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Re: [ GLSA 200408-16 ] glibc: Information leak with LD_DEBUG
From: Jim Paris <jim () jtan com>
Date: Fri, 20 Aug 2004 03:24:53 -0400

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.

-jim


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