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Re: Glibc Local Root Exploit
From: Brian <bruns () MAGENET COM>
Date: Wed, 10 Jan 2001 15:57:19 -0500

In bash, simplest way to discourage idiots who are going to do this is
to put the following in /etc/bashrc or /etc/profile (if you use Bash, I
dont know about tcsh or the others):

readonly RESOLV_HOST_CONF=""

Its not fool-proof, and wont last long, and definately wont stop those
intent on doing damage, but hopefully this problem will get fixed

Brian Bruns
Valley Of The Mage Consulting
ICQ: 8077511

Charles Stevenson wrote:

Hi all,
  This has been bouncing around on vuln-dev and the debian-devel lists. It
effects glibc >= 2.1.9x and it would seem many if not all OSes using these
versions of glibc. Ben Collins writes, "This wasn't supposed to happen, and
the actual fix was a missing comma in the list of secure env vars that were
supposed to be cleared when a program starts up suid/sgid (including
RESOLV_HOST_CONF)." The exploit varies from system to system but in our
devel version of Yellow Dog Linux I was able to print the /etc/shadow file
as a normal user in the following manner:

export RESOLV_HOST_CONF=/etc/shadow
ssh whatever.host.com

  Other programs have the same effect depending on the defaults for the
system. I have tested this on Red Hat 7.0, Yellow Dog Linux 2.0
(prerelease), and Debian Woody. Others have reported similar results on
slackware and even "home brew[ed]" GNU/Linux.

Best Regards,
Charles Stevenson
Software Engineer

  Terra Soft Solutions, Inc

  Yellow Dog Linux

  Black Lab Linux

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