security

[Ben Luey <lueyb@carleton.edu>]

Two security questions:

On a server, I have /etc/hosts.deny ALL:ALL and hosts.allow
ALL: 192.168.1.0/255.255.255.0   --intranet has full access
sshd: ALL      -- everyone has ssh

I ran nmap on this server from outside the intranet and it says lots of
things are open:

Starting nmap V. 2.02 by Fyodor (fyodor@dhp.com, www.insecure.org/nmap/)
Interesting ports on sf-usr4-21-149.dialup.slip.net (207.171.246.149):
Port    State       Protocol  Service
21      open        tcp        ftp
22      open        tcp        unknown
23      open        tcp        telnet
25      open        tcp        smtp
37      open        tcp        time
53      open        tcp        domain
70      open        tcp        gopher
79      open        tcp        finger
80      open        tcp        http
98      open        tcp        linuxconf
109     open        tcp        pop-2
110     open        tcp        pop-3
111     open        tcp        sunrpc
113     open        tcp        auth
137     filtered    tcp        netbios-ns
138     filtered    tcp        netbios-dgm
139     filtered    tcp        netbios-ssn
143     open        tcp        imap
513     open        tcp        login
514     open        tcp        shell
895     open        tcp        unknown                                  

I can't use, say, imap from outside the normal way, but is it still a
security liability, or now? (137-139 are filtered from ppp0). If it is,
what should I do -- (this doesn't have to be very anal, because it is a
dynamic ip dialup, but still -- I noticed someone trying my imap
connection from outside ...) 

Also, how can I have ssh (or telnet) only let certain users login from
ppp0? Some users have wussy passwords which is fine within the network,
but I'd like to disable access to these accounts from the outside (ie
ppp0).

Thanks,

Ben


Ben Luey
lueyb@carleton.edu
ICQ: 19144397

Modern computerized word processing enables us, both as individuals and as a
cohesive societal entity, to exponentially enhance and aggrandize the 
parameters, both qualitative and quantitative, not to mention paradigmatic, of 
out communicative conceptualizations because now we can spell great big words
correctly without having a clue what they mean.  -- Dave Barry