Re: [ GLSA 200408-16 ] glibc: Information leak with LD_DEBUG

[Solar Designer <solar () openwall com>]

On Fri, Aug 20, 2004 at 03:24:53AM -0400, Jim Paris wrote:
> > Silvio Cesare discovered a potential information leak in glibc. It
> > allows LD_DEBUG on SUID binaries where it should not be allowed. This
> > has various security implications, which may be used to gain
> > confidentional information.
>
> It's worse than that.  You can essentially single-step through the
> library calls of a binary by turning on verbose debugging through
> LD_DEBUG and then carefully controlling stdout so that the program
> blocks while writing the debugging output.  I've used this to exploit
> race conditions in setuid binaries that would otherwise be nearly
> impossible to trigger.
>
> Gentoo's method of adding LD_DEBUG to UNSECURE_ENVVARS will prevent
> this.

FWIW, this has been dealt with in Openwall GNU/*/Linux (Owl) before our
project was first announced to the public 3+ years ago.  ALT Linux is
another (or the other?) distribution vendor which also dealt with this
roughly 3 years ago.

Our patch sets and replacements for the various packages are available
for consideration and possible re-use by other distributions.  The
patches are easy to get without having to download the entire system -
as a small tarball (only 1.5 MB gzipped) available on our FTP mirrors
or from our public anoncvs and CVSweb servers:

        http://www.openwall.com/Owl/DOWNLOAD.shtml

-- 
Alexander Peslyak <solar at openwall.com>
GPG key ID: B35D3598  fp: 6429 0D7E F130 C13E C929  6447 73C3 A290 B35D 3598
http://www.openwall.com - bringing security into open computing environments