CVE-2026-8075: Posting a malicious markdown image crashes the Mattermost Desktop App

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-17 · updated 2026-10-15
Weakness: CWE-754

Description

Mattermost Desktop App versions <=6.2 5.5.13 6.0.2.0 fail to properly null check when checking for headers in the Mattermost Desktop App which allows any user to crash another channel members Desktop App via posting a malicious link with an embedded image that misses one of those headers. Mattermost Advisory ID: MMSA-2026-00668

Affected products

Mattermost Desktop: before 5.13.6; from 6.0.0 (excl.) through 6.0.2; from 6.2.0 before 6.2.1 — fixed in 5.13.6, 6.2.1

How to fix

Upgrade to a fixed version: Mattermost Desktop 5.13.6, 6.2.1. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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