🛡️ CVE-2026-6850 — mattermost-server

🟡 CVSS 6.5 — Medium ✅ No Known Exploit CWE-1333 NVD
6.5
CVSS Score
0 Low4 Medium7 High9 Critical10

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

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

Weakness class

CVE-2026-6850 is classified as CWE-1333: Inefficient Regular Expression Complexity. A regular expression backtracks catastrophically on crafted input, consuming CPU out of proportion to input size.

Affected software

CVE-2026-6850 is recorded against 1 package.

  • mattermost-server (from 11.7.0 up to 11.7.3)

Timeline and source

Published on 13 July 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

mattermost.com

Details

Severity MEDIUM
CVSS Score 6.5
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CWE CWE-1333
Public Exploit ✅ No
Source NVD
Published 2026-07-13
Updated 2026-08-11
Modified 2026-07-13
Fix URL N/A

Affected Packages

Software From version Fixed in
mattermost-server 11.7.0 11.7.3

References

Similar Threats

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