CVE-2026-3471 PUBLISHED

Opening a window with {{javascript:alert()}} as URL causes crash in the Mattermost Desktop App

Assigner: Mattermost
Reserved: 03.03.2026 Published: 18.05.2026 Updated: 18.05.2026

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 the Mattermost Desktop App which allows a malicious server owner to repeated crash the application via calling {{window.open('javascript:alert()');}}. Mattermost Advisory ID: MMSA-2026-00618

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
CVSS Score: 6.5

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	None	Integrity Impact	None
User Interaction	Required	Availability Impact	High

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 0 to 6.0.1 (incl.) affected from 0 to 5.4.13 (incl.) Version 6.2.0 is unaffected Version 6.1.1.0 is unaffected Version 5.13.5.0 is unaffected

Solutions

Update Mattermost Desktop App to versions 6.2.0, 6.1.1.0, 5.13.5.0 or higher.

Credits

game0v3r finder

References

MMSA-2026-00618

Problem Types

CWE-939: Improper Authorization in Handler for Custom URL Scheme CWE