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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