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Mattermost ServerApplication · Mattermost

CVE-2026-6739

HIGH · 7.2 CVSS v3.1 Published 2026-06-12
Fix available
A fix is available. Upgrade to 10.11.17 / 11.5.5 or later.
See remediation →
78/100
Remediation priority · High
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to require system-level permission when patching protected default system roles, which allows authenticated users with delegated user-management permissions to escalate privileges by altering built-in role permissions via the role patch API.. Mattermost Advisory ID: MMSA-2026-00656

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Mattermost fails to enforce system-level permission checks when patching protected default system roles through the role patch API. Authenticated users with delegated user-management permissions can exploit this to escalate privileges by modifying built-in role permissions, bypassing the required system-level authorization.

MitigationUpgrade to patched versions of Mattermost (11.6.2+, 11.5.5+, 10.11.16+, 10.11.17+) or restrict delegated user-management permissions until patches can be applied.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Mattermost ServerApplication
Affected:>= 10.11.0, < 10.11.17>= 11.5.0, < 11.5.5>= 11.6.0, < 11.6.2

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
High
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Mattermost Server version
    Query the /api/v4/system/about endpoint or check the Mattermost logs for the ServerVersion field
    Affected if The version falls within any of these ranges: 10.11.0-10.11.16, 11.5.0-11.5.4, or 11.6.0-11.6.1
  2. Audit user accounts with delegated user-management permissions
    Query the /api/v4/users endpoint and examine the roles field for users assigned permissions that include user_management roles (such as system_user_manager, system_admin, or custom roles with user management capabilities)
    Affected if Any user account possesses delegated user-management permissions and the server version is vulnerable
  3. Review current state of protected default system roles
    Query the /api/v4/roles endpoint to retrieve all system roles and compare their current permission sets against known defaults, particularly checking for unexpected modifications to roles named 'system_admin', 'system_user_manager', or other built-in roles
    Affected if Any protected default system role contains permissions that were not assigned by default or shows recent modification timestamps you did not authorize
  4. Check API access logs for role patch operations
    Search server and API logs for POST or PATCH requests to /api/v4/roles/{role_id}/patch or similar endpoints that modify role permissions, filtering for requests made by non-system-admin users
    Affected if There are logged role patch API calls from users who do not hold full system administrator privileges

You are affected if your Mattermost Server version is 10.11.0-10.11.16, 11.5.0-11.5.4, or 11.6.0-11.6.1 AND you have users with delegated user-management permissions who could access the role patch API.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 10.11.17 / 11.5.5 / 11.6.2 or later
Fixed in 10.11.1711.5.511.6.2
Interim mitigation

Upgrade to patched versions of Mattermost (11.6.2+, 11.5.5+, 10.11.16+, 10.11.17+) or restrict delegated user-management permissions until patches can be applied.

Recommended fix High confidence

Upgrade to Mattermost Server 10.11.17 (or later 10.11.x), 11.5.5 (or later 11.5.x), or 11.6.2 (or later 11.6.x) based on your current branch

  1. 1. Identify the currently running Mattermost Server version using the system console or CLI
  2. 2. Based on your current major version (10.11.x, 11.5.x, or 11.6.x), plan upgrade to the minimum fixed version: 10.11.17, 11.5.5, or 11.6.2 respectively
  3. 3. Review Mattermost upgrade documentation and ensure backup of database and configuration files
  4. 4. Schedule maintenance window as upgrades may require brief service interruption
  5. 5. Perform upgrade following Mattermost standard upgrade procedures for your deployment type (helm chart, docker, or manual)
  6. 6. After upgrade, verify the system is operational and test role-based access controls
  7. 7. Confirm the role patch API now correctly requires system-level permissions for protected default system roles
Caveat Standard Mattermost upgrade considerations apply - review release notes for any migration requirements or configuration changes between minor versions

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Mattermost Server Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,176.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-6739 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data