CVE-2026-1628
📋 TL;DR
The Mattermost Desktop App vulnerability allows malicious Mattermost servers to expose preload script functionality to untrusted external sites when users click external links. This affects all users of Mattermost Desktop App versions 5.13.3 and earlier who interact with compromised or malicious Mattermost servers.
💻 Affected Systems
- Mattermost Desktop App
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Malicious server could execute arbitrary code on user's system through exposed preload scripts, potentially leading to full system compromise.
Likely Case
Malicious server could steal sensitive data from the Mattermost app or user's system through script injection.
If Mitigated
Limited data exposure from the Mattermost app context without system-level access.
🎯 Exploit Status
Exploitation requires user interaction (clicking external link) but the technical complexity is low once that occurs.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.14.0 or later
Vendor Advisory: https://mattermost.com/security-updates
Restart Required: Yes
Instructions:
1. Download Mattermost Desktop App version 5.14.0 or later from official sources. 2. Install the update. 3. Restart the application. 4. Verify version is updated.
🔧 Temporary Workarounds
Disable External Link Opening
allPrevent Mattermost from opening external links automatically
No CLI commands - Configure in Mattermost Desktop App settings
Use Web Browser Version
allUse Mattermost web interface instead of desktop app
🧯 If You Can't Patch
- Train users to avoid clicking external links from untrusted Mattermost servers
- Implement network controls to restrict access to potentially malicious external domains
🔍 How to Verify
Check if Vulnerable:
Check Mattermost Desktop App version in Help > About. If version is 5.13.3 or earlier, you are vulnerable.Check Version:
On Windows: Check Help > About. On macOS: Mattermost > About Mattermost. On Linux: Help > About.Verify Fix Applied:
Verify version is 5.14.0 or later in Help > About menu.📡 Detection & Monitoring
Log Indicators:
- Unusual external link navigation patterns
- Multiple failed navigation attempts to external domains
Network Indicators:
- Unexpected connections from Mattermost desktop app to external domains after clicking links
SIEM Query:
process.name:"Mattermost.exe" AND network.destination.domain:!mattermost.com AND network.destination.domain:!trusted-domains.com