CVE-2026-6850

MEDIUM

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

Title source: cna
STIX 2.1

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

References (1)

Core 1
Core References
Vendor Advisory vendor-advisory
MMSA-2026-00658
https://mattermost.com/security-updates

Scores

CVSS v3 6.5
EPSS 0.0024
EPSS Percentile 14.3%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CISA SSVC

Vulnrichment
Exploitation none
Automatable no
Technical Impact partial

Details

CWE
CWE-1333
Status published
Products (8)
Mattermost/Mattermost 10.11.0 - 10.11.19
Mattermost/Mattermost 10.11.20
Mattermost/Mattermost 11.6.0 - 11.6.4
Mattermost/Mattermost 11.6.5
Mattermost/Mattermost 11.7.0 - 11.7.2
Mattermost/Mattermost 11.7.3
Mattermost/Mattermost 11.8.0
mattermost/mattermost_server 10.11.0 - 10.11.20
Published Jul 13, 2026
Tracked Since Jul 13, 2026