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CVE-2026-6517

Mattermost Desktop App fails to restrict the allow list of domains which NTLM credentials are passed

Published: Jun 15, 2026Updated: Jun 16, 2026 Sources: CVE List NVDCWE-522
6.3MEDIUM
NVD MITRE
EPSS Score
0.2%
Top 91.6%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available
Self-Check
OpenVAS

Description

Mattermost Desktop App versions <=6.1 5.5.13.0 fail to restrict the allow list of domains to which NTLM credentials were forwarded to in the Mattermost Desktop App which allows any user on a server without the image proxy enabled to intercept other users credentials via embedding an image that routes to an external web server. Mattermost Advisory ID: MMSA-2026-00651

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:HPR:LUI:NS:CC:HI:NA:N
Exploitability
AV:NAttack Vector
Network
AC:HAttack Complexity
High
PR:LPrivileges Required
Low
UI:NUser Interaction
None
Scope
S:CScope
Changed
Impact
C:HConfidentiality
High
I:NIntegrity
None
A:NAvailability
None
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Weaknesses

CWE-522

Affected Products

Mattermost
commercial·US
mattermost desktopOn-premDesktop App
Communications / messaging-chat
MattermostOn-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

2 techniques
Credential Access
View detailed technique mapping

References

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

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