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Context IS Advisory - Citrix XenServer Hypervisor Privilege Escalation
From: Context IS - Disclosure <disclosure () contextis co uk>
Date: Tue, 30 Oct 2012 09:13:21 +0000

Systems Affected:      Citrix XenServer 5.0 through 6.0.2
Severity:                    High
Category:                  Privilege Escalation
Author:                     Context Information Security
Reported to vendor:  24th May 2012
Advisory Issued:       30th October 2012
Reference:                CVE-2012-4606
The XenServer remote VNC terminal emulator contains a vulnerability which would allow a user of a guest VM to get code 
executing in the hypervisor leading to elevation of privilege on the server on which the guest VM was being hosted. 
Citrix XenServer is distributed with a VT100 terminal emulator which is exposed via the VNC protocol to allow a remote 
user to administer their hosted para-virtualised machine.  The application does not correctly handle certain escape 
sequences which can lead to an unprivileged guest VM being able to gain code execution in the fully privileged Dom0 
allowing the entire hosting server to be controlled. 
It should be noted that the vulnerable code was also used in the QEMU-KVM terminal that can be used by emulated virtual 
machines; this is under a different CVE, CVE-2012-3515.
Technologies Affected
Citrix XenServer 6.0
Citrix XenServer 5.6
Citrix XenServer 5.5
Citrix XenServer 5.0
Vendor Response
Vendor issued a security hot fix of the 5th September 2012. See http://support.citrix.com/article/CTX134708 for support 
information and download locations for different versions of XenServer. 
Disclosure Timeline
24th May 2012 – Vendor notified
5th September 2012 – Vendor issues fix
James Forshaw of Context Information Security
About Context Information Security
Context Information Security is an independent security consultancy specialising in both technical security and 
information assurance services.
The company was founded in 1998. Its client base has grown steadily over the years, thanks in large part to personal 
recommendations from existing clients who value us as business partners. We believe our success is based on the value 
our clients place on our product-agnostic, holistic approach; the way we work closely with them to develop a tailored 
service; and to the independence, integrity and technical skills of our consultants.
The company’s client base now includes some of the most prestigious blue chip companies in the world, as well as 
government organisations. 
The best security experts need to bring a broad portfolio of skills to the job, so Context has always sought to recruit 
staff with extensive business experience as well as technical expertise. Our aim is to provide effective and practical 
solutions, advice and support: when we report back to clients we always communicate our findings and recommendations in 
plain terms at a business level as well as in the form of an in-depth technical report.
Web:        www.contextis.com
Email:      disclosure () contextis co uk
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