CVE-2026-3471 — Mattermost Desktop App versions <=6.1 6.0.1 5.4.13.0 fail
CVE-2026-3471 — 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 Adv
What This Means For You
- If your environment is affected by CWE-939, review your exposure and prioritize patching based on your environment. Monitor vendor advisories for CVE-2026-3471 updates and patches.
Related ATT&CK Techniques
🛡️ Detection Rules
2 rules · 6 SIEM formats2 detection rules auto-generated for this incident, mapped to MITRE ATT&CK. Sigma YAML is free — export to any SIEM format via the Intel Bot.
Mattermost Desktop App Crash via JavaScript URI - CVE-2026-3471
title: Mattermost Desktop App Crash via JavaScript URI - CVE-2026-3471
id: scw-2026-05-18-ai-1
status: experimental
level: critical
description: |
Detects the specific crash condition in Mattermost Desktop App (versions <=6.1, 6.0.1, 5.4.13.0) where a malicious server owner can trigger an application crash by forcing the app to load a 'javascript:alert()' URI in a pop-up window. This rule specifically looks for the Mattermost executable being launched with this malicious JavaScript URI in its command line.
author: SCW Feed Engine (AI-generated)
date: 2026-05-18
references:
- https://shimiscyberworld.com/posts/nvd-CVE-2026-3471/
tags:
- attack.initial_access
- attack.t1190
logsource:
category: process_creation
detection:
selection:
Image|endswith:
- 'Mattermost.exe'
CommandLine|contains:
- 'javascript:alert()'
condition: selection
falsepositives:
- Legitimate administrative activity
Source: Shimi's Cyber World · License & reuse
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-3471 | vulnerability | CVE-2026-3471 |
| CWE-939 | weakness | CWE-939 |
Written by SCW Vulnerability Desk
Source & Attribution
| Source Platform | NVD |
| Channel | National Vulnerability Database |
| Published | May 18, 2026 at 12:16 UTC |
This content was curated and summarized by Shimi's Cyber World for informational purposes. It is not copied or republished in full. All intellectual property rights remain with the original author and source.
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