CVE-2026-6850 | Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.1… | CVSS 6.5 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

Metadata

CVE ID: CVE-2026-6850
State: PUBLISHED
Assigner: Mattermost
Reserved: 2026-04-22 10:05 UTC
Published: 2026-07-13 08:13 UTC
Last updated: 2026-07-13 13:56 UTC
Primary CWE: CWE-1333
CWE-1333: Inefficient Regular Expression Complexity
Vendor / Product: Mattermost / Mattermost
Sources: cve.org · NVD

Severity & Metrics

6.5 MEDIUM CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

SSVC — CISA Coordinator

Exploitation: none
Automatable: no
Tech. Impact: partial

Affected products (1)

Vendor	Product	Platform	Versions
Mattermost	Mattermost	—	11.7.0 ≤ 11.7.2, 11.6.0 ≤ 11.6.4, 10.11.0 ≤ 10.11.19, 11.8.0 …

Weakness (CWE)

CWE	Source	Description
CWE-1333	cna	CWE-1333: Inefficient Regular Expression Complexity

CVSS scores (1)

Score	Severity	Version	Source	Vector
6.5	MEDIUM	3.1	cna	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

References (1)

MMSA-2026-00658 https://mattermost.com/security-updates