CVE-2026-6517

Name: CVE-2026-6517
Creator: NVD / NIST
Published: 2026-06-15T14:16:37.91+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.7/10EPSS 0.19%

Last modified Jun 17, 2026

CVE-2026-6517 is a high-severity vulnerability rated 7.7/10 on the CVSS scale. 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. EPSS estimates a 0.19% chance of exploitation in the next 30 days.

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

Metrics

CVSS 3.1

7.7/10

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

EPSS Probability

0.19%

8.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-522

Affected Software

Vendor	Product	Versions
Mattermost	Mattermost Desktop	<= 5.13.0
Mattermost	Mattermost Desktop	>= 6.1.0, <= 6.1.5

References

https://mattermost.com/security-updatesVendor Advisory

Timeline

Published: Jun 15, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-6517?

How severe is CVE-2026-6517?

CVE-2026-6517 has a CVSS score of 7.7/10 (HIGH severity). The EPSS model estimates a 0.19% probability of exploitation in the next 30 days.

How do I fix CVE-2026-6517?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-6517?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST