dbcve.org
Mattermost ServerApplication · Mattermost

CVE-2026-10085

MEDIUM · 5.4 CVSS v3.1 Published 2026-07-13
Fix available
A fix is available. Upgrade to 10.11.20 / 11.6.5 or later.
See remediation →
60/100
Remediation priority · Elevated
Remotely reachable Zero-click 5 weeks old

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 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to restrict the group_constrained channel flag to public and private channels that support group synchronization, which allows an ordinary group or direct message member to remove all participants from the conversation via the channel patch API.. Mattermost Advisory ID: MMSA-2026-00688

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 · moderate confidence

Mattermost fails to restrict the group_constrained channel flag to only public and private channels that support group synchronization. This allows an ordinary member of a group or direct message conversation to exploit the channel patch API and remove all participants from the conversation, bypassing proper authorization controls.

MitigationUpgrade Mattermost to versions 11.7.3+, 11.6.5+, or 10.11.20+ to receive the security patch. Additionally, review audit logs for unauthorized participant removals and implement least-privilege access controls on channel management permissions until the upgrade is complete.

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, < 10.11.20>= 11.6.0, < 11.6.5>= 11.7.0, < 11.7.3

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
None
Integrity
Low
Availability
Low

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

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 > About > Mattermost or query the server API endpoint /api/v4/system/info to retrieve the version string
    Affected if The installed version is >=10.11.0 and <10.11.20, OR >=11.6.0 and <11.6.5, OR >=11.7.0 and <11.7.3
  2. Identify group_constrained channels in use
    Query the Mattermost API for channels with the group_constrained flag set to true, or navigate to Channel Settings > Group Sync to enumerate channels with group synchronization enabled
    Affected if Group-constrained channels exist in the environment, allowing group members to interact with the channel patch API
  3. Review audit logs for unauthorized participant removals
    Access the Mattermost audit logs (System Console > Audit Logs) or query the audit API for events involving the removal of channel participants, filtering for non-admin user actions on the /channels/{id}/members endpoint
    Affected if Audit logs show participant removal events performed by ordinary channel members rather than only by admins or users with proper channel management permissions

A user is affected if they are running a Mattermost Server version within the affected ranges AND have group-constrained or group-synchronized channels in use, where ordinary members could exploit the channel patch API to remove participants without authorization.

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 10.11.20 / 11.6.5 / 11.7.3 or later
Fixed in 10.11.2011.6.511.7.3
Interim mitigation

Upgrade Mattermost to versions 11.7.3+, 11.6.5+, or 10.11.20+ to receive the security patch. Additionally, review audit logs for unauthorized participant removals and implement least-privilege access controls on channel management permissions until the upgrade is complete.

Recommended fix High confidence

10.11.20 (for 10.11.x); 11.6.5 (for 11.6.x); 11.7.3 (for 11.7.x)

  1. 1. Identify the currently running Mattermost Server version using the system console or mmctl command
  2. 2. For Mattermost 10.11.x: Upgrade to version 10.11.20 or later
  3. 3. For Mattermost 11.6.x: Upgrade to version 11.6.5 or later
  4. 4. For Mattermost 11.7.x: Upgrade to version 11.7.3 or later
  5. 5. After upgrade, verify the patch API no longer allows unauthorized participant removal from group_constrained channels

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

Fix this in Mattermost Server Scoped from the published advisory
  • Consultation3.0 h
  • Implementation12.0 h
  • Testing6.0 h
  • Review / QA3.0 h
24.0 hours of engineering $4,200
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,720.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-10085 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2026-10085 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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