Vulnerability-Lookup

GHSA-W9M8-P4CC-4QJ9

Vulnerability from github – Published: 2026-05-26 13:30 – Updated: 2026-06-29 22:52

Summary

Mattermost doesn't properly validate msgpack-encoded WebSocket frames before memory allocation

Details

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to properly validate msgpack-encoded WebSocket frames before memory allocation which allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users via a crafted binary WebSocket message sent to the public WebSocket endpoint.. Mattermost Advisory ID: MMSA-2026-00647

Severity

7.5 (High)


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

Show details on source website

JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/mattermost/mattermost-server"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "11.6.0"
            },
            {
              "fixed": "11.6.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "11.6.0"
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/mattermost/mattermost-server"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "11.5.0"
            },
            {
              "fixed": "11.5.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/mattermost/mattermost-server"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "11.4.0"
            },
            {
              "fixed": "11.4.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/mattermost/mattermost-server"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "10.11.0"
            },
            {
              "fixed": "10.11.15"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/mattermost/mattermost/server/v8"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "8.0.0-20260410202636-17939826efa2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-5740"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-789"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-29T22:52:00Z",
    "nvd_published_at": "2026-05-22T11:16:23Z",
    "severity": "HIGH"
  },
  "details": "Mattermost versions 11.6.x \u003c= 11.6.0, 11.5.x \u003c= 11.5.3, 11.4.x \u003c= 11.4.4, 10.11.x \u003c= 10.11.14 fail to properly validate msgpack-encoded WebSocket frames before memory allocation which allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users via a crafted binary WebSocket message sent to the public WebSocket endpoint.. Mattermost Advisory ID: MMSA-2026-00647",
  "id": "GHSA-w9m8-p4cc-4qj9",
  "modified": "2026-06-29T22:52:00Z",
  "published": "2026-05-26T13:30:15Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-5740"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mattermost/mattermost/commit/17939826efa20a97f087b3d390ec5136df350bae"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/mattermost/mattermost"
    },
    {
      "type": "WEB",
      "url": "https://mattermost.com/security-updates"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Mattermost doesn\u0027t properly validate msgpack-encoded WebSocket frames before memory allocation"
}

CVE-2026-5740 (GCVE-0-2026-5740)

Vulnerability from cvelistv5 – Published: 2026-05-22 10:22 – Updated: 2026-05-22 12:14

Title

Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server

Summary

Severity

7.5 (High)


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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-05-22 12:14 UTC

CWE

CWE-789 - Memory Allocation with Excessive Size Value

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: 11.6.0 , ≤ 11.6.0 (semver) Affected: 11.5.0 , ≤ 11.5.3 (semver) Affected: 11.4.0 , ≤ 11.4.4 (semver) Affected: 10.11.0 , ≤ 10.11.14 (semver) Unaffected: 11.7.0 Unaffected: 11.6.1 Unaffected: 11.5.4 Unaffected: 11.4.5 Unaffected: 10.11.15

Credits

ZephrFish

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-5740",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-05-22T12:14:18.991826Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-05-22T12:14:25.145Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
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    "cna": {
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          "defaultStatus": "unaffected",
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          "vendor": "Mattermost",
          "versions": [
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              "lessThanOrEqual": "11.6.0",
              "status": "affected",
              "version": "11.6.0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "11.5.3",
              "status": "affected",
              "version": "11.5.0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "11.4.4",
              "status": "affected",
              "version": "11.4.0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "10.11.14",
              "status": "affected",
              "version": "10.11.0",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "11.7.0"
            },
            {
              "status": "unaffected",
              "version": "11.6.1"
            },
            {
              "status": "unaffected",
              "version": "11.5.4"
            },
            {
              "status": "unaffected",
              "version": "11.4.5"
            },
            {
              "status": "unaffected",
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            }
          ]
        }
      ],
      "credits": [
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      ],
      "descriptions": [
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          "lang": "en",
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        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
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          "scenarios": [
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              "description": "CWE-789: Memory Allocation with Excessive Size Value",
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      "providerMetadata": {
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        "orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee",
        "shortName": "Mattermost"
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      "references": [
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          "tags": [
            "vendor-advisory"
          ],
          "url": "https://mattermost.com/security-updates"
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "value": "Update Mattermost to versions 11.7.0, 11.6.1, 11.5.4, 11.4.5, 10.11.15 or higher."
        }
      ],
      "source": {
        "advisory": "MMSA-2026-00647",
        "defect": [
          "https://mattermost.atlassian.net/browse/MM-68221"
        ],
        "discovery": "EXTERNAL"
      },
      "title": "Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server",
      "x_generator": {
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    }
  },
  "cveMetadata": {
    "assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee",
    "assignerShortName": "Mattermost",
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    "datePublished": "2026-05-22T10:22:01.030Z",
    "dateReserved": "2026-04-07T13:39:34.067Z",
    "dateUpdated": "2026-05-22T12:14:25.145Z",
    "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.