CVE-2026-2454: DoS in Calls plugin via malformed msgpack in websocket request.

Severity: high (CVSS 8.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-16 · updated 2026-06-17
Weakness: CWE-1287

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

Affected products

Mattermost: from 10.11.0 before 10.11.11; from 11.2.0 before 11.2.3; from 11.3.0 before 11.3.1 — fixed in 10.11.11, 11.2.3, 11.3.1

How to fix

Upgrade to a fixed version: Mattermost 10.11.11, 11.2.3, 11.3.1. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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