CVE-2026-6517

🔶 medium

Summary

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 Score

6.3

Medium

EPSS Score

0.2

Exploit Probability

Published Date

2026-06-15

First Seen: 2026-06-16

📊 Relative Risk Intelligence

This CVE is Lower Risk - more severe than 39.3% of all 328,009 vulnerabilities in our database.

#199,264

Below average severity

Severity Percentile

🎯 CISA SSVC Assessment Updated: Jun 15, 2026

🔍 Exploitation Status

None

No known exploits

⚙️ Automatable

Requires human interaction

💥 Technical Impact

Partial

Limited system impact

🏆 Discovered By

falke

SSVC data provided by CISA

Last Modified 2026-06-16

Source NVD 🔗

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

CWE IDs (Weakness Types)

CWE-522

📦 Affected Products 2

Vendor	Product	Status	Affected Versions
mattermost	mattermost_desktop	Affected	< 5.13.0
mattermost	mattermost_desktop	Affected	> 6.1.0 < 6.1.5

🔗 References 1

https://mattermost.com/security-updates

Vendor Advisory

🔗 Related CVEs 6

CVE ID	Severity	CVSS	EPSS	Summary	Published
CVE-2026-8683	🔶 medium	6.5	0.2	Mattermost Desktop App versions <=6.1 5.5.13.0 fail to account for attempting to open extremely long URLs in the Matterm...	2026-06-15
CVE-2026-3471	🔶 medium	6.5	0.0	Mattermost Desktop App versions <=6.1 6.0.1 5.4.13.0 fail to prevent an invalid URL from loading in a pop-up window in t...	2026-05-18
CVE-2026-4643	ℹ️ low	3.5	0.0	Mattermost Desktop App versions <=6.1 6.0.1 5.4.13.0 fail to prevent server-rendered content from closing an underlying ...	2026-05-18
CVE-2026-1628	🔶 medium	4.6	0.0	Mattermost Desktop App versions <=5.13.3 fail to attach listeners restricting navigation to external sites within the Ma...	2026-03-02
CVE-2026-1046	⚠️ high	7.6	0.0	Mattermost Desktop App versions <=6.0 6.2.0 5.2.13.0 fail to validate help links which allows a malicious Mattermost ser...	2026-02-16
CVE-2025-13321	ℹ️ low	3.3	0.0	Mattermost Desktop App versions <6.0.0 fail to sanitize sensitive information from Mattermost logs and clear data on ser...	2025-12-17

These CVEs affect the same products