CVE-2026-6517

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

Published: Jun 15, 2026Updated: Jun 16, 2026 Sources: CVE List NVDCWE-522

6.3MEDIUM

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

No summary for this CVE yet.

CVSS Vector Breakdown

Exploitability

AV:NAttack Vector

Network

AC:HAttack Complexity

High

PR:LPrivileges Required

Low

UI:NUser Interaction

None

Scope

S:CScope

Changed

Impact

C:HConfidentiality

High

I:NIntegrity

None

A:NAvailability

None

Open in CVSS calculator →

Weaknesses

CWE-522

Affected Products

Mattermost

commercial·US

mattermost desktopOn-premDesktop App

Communications / messaging-chat

MattermostOn-premWeb App

Communications / messaging-chat

Exploitability

Official Patch Available

Is your org exposed to CVE-2026-6517?Request an assessment to establish which checks are appropriate for your systems. Check my exposure

Attack Graph

Products CVE Techniques Tactics

Click technique nodes for MITRE ATT&CK details · drag to pan · Ctrl/⌘ + scroll to zoom, or go fullscreen.

MITRE ATT&CK

2 techniques

Credential Access

View detailed technique mapping

References

https://mattermost.com/security-updates

mattermost.com

Unlock Complete Vulnerability Intelligence

Get the full picture for CVE-2026-6517 and every CVE in our database. Create a free account — no credit card required.

Create Free Account

Plain-language analysis

Impact assessment and exploitation scenario in plain English

Attack graph visualization

Interactive attack path and kill chain mapping

Exploit details & PoC links

ExploitDB, Metasploit, GitHub PoCs with direct links

Nuclei scanner templates

Ready-to-use vulnerability scanner templates

Full remediation guide

Patch instructions, workarounds, and compliance impact

Interactive AI chat

Ask questions about this vulnerability in natural language

Related vulnerabilities

Semantically similar CVEs and attack patterns

REST API & MCP access

Integrate vulnerability data into your workflows