Open Source Ecosystems

virtunoid -- a guest -> host breakout for qemu-kvm Nelson Elhage [email protected] @nelhage http://blog.nelhage.com/

This is an exploit for CVE-2011-1751, a missing check in the qemu-kvm userspace driver for the KVM Linux Kernel-mode Virtual Machine. For more information, see the slides from my talk at BlackHat/DEFCON 2011: http://nelhage.com/talks/kvm-defcon-2011.pdf

RUNNING THE EXPLOIT

The exploit expects to be run as root inside a guest. For maximum reliability, the provided Makefile builds an initrd containing the exploit that can be used to run the exploit in as minimal an environment as possible. While I have seen the exploit work inside a fully booted Linux guest, there is a high chance of just crashing the host.

The provided linux-3.0.0-config Linux config file contains the config I used for my demo at DEFCON. The details of the config aren't too important, except that it needs to contain an appropriate driver for the virtual network card; I've just provided mine for convenience. I've also posted a suitable bzImage at https://nelhage.com/files/bzImage-kvm-demo.

To run the exploit, build an appopriate kernel or download mine, and run

kvm -kernel bzImage -initrd initrd.gz

virtunoid-config.h contains various addresses needed for the exploit. The provided version is targeted at Ubuntu's qemu-kvm_0.14.0+noroms-0ubuntu4_amd6, which can be downloaded from https://launchpad.net/ubuntu/+source/qemu-kvm/0.14.0+noroms-0ubuntu4/+build/2385343/+files/qemu-kvm_0.14.0%2Bnoroms-0ubuntu4_amd64.deb

For any other version, the addresses and some of the offsets in virtunoid-config.h will need to be tweaked.

KNOWN ISSUES

Most of these could be fixed, but I didn't feel particularly inclined for a proof-of-concept exploit. If you do feel like fixing one or more, let me know.

This exploit requires "-net user" with the default settings (or no -net options at all, which defaults to "-net nic -net user"). This requirement could be fixed, but this is a proof-of-concept.
This exploit only works on the specific Ubuntu qemu-kvm build it is built for. This exploit uses symbols that don't exist prior to qemu-kvm 0.13.51.
This exploit is still somewhat unreliable. I observe a failure rate of maybe 1 in 20 running it from an initrd on my test rig. There are a few different failure modes, the most common being SEGVing qemu-kvm instead of successful exploitation.
The guest locks up after the exploit.

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