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Full Discussion: One Question about security
Special Forums Cybersecurity One Question about security Post 302074189 by hegemaro on Sunday 21st of May 2006 08:23:27 AM
Old 05-21-2006
I have been supporting a dialup BBS -- yes they still exist -- for five years now. Telnet itself is not an inherently insecure protocol nor are most daemon implementations any more buggy than, say, FTP. Stay current with patches and you'll be fine on that point. There are two issues that you must consider:

1 ) Transmission of account and password information in plain text
Since the server is Internet facing, it is quite possible that someone could intercept a valid user's account/password information and use it for nefarious activities. Depending on your server configuration, that account may also grant the intruder access to through other services such as FTP or mail.
2 ) Shell access to the server.
Unlike HTTP which can more readily be limited to specific areas of the system, shell access throws open the floodgates to your system and any weaknesses in configuration. Using restricted shells does little as there are numerous ways to bypass that limited security.
Here are some ideas:

As System Shock suggested, Secure Shell can completely address Issue #1 by encrypting not only the data stream once logged in but also the account information as the user logs in. It is freely available from http://www.openssh.org/. It is moderately complex to compile and configure but it will integerate seamlessly with your existing application; it is simply a replacement for Telnet not the application already running on the system.

The down-side is that it requires your users to use an SSH client to connect to your server. Telnet and Hyperterminal will no longer work. This can be a deal-breaker.

The second issue can be addressed with a "change root" jail in which the user is locked into a subdirectory structure of the entire file system. I have no direct experience myself but the http://www.jmcresearch.com/projects/jail/ reference has been suggested. There may be issues integrating with your application but I can not say what they would be.

So, what to do?

The most important thing is to harden your server to the point of paranoia. There are many documents on how this can be achieved but here are a few general suggestions.
  • Disable ALL unnecessary network services ideally leaving Telnet only.
  • Lock all system accounts except root, of course, restricting root access to the console only.
  • Enforce a strict password policy with an 8-character minimum length and frequent password changes.
  • Isolate your server from the rest of your network. Firewalls work fine but physical isolation is not susceptible to configuration errors. To simplify periodic access to the server, a second interface can be added with a cross-over connection to another server. On your Internet facing system, the interface can be left up while on the cross-over server, bring down the interface when not in use.
  • PATCHES!! Stay on top of all security patches for your environment. This is most important and most overlooked.
 

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LEARN ABOUT HPUX

nfssec

nfssec(5)							File Formats Manual							 nfssec(5)

NAME

       nfssec - overview of NFS security modes

DESCRIPTION

       The  mount_nfs(1M)  and	share_nfs(1M) commands each provide a way to specify the security mode to be used on an NFS filesystem through the
       option.	mode can be either or These security modes may also be added to the automount maps.  Note that mount_nfs(1M) and automount(1M)	do
       not support at this time.

       The  option  on	the share_nfs(1M) command line establishes the security mode of NFS servers.  If the NFS connection uses the NFS Version 3
       protocol, the NFS clients must query the server for the appropriate mode to use.  If the NFS connection uses the NFS  Version  2  protocol,
       then  the NFS client uses the default security mode, which is currently NFS clients may force the use of a specific security mode by speci-
       fying the option on the command line.  However, if the filesystem on the server is not shared with that security mode, the  client  may	be
       denied access.

       If  the	NFS client wants to authenticate the NFS server using a particular (stronger) security mode, the client wants to specify the secu-
       rity mode to be used, even if the connection uses the NFS Version 3 protocol.  This guarantees that an attacker masquerading as the  server
       does not compromise the client.

       The  NFS security modes are described below.  Of these, the modes use the Kerberos V5 protocol for authenticating and protecting the shared
       filesystems.  Before these can be used, the system must be configured to be part of a Kerberos realm.

       Use	 authentication.  The user's UNIX user-id and group-ids are passed in the clear on the network, unauthenticated by the NFS  server
		 .  This is the simplest security method and requires no additional administration.  It is the default used by HP-UX NFS Version 2
		 clients and HP-UX NFS servers.

       Use a Diffie-Hellman public key system
		 which is referred to as in the forthcoming Internet RFC).

       Use Kerberos V5 protocol to authenticate users before granting access
		 to the shared filesystem.

       Use Kerberos V5 authentication with integrity checking (checksums) to
		 verify that the data has not been tampered with.

       User Kerberos V5 authentication, integrity checksums, and privacy protection
		 (encryption) on the shared filesystem.  This provides the most secure filesystem sharing, as all traffic is encrypted.  It should
		 be  noted  that  performance  might  suffer on some systems when using depending on the computational intensity of the encryption
		 algorithm and the amount of data being transferred.

       Use null authentication
		 NFS clients using have no identity and are mapped to the anonymous user by NFS servers.  A client using  a  security  mode  other
		 than the one with which an HP-UX NFS server shares the filesystem has its security mode mapped to In this case, if the filesystem
		 is shared with users from the client are mapped to the anonymous user.

WARNINGS

       lists the NFS security services.  Do not edit this file.  It is not intended to be user-configurable.

FILES

       NFS security service configuration file

SEE ALSO

       automount(1M), mount_nfs(1M), share_nfs(1M), rpc_clnt_auth(3N), secure_rpc(3N), nfssec.conf(4).

																	 nfssec(5)
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