CVE-2026-6850 — Crafted message attachment causes client-side denial of service via markdown parser regex backtracking in Mattermost

CVE-2026-6850

Crafted message attachment causes client-side denial of service via markdown parser regex backtracking in Mattermost PUBLISHED

Description (CNA)

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

Affected (CNA)

Vendor / product	Versions
Mattermost / Mattermost	affected 11.7.0 through 11.7.2; affected 11.6.0 through 11.6.4; affected 10.11.0 through 10.11.19; unaffected 11.8.0; unaffected 11.7.3; unaffected 11.6.5; unaffected 10.11.20

CWE

CWE-1333

References

https://mattermost.com/security-updates

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.