CVE-2026-2454 DoS in Calls plugin via malformed msgpack in websocket request.
A malicious user can crash the Mattermost server by sending malformed msgpack frames via websocket to the Calls plugin.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-2454?
CVE-2026-2454 is a medium-severity denial of service vulnerability in Mattermost Mattermost Server, published on 16 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Mattermost 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
Weakness: CWE-1287
Which versions are affected by CVE-2026-2454?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-2454?
No fix has been published for CVE-2026-2454 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-2454 being exploited?
There is no known exploitation of CVE-2026-2454 in the wild and no public exploit code.
Other vulnerabilities in Mattermost Mattermost Server
- CVE-2025-12419 Account takeover on OAuth/OpenID-enabled servers
- CVE-2025-12421 Account Takeover via Code Exchange Endpoint
- CVE-2025-4981 Path Traversal Leading to RCE by Any Authenticated Mattermost User
- CVE-2025-20051 Arbitrary file read via block duplication in Mattermost Boards
- CVE-2025-25279 Arbitrary file read in Mattermost Boards via import & export board archive
Sources
Also known as GHSA-3cx3-rw7f-7q37.