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Mattermost WebSocket UTF-8 Validation Vulnerability Leading to Calls Plugin Crash

Vulnerability

A vulnerability exists in Mattermost versions 11.0.x prior to 11.0.4, 10.12.x prior to 10.12.2, and 10.11.x prior to 10.11.6. These versions do not properly validate the UTF-8 format of WebSocket request fields. This oversight allows an attacker to send malformed requests that can crash the Calls plugin.

Impact

Exploitation of this vulnerability leads to a crash of the Calls plugin.

Remediation

Users can upgrade to Mattermost versions 11.1.011.0.510.12.310.11.7 to address this vulnerability.

Added: Dec 17, 2025, 7:31 PM
Updated: Dec 17, 2025, 7:31 PM

Vulnerability Rating

Custom Algorithm
spread
3.1
impact
0.6
exploitability
5.2
remediation
7.7
relevance
1.4
threat
0.0
urgency
2.9
incentive
1.7

Our algorithm analyzes dozens of metrics to generate these 8 key vulnerability categories, which are then combined to calculate the overall risk score.