Additional Security in BNU UUCP

Creating additional passwd file entries to grant individual access to separate calling systems • Restricting local file access by remote system, or requiring a call−back for certain system logins • Controlling the remotely executed commands • Controlling the forwarding of files from and for other systems • Assigning appropriate file access modes and ownership to protect the UUCP files with sensitive data from outside users • We will pass quickly through most of these issues. On most systems, the etcpasswd file includes the uucp entry which specifies needed administrative data UUCP user and group ID, and indirectly the ownership of all UUCP directories and files and working environment upon login working directory and, instead of the usual shell, the spawned initial program uucico. On some systems two separate user entries exist for the same purpose. Here is an extracted uucp user entry: cat etcpasswd | grep uucp uucp:x:5:3::usrspooluucppublic:usrlibuucpuucico As can be seen from the entry, the UUCP working directory is the spool directory usrspooluucppublic, and the started program is uucico. The UUCP password entry is the regular part of any user authentication; however, the account is closed by default and must be activated. Often multiple UUCP accounts are provided, as in this example from HP−UX 10.20: cat etcpasswd | grep uucp uucp::5:3::varspooluucppublic:usrlbinuucpuucico nuucp::11:9::varspooluucppublic:usrlbinuucpuucico Multiple UUCP accounts give more flexibility; it is possible to provide different access to the system for different remote systems, based on the corresponding UUCP login name. However, in this example, both accounts are closed pay attention to the asterisk in the password field — it means UUCP is not activated on this system.

24.7.1 Additional Security in BNU UUCP

BNU UUCP provides additional protection, based on login IDs, and a fine control over remote system logins, based on the introduced file named Permissions. In addition, there is also the file named remote.unknown that controls whether or not an unknown system one not listed in the Systems file could log in. The Permissions file has two types of entries: LOGNAME entries gain specific permissions for individual login IDs that are used when remote systems call this system, i.e., this system accesses remote systems. 1. MACHINE entries gain specific permissions for individual systems when this system calls them; i.e., remote systems access this system. 2. 617 Both entries in the Permissions file consist of an arbitrary number of optionvalue pairs of the format: option=value no spaces around = sign Available options are listed in the following table. A class code M or L designates whether an option could be used with a MACHINE or a LOGNAME entry. Option Class Description LOGNAME L Specifies the login IDs to be used by remote systems MACHINE M Specifies systems that the local system can call REQUEST M, L Specifies whether the remote system can request to set up file transfer from this computer default is no SENDFILES L Specifies whether the called system can execute locally queued requests during a session READ M, L Specifies the directories that uucico can use for requesting files default is uucppublic WRITE M, L Specifies the directories that uucico can use for depositing files default is uucppublic NOREAD M, L Exceptions to READ option or default NOWRITE M, L Exceptions to WRITE option or default CALLBACK L Specifies whether or not the local system must call back before transaction occurs default is no COMMANDS M Commands that the remote system can execute locally the keyword ALL grants access to all commands VALIDATE L Used to verify calling systems identity MYNAME M Used to link another system name to the local system PUBDIR M,L Specifies the directory for local access The Permissions file could sound quite confusing, and the best way to explain how it works is by an example. This is presented here, through the presentation of the Permissions files on three arbitrary UUCP systems: blue, red and black. cat etcuucpPermissions ident Permissions 1.6 SMI from SVR4 bnu:Permissions 2.2 per−machine and per−login permissions, e.g., LOGNAME=Usun MACHINE=sun VALIDATE=sun COMMANDS=rmail \ REQUEST=yes SENDFILES=yes See the System and Network Administration Manual for more information. −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− To configure the machine blue: red logs in to blue as Ured, and can request and send files regardless of who started the call. red can read and write to all directories on blue except the blueonly directory, and can execute any command; other machines are not allowed. −− Uncomment following lines on the host blue LOGNAME=Ured MACHINE=red READ=WRITE=COMMANDS=ALL NOREAD= blueonly \ SENDFILES=yes REQUEST=yes 618 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− To configure the machine red: blue logs in to red as Ublue, and can request and send files regardless of who started the call. blue can read and write to all directories on red except the redonly directory, and can execute any command. Any other machine logs in to red as nuucp, and can request files regardless of who started the call, but will send files only when it calls. Other machines can read and write only from the public directory the default, and can execute only the default list of commands. −− Uncomment following lines on the host red LOGNAME=Ublue MACHINE=blue READ=WRITE=COMMANDS=ALL NOREAD=redonly \ SENDFILES=yes REQUEST=yes LOGNAME=nuucp MACHINE=OTHER SENDFILES=yes REQUEST=yes −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− To configure the machine black: red logs in to black as Ured, and can request and send files regardless of who started the call. red can read and write to all directories on black except the blackonly directory, and can execute any command; other machines are not allowed. −− Uncomment following lines on the host black LOGNAME=Ured MACHINE=red READ=WRITE=COMMANDS=ALL NOREAD= blackonly \ SENDFILES=yes REQUEST=yes −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

24.7.2 Additional Security in Version 2 UUCP