CVE-2026-6850
Medium
Description
Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate the length and content of message attachment field values, which allows an authenticated attacker to cause a denial of service for all users in a channel via a post containing a specially crafted payload that triggers catastrophic backtracking in the client-side markdown parser.. Mattermost Advisory ID: MMSA-2026-00658
SeverityMedium
CVSS6.5
Exploit probability—
Product
Mattermost Server
PublishedJul 13, 2026
First seenJul 13, 2026
Weakness typeCWE-1333CWE-1333
How to fix
Update
- mattermost mattermost_server10.11.20, 11.6.5, 11.7.3 or later
Vendor advisories
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mattermost mattermost_server | 10.11.0 ≤ v < 10.11.20, 11.6.0 ≤ v < 11.6.5, 11.7.0 ≤ v < 11.7.3 | 10.11.20, 11.6.5, 11.7.3 |
Check your version
Choose the product and enter the version you run to see whether it falls in the affected range.
In the Intelligence 360 plan
Attack Surface Management
See the assets tied to your domains, the technologies they run and known vulnerabilities in one list.