CVE-2025-20621

Name of the Vulnerable Software and Affected Versions Mattermost versions 9.11.x through 9.11.5 Mattermost versions 10.0.x through 10.0.3 Mattermost versions 10.1.x through 10.1.3 Mattermost versions 10.2.x through 10.2.0

Description The issue arises from the improper handling of posts with attachments containing fields that cannot be cast to a String. This allows an attacker to cause the webapp to crash by creating and sending such a post to a channel.

Recommendations For Mattermost versions 9.11.x through 9.11.5, update to a version later than 9.11.5 to resolve the issue. For Mattermost versions 10.0.x through 10.0.3, update to a version later than 10.0.3 to resolve the issue. For Mattermost versions 10.1.x through 10.1.3, update to a version later than 10.1.3 to resolve the issue. For Mattermost versions 10.2.x through 10.2.0, update to a version later than 10.2.0 to resolve the issue. As a temporary workaround, consider restricting the creation and sending of posts with attachments to minimize the risk of exploitation.