full-disclosure - Re: DLL hijacking on Linux

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Date: Wed, 25 Aug 2010 13:55:22 -0400
From: Dan Rosenberg <dan.j.rosenberg@...il.com>
To: Tim Brown <tmb@...35.com>
Cc: security@...ian.org, security@...chdb.apache.org,
	full-disclosure@...ts.grok.org.uk, security <security@...ntu.com>
Subject: Re: DLL hijacking on Linux

...And it looks like I jumped the gun on blaming upstream.  The
vulnerability was introduced by Debian patch
"mozjs1.9_ldlibpath.patch" on 3/24/2009.

-Dan

On Wed, Aug 25, 2010 at 1:23 PM, Dan Rosenberg
<dan.j.rosenberg@...il.com> wrote:
> 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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>

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