It indicates an attempt to execute potentially malicious command via bslist.cgi program.
Due to insufficient input validation, a remote attacker can execute arbitrary commands on a victim system via specially-crafted email address.
Any unprotected Brian Stanback bslist.cgi 1.0 is vulnerable to the attack.
Attackers can run arbitrary shell commands with the privilege level of the web server.
Upgrade the script to the latest non-vulnerable version.