CVE-2026-6517

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

Published Jun 15, 2026 CVSS 3.1 · 6.3 Medium EPSS < 1% KEV · Not listed
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

Remediation

Vendor Solution

Update Mattermost Desktop App to versions 6.2.0, 5.13.6.0 or higher.

Tracking

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Advisories

No advisories available
References
History
Type Values Removed Values Added
First Time appeared Mattermost mattermost Desktop
CPEs cpe:2.3:a:mattermost:mattermost_desktop:*:*:*:*:*:*:*:*
cpe:2.3:a:mattermost:mattermost_desktop:*:-:*:*:*:*:*:*
Vendors & Products Mattermost mattermost Desktop
Type Values Removed Values Added
First Time appeared Mattermost
Mattermost mattermost
Vendors & Products Mattermost
Mattermost mattermost
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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
Title Mattermost Desktop App fails to restrict the allow list of domains which NTLM credentials are passed
Weaknesses CWE-522
References
Metrics cvssV3_1

{'score': 6.3, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
Mattermost
Published
Updated
Jun 15, 2026, 4:00 PM
Reserved
Apr 17, 2026, 2:25 PM
Status
Analyzed
Published
Jun 15, 2026, 2:16 PM
Modified
Jun 17, 2026, 11:00 AM