CVE-2026-6517
Published: 15 June 2026
Summary
CVE-2026-6517 is a medium-severity Insufficiently Protected Credentials (CWE-522) vulnerability in Mattermost Mattermost Desktop. Its CVSS base score is 6.3 (Medium).
Operationally, ranked at the 8.4th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-36725
Vulnerability details
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…
more
other users credentials via embedding an image that routes to an external web server. Mattermost Advisory ID: MMSA-2026-00651
- CWE(s)
Related Threats
No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Training instructs users on protecting credentials from disclosure or unauthorized access.
Training records for security awareness and role-based training verify education on credential protection practices, tangibly reducing risks from mishandling or exposing credentials.
Protecting authenticator content from unauthorized disclosure and modification while requiring protective controls addresses insufficiently protected credentials.
Rules of behavior include credential protection and non-sharing requirements, reducing exposure of insufficiently protected credentials.
Terminating or revoking credentials stops use of insufficiently protected or lingering credentials post-termination.
Requiring confidentiality/integrity protection for stored credentials directly mitigates insufficiently protected credentials on disk or in configuration stores.
Credentials or keys delivered out-of-band are not exposed to interception or inadequate protection on the main transport.