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Mattermost ServerApplication · Mattermost

CVE-2026-6062

MEDIUM · 6.4 CVSS v3.1 Published 2026-06-22
Fix available
A fix is available. Upgrade to 10.11.18 / 11.5.6 or later.
See remediation →
70/100
Remediation priority · Elevated
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 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 Fail to validate channel ownership of an existing subscription before applying edits which allows an authenticated attacker to hijack subscriptions from channels they have no access to via a crafted PUT request to the subscription edit endpoint.. Mattermost Advisory ID: MMSA-2026-00650

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

This is an Insecure Direct Object Reference (IDOR) vulnerability in Mattermost's subscription edit endpoint. The application fails to validate channel ownership before applying edits to subscriptions, allowing authenticated attackers to craft PUT requests that hijack subscriptions from channels they have no access to.

MitigationUpgrade to Mattermost versions later than 11.7.0, 11.6.2, 11.5.5, and 10.11.17 as specified in MMSA-2026-00650.

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, < 10.11.18>= 11.5.0, < 11.5.6>= 11.6.0, < 11.6.3>= 11.7.0, < 11.7.1

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

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/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
    Run 'mattermost version' or inspect the /opt/mattermost/version file, or check the system information in the Mattermost System Console under About > Mattermost
    Affected if The installed version falls within any of these ranges: 10.11.0 through 10.11.17, 11.5.0 through 11.5.5, 11.6.0 through 11.6.2, or 11.7.0
  2. Verify subscription edit API exposure
    Review API endpoint documentation or server logs for access to /api/v4/subscriptions endpoints, specifically PUT requests that modify subscription configurations
    Affected if The subscription edit endpoint is exposed and accessible to authenticated users
  3. Inspect server logs for suspicious subscription modifications
    Search Mattermost server logs (typically in /var/log/mattermost or via the logging API) for PUT requests to subscription endpoints where the requesting user lacks channel membership or channel access
    Affected if Logs show subscription modification attempts from users on channels they do not have access to
  4. Audit subscription ownership in database
    Query the database (PostgreSQL or MySQL) for subscriptions where the UserId does not match a member of the ChannelId, or compare subscription records against channel membership tables
    Affected if Database contains subscription records linking users to channels they are not members of

You are affected if your Mattermost Server version is 10.11.0-10.11.17, 11.5.0-11.5.5, 11.6.0-11.6.2, or 11.7.0 AND your logs or database show unauthorized subscription modifications from users accessing channels they do not belong to.

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 10.11.18 / 11.5.6 / 11.6.3 or later
Fixed in 10.11.1811.5.611.6.3
Interim mitigation

Upgrade to Mattermost versions later than 11.7.0, 11.6.2, 11.5.5, and 10.11.17 as specified in MMSA-2026-00650.

Recommended fix High confidence

10.11.18 (for 10.11.x), 11.5.6 (for 11.5.x), 11.6.3 (for 11.6.x), or 11.7.1 (for 11.7.x)

  1. 1. Identify current Mattermost Server version by checking the system console or running 'mattermost version' command
  2. 2. Determine which version branch you are currently on (10.11.x, 11.5.x, 11.6.x, or 11.7.x)
  3. 3. For 10.11.x branch: upgrade to version 10.11.18 or later
  4. 4. For 11.5.x branch: upgrade to version 11.5.6 or later
  5. 5. For 11.6.x branch: upgrade to version 11.6.3 or later
  6. 6. For 11.7.x branch: upgrade to version 11.7.1 or later
  7. 7. Follow Mattermost upgrade documentation to apply the update
  8. 8. Verify the upgrade was successful and the server is functioning normally
Caveat Standard Mattermost minor/patch upgrade risks apply - review release notes for any configuration or feature changes

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
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA3.0 h
20.0 hours of engineering $3,480
Get the upgrade done

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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-2026-6062 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