Citrix Receiver/Receiver Desktop Lock 4.5 - Authentication Bypass

# thel3l

# Title: Citrix Receiver/Receiver Desktop Lock 4.5 Incorrect Access Control
# CVE: CVE-2016-9111
# Date of Discovery: October 27 2016
# Exploit Author: Rithwik Jayasimha
# Author Homepage/Contact: https://thel3l.me
# Vendor Name: Citrix
# Vendor Homepage: https://www.citrix.com/
# Software Link: Receiver - https://www.citrix.com/go/receiver.html
                 Receiver Desktop Lock - https://www.citrix.com/downloads/citrix-receiver/additional-client-software/receiver-desktop-lock-45.html
# Version: 10.6.3
# Tested on: Windows 8.1, macOS 10.12.1 Sierra
# Category: local
# Vulnerability type: Incorrect Access Control


# Description: Allows attacker with physical access to VDI to bypass authentication requirement. Citrix Receiver and/or Desktop Lock for Mac OSX and Windows suffer from a local incorrect access control.
To exploit this:
1. An attacker would first identify a VDI with a logged in user, which has been locked.
2. The attacker then proceeds to disconnect the system from the network temporarily (removing and reinserting the LAN cable is enough).
3. Citrix Receiver then proceeds to unlock the session and allows the attacker full access to the connected user's account without confirming the user's identity.

# Additional Notes, References and links:
    * This exploit is not 100% reliable - it may take a couple of tries to be able to accurately reproduce this behavior.
    * This attack has only been attempted with physical access - it may also be possible to remotely script a restart of a network adapter to cause the same behavior.