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CVE-2026-6850

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

Published: Jul 13, 2026Updated: Jul 13, 2026 Sources: CVE List NVDCWE-1333
6.5MEDIUM
NVD MITRE
EPSS Score
0.2%
Top 84.9%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available
Self-Check
OpenVAS

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

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:LPR:LUI:NS:UC:NI:NA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:LPrivileges Required
Low
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:NIntegrity
None
A:HAvailability
High
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Weaknesses

CWE-1333

Affected Products

Mattermost
commercial·US
MattermostOn-premWeb App
Communications / messaging-chat
mattermost serverOn-premWeb App
Communications / messaging-chat

Exploitability

Official Patch Available
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Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

1 technique
Impact
View detailed technique mapping

References

https://mattermost.com/security-updates
mattermost.com

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