Medium 6.3Published Jun 15, 2026

CVE-2026-6517Mattermost Desktop App fails to restrict the allow list of domains which NTLM credentials are passed

Updated under an hour ago (Oct 26, 2026, 8:30 PM ET)

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No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

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

CVSS: 6.3 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N
Weakness (CWE): CWE-522
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: Mattermost
NVD analysis: Analyzed
Record last updated: Jun 15, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Mattermost Mattermost mattermost:mattermost (from the name)	through 5.5.13; 6.2.0 not affected; 5.13.6.0 not affected	CNA record
mattermost mattermost_desktop mattermost:mattermost_desktop	through 5.13.0; from 6.1.0 through 6.1.5	NVD

References

References

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

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.