==============================ADVISORY===============================
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
==============================ADVISORY===============================
 
Description
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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. 
 
Analysis
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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
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Citrix XenServer 6.0
Citrix XenServer 5.6
Citrix XenServer 5.5
Citrix XenServer 5.0
 
Vendor Response
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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
 
Credits
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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