I've been told that the exec in exec password actually stands for "Executable".. However, myself and those I know typically refer to it as "Executive". The exec password on a Cisco 67x DSL Modem/Router is the password that allows you access to the CBOS. Some information to note:

1) You cannot use telnet to configure the 67x if you do not have an executive password set.

2) You can use the Cisco Commander software to set/change the executive password, thus enabling you to telnet into the router.

3) If you don't have an executive password set, and you don't have the commander software, or commander doesn't work for you, you can still terminal in (with HyperTerminal on a Windows box, or Zterm on a Mac) and set one from in there. In order to do this you do have to have the managment cable provided with the modem. If you are able to terminal in, and are able to get to a "CBOS#" prompt, I recommend you type "set password exec -password-" to enable telneting into the router (its alot easier than going through a terminal).

If none of those conditions are met -- you're screwed, because you cannot enter the router to configure it. Your options at this point are to call up your DSL provider and try to get them to RMA you a new management cable. Which still may not help if you have a Macintosh. If you have a mac with serial ports (other than USB), you will have to purchase an adapter for your management cable in order to terminal in. These adapters are about $80 dollars.