CVE-2013-6795 Vulnerability in the Rackspace Windows Agent and Updater

[andrew () cloudpassage com]

A vulnerability in the Rackspace Windows Agent and Updater was discovered that allows for modified Agent binaries to be 
remotely uploaded (without authentication) to Rackspace Cloud Server guest instances. Modified Agent binaries are 
processed as an update for the Agent and arbitrary code can then be executed after the service is restarted. 
CloudPassage disclosed the vulnerability to Rackspace and CVE-2013-6795 was issued by MITRE Corporation.

The Windows Agent and Updater is used by Windows Cloud Server instances on OpenStack Nova to handle boot configurations 
for Windows guests running on the Xen hypervisor. The agent was created by Rackspace for their Windows instances and 
both the Agent and Updater services run under the LocalSystem account.

Previous versions of the Updater (before 1.2.6.0) allowed for unsigned agent updates utilizing a specially crafted .NET 
remote call to TCP port 1984. The Update service takes a single .NET serializable object with a URL and an MD5 
checksum. Once the sequence is triggered, a ZIP file is downloaded, verified using the checksum, and extracted into the 
program folder of the Agent service before the service is restarted. No authentication is performed by the .NET 
remoting service, making it possible to deploy a modified Agent update that overwrites the running Agent service 
binary. A proof of concept tool was developed to trigger the sequence with an arbitrary download URL using the original 
.NET libraries from a target.

Full details here: http://blog.cloudpassage.com/2013/11/18/cve-2013-6795-vulnerability-rackspace-windows-agent-updater/

CloudPassage responsibly disclosed the finding to Rackspace and, as of version 1.2.6.0, the Updater has been changed to 
use IPC with XenStore and no longer listens on port 1984. Rackspace recommends that users running the Windows agent 
less than version 1.2.6.1 update to the latest version, available on GitHub at 
https://github.com/rackerlabs/openstack-guest-agents-windows-xenserver.