dbcve.org
Mattermost ServerApplication · Mattermost

CVE-2026-2456

MEDIUM · 5.7 CVSS v3.1 Published 2026-03-16
Fix available
A fix is available. Upgrade to 10.11.11 / 11.2.3 or later.
See remediation →
61/100
Remediation priority · Elevated
Remotely reachable

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 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 Mattermost fails to limit the size of responses from integration action endpoints, which allows an authenticated attacker to cause server memory exhaustion and denial of service via a malicious integration server that returns an arbitrarily large response when a user clicks an interactive message button.. Mattermost Advisory ID: MMSA-2026-00571

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 enforce response size limits on integration action endpoints. An authenticated attacker can set up a malicious integration server that returns an arbitrarily large response when a user clicks an interactive message button, causing server memory exhaustion and denial of service.

MitigationUpdate Mattermost to the patched version as specified in MMSA-2026-00571. As an interim control, consider implementing response size limits at a reverse proxy or WAF in front of Mattermost.

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, < 10.11.11>= 11.2.0, < 11.2.3>= 11.3.0, < 11.3.1

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

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/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 'mmctl --version' or check the Mattermost System Console > About page for the exact version number
    Affected if Version is >= 10.11.0 and < 10.11.11, OR >= 11.2.0 and < 11.2.3, OR >= 11.3.0 and < 11.3.1
  2. Verify integration endpoints are accessible
    Check System Console > Integrations > Integration Management to see if custom integrations are enabled, or query the API endpoint /api/v4/integrations/actions
    Affected if Custom integrations or integration actions are enabled and accessible to authenticated users
  3. Identify configured integration plugins or webhooks
    Review System Console > Integrations > Webhooks and System Console > Plugins > Management for any installed integration plugins or outgoing webhooks that connect to external servers
    Affected if Any integration plugins or outgoing webhooks are configured to communicate with external integration servers
  4. Check for unusually high memory usage
    Monitor server memory consumption via 'top' or 'htop' commands, or check Mattermost logs for out-of-memory errors around integration action requests
    Affected if Memory exhaustion is occurring, particularly during interactive message button clicks

The environment is affected if Mattermost Server version falls within any of the listed vulnerable ranges AND integration action endpoints are accessible to authenticated users.

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 10.11.11 / 11.2.3 / 11.3.1 or later
Fixed in 10.11.1111.2.311.3.1
Interim mitigation

Update Mattermost to the patched version as specified in MMSA-2026-00571. As an interim control, consider implementing response size limits at a reverse proxy or WAF in front of Mattermost.

Recommended fix High confidence

Upgrade to 10.11.11 (for 10.11.x), 11.2.3 (for 11.2.x), or 11.3.1 (for 11.3.x) depending on your current branch

  1. 1. Identify your current Mattermost Server version using the system console or mmctl command
  2. 2. For version 10.11.x: upgrade to version 10.11.11 or later
  3. 3. For version 11.2.x: upgrade to version 11.2.3 or later
  4. 4. For version 11.3.x: upgrade to version 11.3.1 or later
  5. 5. Verify the upgrade was successful by checking the server version in the system console
  6. 6. Test interactive message buttons to ensure integration functionality still works correctly

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
  • Implementation3.0 h
  • Testing3.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-2456 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2026-2456 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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