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Mattermost ServerApplication · Mattermost

CVE-2026-6346

HIGH · 8.7 CVSS v3.1 Published 2026-05-18
Fix available
A fix is available. Upgrade to 10.11.14 / 11.4.4 or later.
See remediation →
93/100
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 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to sanitize sensitive configuration fields before including them in support packet generation, which allows a Mattermost System Admin or any party with access to a support packet to obtain sensitive credentials in plaintext via downloading a support packet from the System Console.. Mattermost Advisory ID: MMSA-2026-00607

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 sanitize sensitive configuration fields (such as API keys, database passwords, and other credentials) before including them in support packet generation. This allows any System Admin or party with access to a downloaded support packet from the System Console to obtain these sensitive credentials in plaintext, resulting in information disclosure.

MitigationUpgrade Mattermost to version 11.5.2, 10.11.14, or 11.4.4 or later. Until patched, restrict access to support packet downloads to only trusted administrators and treat support packets as highly sensitive files containing secrets.

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, < 10.11.14>= 11.4.0, < 11.4.4>= 11.5.0, < 11.5.2

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
Changed
Confidentiality
High
Integrity
High
Availability
None

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

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 installed Mattermost Server version
    Use the Mattermost system console or run 'mmctl version' or check the /opt/mattermost/version file to determine the exact version number installed
    Affected if The installed version falls within any of these ranges: 10.11.0 to 10.11.13, 11.4.0 to 11.4.3, or 11.5.0 to 11.5.1
  2. Verify access to System Console support packet feature
    Check admin audit logs for events related to support packet generation or download, typically found in System Console > Audit Logs
    Affected if Any support packets were generated or downloaded from the System Console
  3. Identify sensitive credentials in Mattermost configuration
    Review Mattermost configuration files (config.json) and environment variables for API keys, database passwords, integration tokens, or other secrets that may have been included in support packets
    Affected if The system contains sensitive credentials in configuration that could have been included in a support packet
  4. Locate any existing support packet files
    Search server filesystem for recently created support packet files (typically .zip files generated from System Console > Support > Support Packet)
    Affected if Any support packet files exist on the server or were downloaded

A user is affected if their Mattermost Server version is within the affected ranges AND any support packet containing sensitive configuration data was generated or downloaded.

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 10.11.14 / 11.4.4 / 11.5.2 or later
Fixed in 10.11.1411.4.411.5.2
Interim mitigation

Upgrade Mattermost to version 11.5.2, 10.11.14, or 11.4.4 or later. Until patched, restrict access to support packet downloads to only trusted administrators and treat support packets as highly sensitive files containing secrets.

Recommended fix High confidence

Mattermost Server 10.11.14, 11.4.4, or 11.5.2 (or later)

  1. 1. Plan a maintenance window and backup your Mattermost Server data and database
  2. 2. Upgrade Mattermost Server to version 10.11.14 (if on 10.11.x), 11.4.4 (if on 11.4.x), or 11.5.2 (if on 11.5.x) - or any later version
  3. 3. After upgrade, verify the version in System Console > About Mattermost
  4. 4. Test that support packet generation now properly redacts or masks sensitive configuration fields before download

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
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,640
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,224.

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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-2026-6346 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