Trustwave SpiderLabs Security Advisory TWSL2016-003:
Unsafe unlinking of files in Sophos Antivirus

Published: 03/09/2016
Version: 1.0

Vendor: Sophos (www.sophos.com)
Product: Sophos Anti-Virus
Version affected: prior to 9.2.10 for Mac OS X

Product description:
Anti-Virus for Mac OS X platform.

Finding 1: Unsafe unlinking of files
Credit: Martin Rakhmanov of Trustwave 

SophosAutoUpdate process on Mac OS X runs as root. It unsafely unlinks 
file /tmp/.com.sophos.sau.lock when Sophos Update is launched via GUI 
or via /usr/local/bin/SophosUpdate. As a result, any unprivileged local 
user can remove root-owned files, including configuration files.

Proof-of-concept:

As an unprivileged local user on Mac OS X, create symbolic link to some 
root-owned file via:

$ ln -s /etc/sudo_lecture /tmp/.com.sophos.sau.lock

Then run Sophos update (no permissions required):

$ /usr/local/bin/SophosUpdate

Observe that the /etc/sudo_lecture has zero length now.

Remediation Steps:
Upgrade to version 9.2.10 for Mac OS X. Sophos 9.3.x for Mac OS X is not 
affected.

Revision History:
01/25/2016 - Vulnerability disclosed to vendor
03/03/2016 - Vendor releases fix
03/09/2016 - Advisory published

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