full-disclosure - Re: DLL hijacking on Linux

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Message-ID: <AANLkTimrYQ7vdT_weAYd8bocSSHWCyR5PJi+vrei1P5R@mail.gmail.com>
Date: Wed, 25 Aug 2010 13:23:52 -0400
From: Dan Rosenberg <dan.j.rosenberg@...il.com>
To: Tim Brown <tmb@...35.com>
Cc: security@...chdb.apache.org, full-disclosure@...ts.grok.org.uk
Subject: Re: DLL hijacking on Linux

Apache CouchDB (tested on Ubuntu 10.04) is vulnerable to exactly this
issue.  The script installed on my machine at /usr/bin/couchdb first
sets LD_LIBRARY_PATH with:

LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/lib/xulrunner-`xulrunner-1.9.2
--gre-version`/

At the time of invocation, the following environment is set up:

command="env \"LD_LIBRARY_PATH=/usr/lib:${LD_LIBRARY_PATH}\" \
...

So in the normal case where LD_LIBRARY_PATH is empty at the time of
invocation, the resulting path will be:

/usr/lib::/usr/lib/xulrunner-[version]/

The vulnerability to hijacking can be trivially verified by creating a
fake libc.so.6 in your current directory and running /usr/bin/couchdb.
 Fortunately, the init script changes directories before executing
couchdb, so exploitation is limited to cases where /usr/bin/couchdb is
invoked directly inside a hostile current directory.  Not a likely
exploitation scenario, but it still should probably be fixed.

-Dan

On Wed, Aug 25, 2010 at 5:58 AM, Tim Brown <tmb@...35.com> wrote:
> On Wednesday 25 August 2010 10:38:37 Mihai Donțu wrote:
>
>> man sudo(8):
>> "Note that the dynamic linker on most operating systems will remove
>> variables that can control dynamic linking from the environment of setuid
>> executables, including sudo. Depending on the operating system this may
>> include _RLD*, DYLD_*, LD_*, LDR_*, LIBPATH, SHLIB_PATH, and others. These
>> type of variables are removed from the environment before sudo even begins
>> execution and, as such, it is not possible for sudo to preserve them."
>
> Absolutely, but in the case I gave, the path is set /by the script/, not
> inherited from the original user.  The script sets the dangerous path, but
> since sudo hasn't changed the CWD it points at the directory the user running
> sudo was in.
>
> Tim
> --
> Tim Brown
> <mailto:tmb@...35.com>
>
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