linux security - Dec 1996 - FTP configurations?

This may be the wrong group, but here is my question anyway:

I havew a linux box that has ftp access for a few users, and shell access
allowed for no users.  The problem is, when I looked at my ftp permissions,
users are allowed full ftp access to the / bin drectory... here any way
that they can launch a shell session from the ftp session?  BTW, I''m
running wu-ftp 2.4

[mod: I would tag them as "guests" (/etc/ftpaccess?). This causes
wu-ftp to treat them about the same as anonymous ftp users. -- REW]

thanks,

gabe