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Mattermost ServerApplication · Mattermost

CVE-2026-6347

HIGH · 7.6 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 →
82/100
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 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to sanitize sensitive configuration fields in the Mattermost Calls plugin which allows an attacker with access to a support packet to obtain TURN server credentials via the plaintext values present in the exported plugin configuration.. Mattermost Advisory ID: MMSA-2026-00605

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 in the Calls plugin, exposing TURN server credentials in plaintext within exported support packets. An attacker with access to these support packets can retrieve the credentials.

MitigationUpdate Mattermost to a patched version beyond 11.5.1, 10.11.13, or 11.4.3. Rotate TURN server credentials as a precautionary measure since they may have been exposed in existing support packets.

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
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:N/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 'mmctl version' or check the system console About page to identify the installed Mattermost Server version number.
    Affected if The installed version falls within >= 10.11.0 and < 10.11.14, OR >= 11.4.0 and < 11.4.4, OR >= 11.5.0 and < 11.5.2.
  2. Verify Calls plugin is enabled
    Navigate to System Console > Plugins > Plugin Management, or run 'mmctl plugin list' to confirm the 'com.mattermost.calls' plugin is installed and enabled.
    Affected if The Calls plugin is installed and enabled on the server.
  3. Confirm TURN server credentials are configured
    Navigate to System Console > Plugins > Calls > TURN servers, or inspect the configuration file (config.json) for 'TurnServerURIs' and 'TurnServerCredentials' fields under the Calls plugin settings.
    Affected if TURN server credentials are configured in the Calls plugin settings.
  4. Review exported support packets for exposed credentials
    Locate any previously exported support packets (通常在 System Console > Support > Export or logs 目录中), search within them for plaintext TURN credentials (look for 'turn:' or 'turns:' URLs containing usernames and passwords).
    Affected if Exported support packets contain plaintext TURN server credentials.

A user is affected if they run a vulnerable Mattermost Server version with the Calls plugin enabled AND have TURN server credentials configured, especially if support packets have been exported.

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

Update Mattermost to a patched version beyond 11.5.1, 10.11.13, or 11.4.3. Rotate TURN server credentials as a precautionary measure since they may have been exposed in existing support packets.

Recommended fix High confidence

Upgrade to 10.11.14 (for 10.11.x), 11.4.4 (for 11.4.x), or 11.5.2 (for 11.5.x)

  1. 1. Identify current Mattermost Server version by accessing System Console > About or running `mattermost version`
  2. 2. For versions 10.11.x (<10.11.14): Upgrade to version 10.11.14 or later
  3. 3. For versions 11.4.x (<11.4.4): Upgrade to version 11.4.4 or later
  4. 4. For versions 11.5.x (<11.5.2): Upgrade to version 11.5.2 or later
  5. 5. After upgrade, verify the Mattermost Calls plugin configuration in System Console > Plugins > Calls
  6. 6. Ensure TURN server credentials in configuration are not exported in plaintext in any support packets
Caveat Standard minor version upgrades; review release notes for any configuration changes

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

Fix this in Mattermost Server Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,088.

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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-2026-6347 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