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Mattermost ServerApplication · Mattermost

CVE-2025-20088

MEDIUM · 6.5 CVSS v3.1 Published 2025-01-15
Fix available
A fix is available. Upgrade to 9.11.6 / 10.0.4 or later.
See remediation →
71/100
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 10.2.x <= 10.2.0, 9.11.x <= 9.11.5, 10.0.x <= 10.0.3, 10.1.x <= 10.1.3 fail to properly validate post props which allows a malicious authenticated user to cause a crash via a malicious post.

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 properly validate post properties (post props), allowing an authenticated malicious user to send specially crafted posts with malformed props that cause the server to crash (denial of service). The vulnerability exists across multiple versions in the 9.x and 10.x branches due to missing or insufficient input validation on post metadata.

MitigationUpgrade Mattermost to versions 10.2.1, 10.1.4, 10.0.4, or 9.11.6 or later which contain proper post props validation. As a compensating control, limit user permissions or monitor for abnormal post creation patterns.

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:>= 9.11.0, < 9.11.6>= 10.0.0, < 10.0.4>= 10.1.0, < 10.1.4= 10.2.0

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
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/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 installed Mattermost Server version
    Run 'mattermost version' from the server command line, or access the System Console > About page in the web UI, or check the /api/v4/system/about endpoint
    Affected if The version is 9.11.0 through 9.11.5, 10.0.0 through 10.0.3, 10.1.0 through 10.1.3, or exactly 10.2.0. These versions are within the affected ranges.
  2. Confirm Mattermost is configured to accept posts from authenticated users
    Verify that user authentication is enabled and users have permissions to create posts. Check System Console > Users and Teams > Teams or verify authentication method in System Console > Authentication
    Affected if The server allows authenticated users to post. The vulnerability requires an authenticated user to send malformed post props, so if posting is restricted to system admins only, the attack surface is reduced but not eliminated.
  3. Check if the server has any API request logging or audit logs
    Review Mattermost logs in the /var/log/mattermost directory or via the System Console > Logs. Look for patterns of post creation API calls (/api/v4/posts) that may indicate exploitation attempts
    Affected if Logs show abnormal post creation patterns, high volumes of post API requests, or server crash events correlating with specific post submissions from regular users.
  4. Verify server accessibility to non-admin users
    Review user roles and permissions in System Console > User Management > Roles. Determine if regular users or guest accounts can create posts in any channel
    Affected if Regular authenticated users (non-admin) have post creation permissions, which is required for this vulnerability to be exploitable.

If the Mattermost Server version falls within any of the affected ranges (9.11.0-9.11.5, 10.0.0-10.0.3, 10.1.0-10.1.3, or 10.2.0) AND the server allows authenticated users to create posts, the environment is affected by this CVE.

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 9.11.6 / 10.0.4 / 10.1.4 or later
Fixed in 9.11.610.0.410.1.4
Interim mitigation

Upgrade Mattermost to versions 10.2.1, 10.1.4, 10.0.4, or 9.11.6 or later which contain proper post props validation. As a compensating control, limit user permissions or monitor for abnormal post creation patterns.

Recommended fix High confidence

9.11.6, 10.0.4, 10.1.4, or 10.2.1 (depending on your current major version)

  1. Identify the currently installed Mattermost Server version using the system console or mmctl command
  2. Backup the Mattermost database and config file before upgrading
  3. For Mattermost 9.11.x: upgrade to version 9.11.6 or later
  4. For Mattermost 10.0.x: upgrade to version 10.0.4 or later
  5. For Mattermost 10.1.x: upgrade to version 10.1.4 or later
  6. For Mattermost 10.2.0: upgrade to version 10.2.1 or later when available
  7. Follow standard Mattermost upgrade documentation for your deployment method (docker, helm, or manual)
  8. Verify the upgrade was successful by checking the server version in the system console

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
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,800
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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-2025-20088 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