CVE-2026-2454
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 · uneditedMattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to handle incorrectly reported array lengths which allows malicious user to cause OOM errors and crash the server via sending corrupted msgpack frames within websocket messages to calls plugin. Mattermost Advisory ID: MMSA-2025-00537
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 · moderate confidenceThe Mattermost calls plugin fails to validate array length fields in msgpack deserialization, allowing malicious users to send crafted websocket messages with falsified length values that trigger excessive memory allocation (OOM) and crash the server.
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>= 10.11.0, < 10.11.11>= 11.2.0, < 11.2.3>= 11.3.0, < 11.3.1CVSS 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
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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 checksWork through these to decide whether this CVE applies to you.
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Identify Mattermost Server versionRun 'mmctl version' or check the system console under About > Mattermost, or inspect the Docker/container logs on startupAffected if The installed version falls within >= 10.11.0 and < 10.11.11, OR >= 11.2.0 and < 11.2.3, OR >= 11.3.0 and < 11.3.1
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Confirm calls plugin is enabledNavigate to System Console > Plugins > Management, or run 'mmctl plugin list' to see active pluginsAffected if The calls plugin (com.mattermost.calls) is installed and enabled
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Check websocket exposure to calls pluginVerify that the calls plugin websocket endpoint (/plugins/com.mattermost.calls/api/v4/calls) is accessible and not blocked by network policiesAffected if Websocket connections to the calls plugin are allowed from authenticated users
A user is affected if they run a vulnerable Mattermost Server version (10.11.0-10.11.10, 11.2.0-11.2.2, or 11.3.0) with the calls plugin enabled and accessible via websocket.
Generated from the published advisory. Verify against your own configuration.
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 · scoped10.11.1111.2.311.3.1
Upgrade Mattermost to versions newer than 11.3.0, 11.2.2, and 10.11.10 to obtain the patched calls plugin with proper msgpack array length validation.
Upgrade to 10.11.11 (for 10.11.x branch), 11.2.3 (for 11.2.x branch), or 11.3.1 (for 11.3.x branch)
- Backup your Mattermost Server data and configuration before upgrading
- Identify your current Mattermost version (Help > About in the Mattermost UI or via the API)
- For version 10.11.x: Upgrade to version 10.11.11 or later
- For version 11.2.x: Upgrade to version 11.2.3 or later
- For version 11.3.x: Upgrade to version 11.3.1 or later
- After upgrade, restart the Mattermost server and verify the calls plugin is functioning properly
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-2454 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-2454 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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
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