A remote attacker who gains administrative access can manipulate the gbadmin.cgi script using the ?action variable to change the "entry file" variable to arbitrary commands. This would allow the attacker to execute commands remotely with the privileges the web server runs under.
Unknown or Incomplete
Currently, there are no known upgrades or patches to correct this issue. It is possible to correct the flaw by disabling all access to the guestbook scripts until a patch or upgrade is made available.