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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

PUBLISHED Reserved 2026-04-17 | Published 2026-06-15 | Updated 2026-06-15 | Assigner Mattermost




MEDIUM: 6.3CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N

Problem types

CWE-522: Insufficiently Protected Credentials

Product status

Default status
unaffected

Any version
affected

6.2.0
unaffected

5.13.6.0
unaffected

Credits

falke finder

References

mattermost.com/security-updates (MMSA-2026-00651) vendor-advisory

cve.org (CVE-2026-6517)

nvd.nist.gov (CVE-2026-6517)

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