CVE-2026-6850
Received Received - Intake

Denial of Service in Mattermost via Malicious Markdown Payload

Publication date: 2026-07-13

Last updated on: 2026-07-13

Assigner: Mattermost, Inc.

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

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Meta Information

Published
2026-07-13
Last Modified
2026-07-13
Generated
2026-07-13
AI Q&A
2026-07-13
EPSS Evaluated
N/A
NVD
CVE-2026-6850
EUVD
EUVD-2026-43313

Affected Vendors & Products

Showing 3 associated CPEs
Vendor Product Version / Range
mattermost mattermost to 11.7.2 (inc)
mattermost mattermost to 11.6.4 (inc)
mattermost mattermost to 10.11.19 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-1333 The product uses a regular expression with an inefficient, possibly exponential worst-case computational complexity that consumes excessive CPU cycles.

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Executive Summary

This vulnerability affects certain versions of Mattermost (11.7.x <= 11.7.2, 11.6.x <= 11.6.4, and 10.11.x <= 10.11.19) where the application fails to properly validate the length and content of message attachment field values.

An authenticated attacker can exploit this by sending a post containing a specially crafted payload that triggers catastrophic backtracking in the client-side markdown parser.

This results in a denial of service (DoS) affecting all users in the channel.

Impact Analysis

The primary impact of this vulnerability is a denial of service (DoS) condition for all users in a channel.

An attacker who is authenticated can cause the client-side markdown parser to enter catastrophic backtracking, which can disrupt normal communication and availability within the affected Mattermost channels.

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