Vulnerability Note VU#551972
Synology Cloud Station sync client for OS X allows regular users to claim ownership of system files
Original Release date: 26 May 2015 | Last revised: 27 May 2015

Overview
The Synology Cloud Station sync client for OS X contains a setuid root executable that allows regular users to claim ownership of system files.

Description
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.

Impact
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.

Solution
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.

Vendor Information (Learn More)

VendorStatusDate NotifiedDate UpdatedSynologyAffected06 Apr 201526 May 2015If you are a vendor and your product is affected, let
us know.

CVSS Metrics (Learn More)

Group
Score
Vector

Base
6.8
AV:L/AC:L/Au:S/C:C/I:C/A:C

Temporal
5.3
E:POC/RL:OF/RC:C

Environmental
1.3
CDP:ND/TD:L/CR:ND/IR:ND/AR:ND

References

None

Credit

Thanks to Jeremy Kemp for reporting this vulnerability to us.
This document was written by Garret Wassermann.

Other Information

CVE IDs:
CVE-2015-2851

Date Public:
26 May 2015

Date First Published:
26 May 2015

Date Last Updated:
27 May 2015

Document Revision:
49

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