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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-6850
StatePUBLISHED
AssignerMattermost
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-13 09:16:24 UTC
Updated2026-07-13 21:42:01 UTC
DescriptionMattermost 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

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from [email protected]

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

EPSS: 0.002400000 probability, percentile 0.150190000 (date 2026-07-14)

Problem Types: CWE-1333 | CWE-1333 CWE-1333: Inefficient Regular Expression Complexity

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
3.1CNACVSS6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Mattermost Mattermost Server All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mattermost Mattermost affected 11.7.0 11.7.2 semver Not specified
CNA Mattermost Mattermost affected 11.6.0 11.6.4 semver Not specified
CNA Mattermost Mattermost affected 10.11.0 10.11.19 semver Not specified
CNA Mattermost Mattermost unaffected 11.8.0 Not specified
CNA Mattermost Mattermost unaffected 11.7.3 Not specified
CNA Mattermost Mattermost unaffected 11.6.5 Not specified
CNA Mattermost Mattermost unaffected 10.11.20 Not specified

References

ReferenceSourceLinkTags
mattermost.com/security-updates [email protected] mattermost.com Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: idr (en)

Additional Advisory Data

Solutions

CNA: Update Mattermost to versions 11.8.0, 11.7.3, 11.6.5, 10.11.20 or higher.

© CVE.report 2026

Use of this information constitutes acceptance for use in an AS IS condition. There are NO warranties, implied or otherwise, with regard to this information or its use. Any use of this information is at the user's risk. It is the responsibility of user to evaluate the accuracy, completeness or usefulness of any information, opinion, advice or other content. EACH USER WILL BE SOLELY RESPONSIBLE FOR ANY consequences of his or her direct or indirect use of this web site. ALL WARRANTIES OF ANY KIND ARE EXPRESSLY DISCLAIMED. This site will NOT BE LIABLE FOR ANY DIRECT, INDIRECT or any other kind of loss.

CVE, CWE, and OVAL are registred trademarks of The MITRE Corporation and the authoritative source of CVE content is MITRE's CVE web site. This site includes MITRE data granted under the following license.

Free CVE JSON API cve.report/api

CVE.report and Source URL Uptime Status status.cve.report