Attachment Handling Flaw in Mattermost Web Application

CVE-2025-20621

Summary

Certain versions of Mattermost are susceptible to a vulnerability that arises from improper handling of posts with attachments. Specifically, the issue occurs when fields within these attachments cannot be cast to a String type. An attacker can exploit this flaw by sending specially crafted posts to a channel, which may result in the web application crashing and denying service to legitimate users. Organizations utilizing affected versions of Mattermost should review security patches to mitigate this risk.

References