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Mattermost User-Agent Header Validation Vulnerability Leading to Request Panic

Vulnerability

A vulnerability exists in Mattermost versions 11.3.x through 11.3.0, 11.2.x through 11.2.2, and 10.11.x through 10.11.10, where the application fails to properly validate tokens in the User-Agent header. This flaw allows an authenticated attacker to induce a request panic by sending a specially crafted User-Agent header.

Impact

Exploitation of this vulnerability causes a request panic, leading to a disruption in normal request processing.

Remediation

Users can upgrade to Mattermost versions 11.5.0, 11.4.0, or 11.3.1 to address this vulnerability.

Added: Mar 16, 2026, 2:20 PM
Updated: Mar 16, 2026, 2:20 PM

Vulnerability Rating

Custom Algorithm
spread
3.1
impact
2.5
exploitability
5.2
remediation
7.7
relevance
4.0
threat
0.0
urgency
2.9
incentive
0.0

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