Quick answers
- Is CVE-2026-3471 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-3471 being exploited in the wild.
- How severe is CVE-2026-3471?
- Medium severity, with a CVSS score of 6.5, published 18 May 2026.
- Which products and versions are affected?
- Mattermost Desktop App <=6.1, 6.0.1, 5.4.13.0.
- Is there a fix for CVE-2026-3471?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-3471 attacked?
- It is attacked over the network, in a network appliance.
- Am I affected by CVE-2026-3471?
- Check whether you run Mattermost Desktop App at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
The Mattermost Desktop App contains a vulnerability classified under CWE-939 (Improper Authorization in Handler for Custom URL Scheme). The application fails to properly validate or restrict URLs when opening new windows via the window.open() method. A malicious server owner can exploit this by calling window.open('javascript:alert()'), which causes the desktop client to crash. This is a remote attack requiring user interaction (connecting to the malicious server) and results in a high impact on application availability.
Affected products
- Mattermost Desktop App <=6.1, 6.0.1, 5.4.13.0
Timeline
- 2026-05-18: disclosed
- 2026-05-18: advisory