Mattermost File Upload Vulnerability in Remote Cluster Sessions Allowing Arbitrary File Placement

A vulnerability exists in Mattermost versions 10.8.x through 10.8.3, 10.5.x through 10.5.8, 9.11.x through 9.11.17, 10.9.x through 10.9.2, and 10.10.x through 10.10.0. These versions fail to properly validate upload types in remote cluster upload sessions. This oversight enables system administrators to upload non-attachment file types via shared channels, potentially placing them in arbitrary directories on the filesystem.

Impact

Exploitation of this vulnerability could lead to unauthorized file uploads, allowing files to be placed in unintended locations on the server's filesystem.

Remediation

Users can upgrade to Mattermost versions 10.11.0, 10.5.10, 10.9.5, or 10.10.1 to address this vulnerability.