# CVE-2026-4643: Mattermost Desktop App denial of service via window.close

Source: https://junglewise.ai/threats/cve-2026-4643-mattermost-desktop-app-denial-of-service-via-window-close  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-18. Updated: 2026-05-18  
License: CC BY 4.0 with a link back

CVE-2026-4643 · Severity: low · CVSS 3.5 · Published 2026-05-18

Mattermost is a collaboration platform used for team communication. A vulnerability in the Mattermost Desktop App allows a malicious server or plugin to force the application to close unexpectedly. This results in a denial-of-service for the user, disrupting their ability to communicate and collaborate until the application is restarted.

Technologies: [Mattermost Desktop App](https://junglewise.ai/threats/technologies/desktop-app). Vendors: [Mattermost](https://junglewise.ai/threats/vendors/mattermost).

## Quick answers

**Is CVE-2026-4643 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-4643 being exploited in the wild.

**How severe is CVE-2026-4643?** Low severity, with a CVSS score of 3.5, 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-2026-4643?** 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-2026-4643 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-4643?** 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 fails to properly sanitize or restrict server-rendered content from interacting with the underlying application view. Specifically, the application does not prevent the renderer context from invoking the window.close() method. An attacker controlling a malicious server or a malicious plugin can trigger this method to force the desktop client to close. This vulnerability is classified as an improper check for unusual or exceptional conditions (CWE-754). Exploitation requires a network-connected attacker with low privileges and some user interaction, resulting in a client-side denial of service.

## Affected products

- Mattermost Desktop App <=6.1, 6.0.1, 5.4.13.0

## Timeline

- 2026-05-18: disclosed: NVD publication date
- 2026-05-18: advisory: Mattermost Advisory MMSA-2026-00633 published

## References

- [https://mattermost.com/security-updates](https://mattermost.com/security-updates)

## Related threats

- [Mattermost Desktop App URL scheme validation bypass](https://junglewise.ai/threats/cve-2026-75588-mattermost-desktop-app-url-scheme-validation-bypass)
- [Mattermost Desktop App IPC validation bypass in leaveCall handler](https://junglewise.ai/threats/cve-2026-12284-mattermost-desktop-app-ipc-validation-bypass-in-leavecall-handler)
- [Mattermost Desktop App content restriction bypass](https://junglewise.ai/threats/cve-2026-75025-mattermost-desktop-app-content-restriction-bypass)
- [Mattermost Desktop App denial of service via malformed payload](https://junglewise.ai/threats/cve-2026-9602-mattermost-desktop-app-denial-of-service-via-malformed-payload)
- [Mattermost Desktop App denial of service via malicious image link](https://junglewise.ai/threats/cve-2026-8075-mattermost-desktop-app-denial-of-service-via-malicious-image-link)