The opieaccess file contains a list of networks that are considered trusted by the system as far as security against passive attacks is concerned. Users from networks so trusted will be able to log in using OPIE responses, but not be required to do so, while users from networks that are not trusted will always be required to use OPIE responses (the default behavior). This trust allows a site to have a more gentle migration to OPIE by allowing it to be non-mandatory for "inside" networks while allowing users to choose whether they with to use OPIE to protect their passwords or not.
The entire notion of trust implemented in the opieaccess file is a major security hole because it opens your system back up to the same passive attacks that the OPIE system is designed to protect you against. The opieaccess support in this version of OPIE exists solely because we believe that it is better to have it so that users who dont want their accounts broken into can use OPIE than to have them prevented from doing so by users who dont want to use OPIE. In any environment, it should be considered a transition tool and not a permanent fixture. When it is not being used as a transition tool, a version of OPIE that has been built without support for the opieaccess file should be built to prevent the possibility of an attacker using this file as a means to circumvent the OPIE software.
The opieaccess file consists of lines containing three fields separated by spaces (tabs are properly interpreted, but spaces should be used instead) as follows:
action "permit" or "deny" non-OPIE logins
addressAddress of the network to match
mask Mask of the network to match
Subnets can be controlled by using the appropriate address and mask. Individual hosts can be controlled by using the appropriate address and a mask of 255.255.255.255. If no rules are matched, the default is to deny non-OPIE logins.
ftpd(8) login(1), opie(4), opiekeys(5), opiepasswd(1), opieinfo(1),