Re: how an hacker can bypass a chrooted environement ?

[Marco Ivaldi <raptor () 0xdeadbeef info>]

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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