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Mattermost ServerApplication · Mattermost

CVE-2026-7387

HIGH · 8.8 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 →
94/100
Remediation priority · Urgent
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 Mattermost fails to require role-management authorization when setting the scheme_admin flag on group syncable link and patch endpoints, which allows a user with group-link permissions to escalate themselves and group members to team or channel admin via crafted API requests.. Mattermost Advisory ID: MMSA-2026-00665

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 role-management authorization on group syncable link and patch endpoints when the scheme_admin flag is set. Users with group-link permissions can craft API requests to escalate themselves or group members to team or channel admin privileges, achieving privilege escalation through improper authorization on group synchronization endpoints.

MitigationUpdate Mattermost to the patched version as specified in MMSA-2026-00665. Until patched, restrict group-link permission assignments and monitor API activity for suspicious privilege escalation attempts.

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
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/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. Check Mattermost Server version
    Access the Mattermost System Console and navigate to About > Mattermost, or use the command line: `mattermost version` or check the /opt/mattermost/version file. Compare the installed version number against the affected ranges: 10.11.0 through 10.11.16, 11.5.0 through 11.5.4, and 11.6.0 through 11.6.1.
    Affected if The installed version falls within any of these ranges: >=10.11.0 and <10.11.17, >=11.5.0 and <11.5.5, or >=11.6.0 and <11.6.2.
  2. Verify if group synchronization is enabled
    Navigate to Mattermost System Console > User Management > Groups, or check the system configuration for group synchronization settings. Verify whether groups are synced with AD/LDAP or other identity providers.
    Affected if Group synchronization with external identity providers is enabled and active.
  3. Identify users with group-link permissions
    Review user roles and permissions in System Console > User Management > Users. Check which users have been granted group-link permissions or are members of groups that have link permissions to teams or channels.
    Affected if There exist users with group-link permissions who could potentially craft API requests to group syncable endpoints.
  4. Audit recent group syncable API activity
    Review Mattermost server logs for API calls to group synchronization endpoints (typically under /api/v4/groups endpoints). Look for requests that include scheme_admin flag modifications or role changes on group-linked teams or channels.
    Affected if API activity shows requests to group syncable endpoints with scheme_admin parameter modifications, indicating potential exploitation attempts.

You are affected if your Mattermost Server version is within the vulnerable ranges AND group synchronization is enabled, allowing users with group-link permissions to potentially escalate privileges through API endpoints.

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

Update Mattermost to the patched version as specified in MMSA-2026-00665. Until patched, restrict group-link permission assignments and monitor API activity for suspicious privilege escalation attempts.

Recommended fix High confidence

Mattermost Server 10.11.17 (for 10.11.x), 11.5.5 (for 11.5.x), or 11.6.2 (for 11.6.x)

  1. 1. Backup your Mattermost Server database and configuration files before upgrading.
  2. 2. Identify your current Mattermost Server version by navigating to System Console > About > Mattermost.
  3. 3. For Mattermost 10.11.x: Upgrade to version 10.11.17 or later.
  4. 4. For Mattermost 11.5.x: Upgrade to version 11.5.5 or later.
  5. 5. For Mattermost 11.6.x: Upgrade to version 11.6.2 or later.
  6. 6. Use your package manager or the official Mattermost upgrade guide to apply the update (e.g., apt-get update && apt-get install mattermost-server for Debian/Ubuntu, or yum install mattermost-server for RHEL/CentOS).
  7. 7. After upgrade, verify the Mattermost service is running and users can log in.
  8. 8. Confirm the version has been updated in System Console > About > Mattermost.
Caveat Review Mattermost release notes for your target version to check for any breaking changes or deprecations

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
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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-2026-7387 in production — separate from our analysis above.

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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