegesRequired": "LOW",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-862",
              "description": "CWE-862: Missing Authorization",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-14T10:42:42.672Z",
        "orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee",
        "shortName": "Mattermost"
      },
      "references": [
        {
          "name": "MMSA-2026-00677",
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://mattermost.com/security-updates"
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "value": "Update Mattermost to versions 11.10.0, 11.9.1, 11.8.5, 11.7.8, 10.11.23 or higher."
        }
      ],
      "source": {
        "advisory": "MMSA-2026-00677",
        "defect": [
          "https://mattermost.atlassian.net/browse/MM-68695"
        ],
        "discovery": "EXTERNAL"
      },
      "title": "Playbooks run owner channel membership permission bypass",
      "x_generator": {
        "engine": "cvelib 1.8.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee",
    "assignerShortName": "Mattermost",
    "cveId": "CVE-2026-8821",
    "datePublished": "2026-09-14T10:42:42.672Z",
    "dateReserved": "2026-05-18T09:19:00.475Z",
    "dateUpdated": "2026-09-14T11:19:44.842Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.