There was a specific vulnerability in VMWare a while back that
exploited the NAT process to break out of the VM and execute code in
the host system. You can find information about it in the CERT
advisory here: http://www.kb.cert.org/vuls/id/856689
Although this specific vulnerability has been patched, it illustrates
that the virtualization is not perfect. Sharing hardware resources
through software has both performance and security negative
implications. As you probably know for x86 systems, hardware
virtualization is a new concept, and only exists today in processors.
AMD has released specifications for I/O virtualization, but I don't
know of any chipsets have been released that support it.
Of course the mainframe folks get a kick out of all of this, as
they've had real hardware virtualization (LPARs) for a long time now.
- Chris Byrd
www.riosec.com
On 5/16/06, David M. Zendzian <dmz@dmzs.com> wrote:
All this talk about chroot makes me wonder about xen or vmware...anyone have
any thoughts/comments on breaking out of a virtual operating system?
-----Original Message-----
From: "Marco Ivaldi" <raptor@0xdeadbeef.info>
To: pen-test@securityfocus.com
Sent: 5/16/06 8:36 AM
Subject: Re: how an hacker can bypass a chrooted environement ?
Hey pen-test,
On Fri, 12 May 2006, Rob wrote:
> from man 2 chroot():
>
> -- Note that this call does not change the current working directory, so
> that '.' can be outside the tree rooted at '/'. In particular, the
> super-user can escape from a 'chroot jail' by doing 'mkdir foo; chroot
> foo; cd ..'. --
>
> Also, mknod() some device files like /dev/kmem or /dev/hda1, then use
> root priviledges to muck with kernel, or raw write data to disk.
Beside the already described techniques, here follows a quick summary of
some other rather old tricks to break out of the chroot jail:
1) Load a kernel module;) Capability needed: CAP_SYS_MODULE.
2) Speaking about the already mentioned mknod() technique (capability
needed: CAP_MKNOD), you could also use it to abuse ttys and virtual
file systems through the mount() syscall (capability needed:
CAP_SYS_ADMIN): procfs, devfs, devpts.
3) Inject code through ptrace() into a process outside the chroot jail,
provided you meet the required conditions to do so. This could work for
instance when the uid nobody is shared between several processes
(semi-common misconfiguration). Depending on the situation, this could
also be accomplished even with uid != 0. For further details, see also:
http://www.phrack.org/phrack/59/p59-0x0c.txt
4) Other uid != 0 tricks: (UNIX) sockets, shared memory segments and other
IPCs, exploiting local kernel vulnerabilities;), some other application
specific points.
5) Abuse sysctl() to set the modprobe binary path? Direct access to I/O
ports? Sniff network traffic? Impersonate a local administration
service (sshd)? Change netfilter rules? And so on... (you need
different capabilities for those).
I'm sure i left some possibilities out (use your fantasy), but i guess
this pretty much shows how you shouldn't blindly rely only on chroot to
secure your servers. YMMV.
Cheers,
--
Marco Ivaldi
Antifork Research, Inc. http://0xdeadbeef.info/
3B05 C9C5 A2DE C3D7 4233 0394 EF85 2008 DBFD B707
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