CVE-2026-6339

Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636

CVSS v3 4.3 MEDIUM

4.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required LOW

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact LOW

Scope UNCHANGED

References

Link	Resource
https://mattermost.com/security-updates	Vendor Advisory

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:mattermost:mattermost_server::::::::
	cpe:2.3:a:mattermost:mattermost_server::::::::

History

18 May 2026, 19:11

Type	Values Removed	Values Added
CPE		cpe:2.3:a:mattermost:mattermost_server::::::::
First Time		Mattermost mattermost Server Mattermost
References	~~() https://mattermost.com/security-updates -~~	() https://mattermost.com/security-updates - Vendor Advisory

18 May 2026, 09:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-05-18 09:16

Updated : 2026-05-18 19:11

NVD link : CVE-2026-6339

Mitre link : CVE-2026-6339

CVE.ORG link : CVE-2026-6339

JSON object : View

Products Affected

mattermost

mattermost_server

CWE

CWE-346

Origin Validation Error

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