What should go into a security-checking shell script?

[John Kimball]

>Re: What should go into a security-checking shell script?

Here's the list which I've been maintaining.  Apologies for the terseness.
Some of the stuff is BSD/Sun specific.  I have a script (with associated
programs) which checks most of these;  it's pretty raw yet.

*** Compare the attributes of "critical" files against a snapshot taken
    at a certain time.
       Attributes to check:
	   uid, gid	
	   permissions	
	   modification time	
	   number of links	
	   checksum / CRC	
	   size		
	Files to check:
            /vmunix
            any suid/sgid
            /bin/* , /usr/ucb/* , /usr/bin/*
            /etc/*
            /usr/etc/*
            /usr/local/* (?)
            /usr/lib/many-things
  	    /usr/lib/uucp/many-things
            /usr/include/many-things
            /lib/many-things

***   scan all files for dangerous combinations of file attributes
	SUIDs, SGID
	    SUIDs, SGIDs writable by group,other	
	    SUIDs, SGIDs owned by system ids but not in system bins/libs	
	    any SUIDs in non-system (ie user) areas
	special files
	    block special files readable/writable by group,other 
	    char special files readable/writable by group,other  
	      (excluding ttys, sigh)
	    block/char special files not in /dev	             
	writable system files
	    system directories writable by other, or by group      
	      (excluding tmp directories, uucppublic)
	    system files writable by other/group    
	      (excluding tmp directories, uucppublic)
            writable binaries, writeable stuff in /etc
        certain readable system files              
            syslog*!                                        
	    crontab, /dev/mem, /dev/kmem, and L.sys shouldn't be          
              other-readable. 
	user startup files
	    user startup files writable by group/other	     
		(.login, .cshrc, .profile, .exrc, .mailrc, .emacs,
                 .logout)
	    user .exrc files in directories writable by group/other 
        user dirs writable by group/other
	user files writable by other			      

***  scan for dangerous attributes within critical files (and yp maps)
	/etc/passwd
	    users without passwords				
	       including uucp!
	    users with same uid					
               including non-root accounts with uid 0!
            guest accounts                                      
            blank lines, ::0:0::                                
	    number of fields 
	    length of fields (ie number of characters in field)
	/etc/group
  	    users in administrative groups (eg, bin)		
	    number of fields 
	    length of fields (ie number of characters in field)
        crontab
	    reduce number of things run as root (su to news, etc, instead)
	/etc/servers                                            
            Only run the minimum number of servers you need.
	    rpc.rexd is bad news
        /usr/lib/uucp/USERFILE                                  
            only /usr/spool/uucppublic should be readable/writable for
	      incoming uucps
        /usr/lib/uucp/L.cmds                                    
            only rmail and rnews should be uuxqtable
	/.rhosts, /etc/hosts.equiv 
  	  look for nonlocal hosts, '+'.
        /etc/securetty or /etc/ttytab
	  disallow root login on most/all terminals
        /etc/netgroup, /etc/exports
        /.profile, /.cshrc, /.login                             
            check for bad PATH (have *no* ., or . as last!)
	look for bad user PATHs                                 
        look for user .rhosts files mentioning external hosts            

***  scan for untoward users
	stale logins (users who haven't logged in for a long time)
        trivial passwords
	   It's best to catch these at password-changing time, but
	     password guessers are also available.

***  scan for odd activity
        last: look for logins/ftps by sync, daemon, sysdiag, etc.
        ps: look for cpu-eaters, etc 

***  dangerous filenames                                        
        user .rhost files
	   disallow if feasible
        su,login,passwd,crypt in strange places

*** monitor the various logs
        search the uucp logs, the syslog logs, etc, for oddities.