Software Engineering Institute

CWE-276: Incorrect Default Permissions - CVE-2015-2851

The Synology Cloud Station sync client for OS X contains an executable named client_chown that allows users to change the ownership of files. However, by default, it is installed as a setuid root executable. This allows any user the ability to change ownership of arbitrary system files, which may be leveraged to gain root privileges and fully compromise the host.

Versions of Synology Cloud Station sync client from 1.1-2291 up to 3.1-3320 are vulnerable.

A local standard OS X user may gain ownership over arbitrary system files, which may be leveraged to gain root privileges and fully compromise the host.

Update the client

Synology has released version 3.2-3475, which addresses this issue. According to Synology, "We have removed client_chown in the latest build (3.2-3475) as precaution, even though the impact is concluded to be very low. The client_chown tool was originally designed to ease the upgrade process of the Cloud Station client, and was included starting from build 2291. To achieve this purpose, client_chown was able to change the ownership of certain system files that belong to Cloud Station client."

Affected users are encouraged to update to version 3.2-3475 or later as soon as possible.