Multiple Vulnerabilities in Mattermost Products

Multiple vulnerabilities have been discovered in Mattermost products as of May 2026. The vulnerabilities affect Mattermost Desktop App versions prior to 5.13.6, versions prior to 6.2, and Mattermost Server versions 10.11.x prior to 10.11.17, 11.5.x prior to 11.5.5, and 11.6.x prior to 11.6.2. These vulnerabilities allow an attacker to trigger unspecified security issues, posing a risk to organizations using these versions of Mattermost. The vendor has not provided specific details regarding the nature of these vulnerabilities. Defenders should prioritize patching.

Attack Chain

Due to the lack of specific vulnerability information, a generic attack chain is provided. This chain assumes a vulnerability allowing for remote code execution.

1. Attacker identifies a vulnerable Mattermost instance (Desktop App or Server) through reconnaissance.
2. Attacker crafts a malicious payload tailored to exploit the unspecified vulnerability.
3. Attacker delivers the payload to the Mattermost instance (e.g., via a crafted message, API call, or file upload).
4. The vulnerable Mattermost component processes the malicious payload, leading to code execution.
5. Attacker gains initial access to the system running the Mattermost instance.
6. Attacker performs privilege escalation to gain higher-level access.
7. Attacker moves laterally within the network, potentially targeting other systems or data.
8. Attacker achieves their objective, such as data exfiltration, system compromise, or service disruption.

Impact

Successful exploitation of these vulnerabilities could lead to a range of impacts, including unauthorized access to sensitive data, compromise of Mattermost servers and desktop applications, and potential lateral movement within the affected network. The lack of specifics from the vendor makes it difficult to assess the precise impact, but organizations should assume a potential for significant damage.

Recommendation

• Upgrade Mattermost Desktop App to version 5.13.6 or later, or version 6.2 or later, to remediate the vulnerabilities affecting the desktop application.
• Upgrade Mattermost Server to version 10.11.17 or later, 11.5.5 or later, or 11.6.2 or later, to remediate the vulnerabilities affecting the server.
• Monitor network traffic for suspicious activity originating from or directed towards Mattermost servers, as a compensating control.
• Enable verbose logging on Mattermost servers and desktop applications to facilitate incident response and investigation.