CVE-2026-6850 Details
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
A denial-of-service vulnerability has been identified in Mattermost versions 11.7.x prior to 11.7.2, 11.6.x prior to 11.6.4, and 10.11.x prior to 10.11.19. The issue arises because these versions do not properly validate the length and content of message attachment field values. This flaw allows an authenticated attacker to disrupt service for all users in a channel by posting a message with a specially crafted payload that exploits catastrophic backtracking in the client-side markdown parser.
Users can upgrade to Mattermost versions 11.8.0, 11.7.5, or 11.6.10 to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Jul 13, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://mattermost.com/security-updates | [email protected] | Vendor Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-1333 | Inefficient Regular Expression Complexity | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| mattermost mattermost server | >= 10.11.0, < 10.11.20 >= 11.6.0, < 11.6.5 >= 11.7.0, < 11.7.3 |
CPE
Remediation
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Change History
3 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 13, 2026 | Initial Analysis | [email protected] |
| Jul 13, 2026 | CVE Modified | CISA-ADP |
| Jul 13, 2026 | New CVE Received | [email protected] |