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virtunoid -- a guest -> host breakout for qemu-kvm Nelson Elhage <firstname.lastname@example.org> @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 <http://dl.dropbox.com/u/2595898/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. LEGALESE -------- Copyright (c) Nelson Elhage. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. 3. The name of the author may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.