CVE-2026-25783

low-risk

Published 2026-03-16

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate User-Agent header tokens which allows an authenticated attacker to cause a request panic via a specially crafted User-Agent header. Mattermost Advisory ID: MMSA-2026-00586

Do I need to act?

0.07% chance of exploitation

EPSS score — low exploit probability

Not on CISA KEV list

No confirmed active exploitation reported to CISA

Patch status unknown

Check vendor advisories for fix availability and mitigation guidance

CVSS 4.3/10 Medium

NETWORK / LOW complexity

Affected Products (1)

Mattermost Server

Affected Vendors

Mattermost

References (1)

Vendor Advisory https://mattermost.com/security-updates

/ 100

low-risk

Severity 18/34 · Moderate

Exploitability 0/34 · Minimal

Exposure 5/34 · Minimal