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Re: [ GLSA 200408-16 ] glibc: Information leak with LD_DEBUG
From: Solar Designer <solar () openwall com>
Date: Sat, 21 Aug 2004 09:02:02 +0400

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


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