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MattermostApplication

CVE-2026-24661

MEDIUM · 6.5 CVSS v3.1 Published 2026-04-09
Fix available
A fix is available. Upgrade to 2.3.2.0 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 Plugins versions <=2.1.3.0 fail to limit the request body size on the {{/changes}} webhook endpoint which allows an authenticated attacker to cause memory exhaustion and denial of service via sending an oversized JSON payload. Mattermost Advisory ID: MMSA-2026-00611

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 Plugins versions <=2.1.3.0 lack request body size limits on the /changes webhook endpoint, allowing authenticated attackers to send oversized JSON payloads that exhaust server memory and cause denial of service.

MitigationUpgrade Mattermost Plugins to a version >2.1.3.0 that implements proper request body size limits, or implement input validation and request size restrictions at the application or proxy layer.

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
MattermostApplication
Affected:< 2.3.2.0

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. Identify Mattermost installation and version
    Run 'mattermost version' or check the system package manager, or query the Mattermost API at /api/v4/system/config with an admin token to retrieve the Version field
    Affected if The installed Mattermost version is lower than 2.3.2.0
  2. Determine if plugins are enabled
    Check the Mattermost config file (typically in /opt/mattermost/config/config.json) for the 'PluginSettings' section, or query the API endpoint /api/v4/plugins
    Affected if Plugin functionality is enabled and plugins are installed
  3. Locate the plugin version in use
    Query the Mattermost Marketplace API at /api/v1/plugins/marketplace or inspect the plugins directory (typically /opt/mattermost/plugins) for installed plugin manifests and version metadata
    Affected if Any plugin version is 2.1.3.0 or lower, or if the plugin providing /changes webhook functionality is present at any version <=2.1.3.0
  4. Verify /changes webhook endpoint exposure
    Review the plugin configuration in the Mattermost UI under System Console > Plugins, or examine the plugin's manifest.json and webapp routes to confirm the /changes endpoint is active and accessible
    Affected if The /changes webhook endpoint is exposed and accepts external requests

Your environment is affected if Mattermost version is below 2.3.2.0 and a plugin with the /changes webhook endpoint at version 2.1.3.0 or lower is installed and enabled.

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 2.3.2.0 or later
Fixed in 2.3.2.0
Interim mitigation

Upgrade Mattermost Plugins to a version >2.1.3.0 that implements proper request body size limits, or implement input validation and request size restrictions at the application or proxy layer.

Recommended fix Moderate confidence

Mattermost server >= 2.3.2.0

  1. 1. Identify the current Mattermost server version by navigating to System Console > About or checking the /api/v4/config/client endpoint
  2. 2. Download the latest Mattermost server version >= 2.3.2.0 from the official Mattermost download page (mattermost.com)
  3. 3. Create a complete backup of the Mattermost database and file storage directory before upgrading
  4. 4. Stop the Mattermost server service
  5. 5. Install the Mattermost server version 2.3.2.0 or later using the appropriate installation method for your deployment (e.g., tar.gz, Docker, or package manager)
  6. 6. Start the Mattermost server service and verify the upgrade was successful
  7. 7. Verify the plugin API endpoint now properly enforces request body size limits by testing with normal-sized payloads
Caveat Review Mattermost release notes for 2.3.x for any breaking changes between your current version and the target version, particularly regarding plugin API compatibility

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

Fix this in Mattermost Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing8.0 h
  • Review / QA4.0 h
24.0 hours of engineering $4,160
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-2026-24661 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