Security

The most critical issue with Portsmith security is that the web server is permanently accessible, more particularly so because it uses the PHP scripting language. If an attacker can compromise the authentication feature because of a vulnerability in the programming or the PHP language itself, the whole network becomes vulnerable.

The database link is another potential target. For example, imagine a black hat launching an SQL injection attack to "modify" the ruleset, making the protection the firewall is supposed to provide fairly useless.

Although research into Portsmith's PHP has not revealed any potential vulnerabilities, one cannot rule out the possibility of a successful attack. It goes without saying that you should update often. For more protection, you might also want to install Suhosin [8] or ModSecurity [9] to give you some defense against zero-day exploits.

The system is based on allowing an authenticated client's IP address for a connection. The source IP arriving at port 443 on the web server is referenced to ascertain the address. This behavior is also a potential source of danger: In the simplest case, the client might be unaware that it is hiding behind a proxy that sets up a connection to the Portsmith firewall for the web browser. This would lead to the proxy address, rather than the client address, being enabled. In turn, this scenario means that any user on the proxy is assigned the same privileges as the user client-side and, thus, can access the client user's resources.

A situation in which an attacker works through a compromised proxy server would be even worse. Considering how long the period of access is granted, this would again leave a gaping hole open for attacks.

Practical Supplement

Portsmith is a practical supplement to a conventional firewall. The solution adds dynamic, predefined enabling to the traditionally static ruleset, allowing users to initiate changes. One potential use would be hardening access to an internal web mailer or other services, such as Sun Secure Global Desktop [10]. With encrypted connections, Portsmith could serve as a VPN replacement. If you prefer a genuine VPN solution, you can easily add IPSec software, such as strongSwan [11] or OpenVPN [12].

Simply using Portsmith to grant SSH firewall access to a restricted group of users is very much over the top. Port knocking [13] is a simpler and more secure alternative. Users with dynamic IP addresses need to rely on manual techniques or an external tool such as a DynDNS service to update the configuration with an active, official IP address.

The default ruleset poses a couple of questions and could definitely be improved in places. Fortunately, changes are made easily, although a change does require manual editing of the Portsmith configuration files. Manual editing can cause complications when you update.

With respect to authentication, Portsmith unfortunately relies on its own database-oriented approach. Use of an RSA token system or single sign-on would be preferable. This would not only mean more convenience for the user, but (especially in the case of RSA) also an extra layer of security.

It would also be useful to introduce time-based controls to automatically lock temporary accounts, for example, or restrict logins to normal office hours for some users. One would hope that the system is flexible enough to support extensions of this kind.

Conclusion

All told, and assuming a working basic configuration and more hardening, Portsmith is a useful extension to any iptables-based firewall that is likely to make life easier for both administrators and users.

Chain INPUT (policy DROP 22 packets, 3590 bytes)
 pkts bytes target     prot opt in     out     source               destination
    7   476 ACCEPT     all  --  eth1   *       192.168.2.0/24       0.0.0.0/0
  200 17460 ACCEPT     all  --  lo     *       127.0.0.1            0.0.0.0/0
    0     0 ACCEPT     tcp  --  eth0   *       0.0.0.0/0            0.0.0.0/0           limit: avg 5/sec burst 5 tcp dpt:80
    0     0 ACCEPT     tcp  --  eth0   *       0.0.0.0/0            0.0.0.0/0           limit: avg 5/sec burst 5 tcp dpt:25
    0     0 ACCEPT     tcp  --  eth0   *       0.0.0.0/0            0.0.0.0/0           limit: avg 5/sec burst 5 tcp dpt:443
    0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
    1    62 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           limit: avg 15/sec burst 5 udp spt:53 state RELATED,ESTABLISHED
    0     0 ACCEPT     icmp --  *      *       192.168.2.0/24       0.0.0.0/0           limit: avg 5/sec burst 5
Chain FORWARD (policy DROP 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
    0     0 ACCEPT     all  --  *      *       192.168.2.0/24       0.0.0.0/0
    0     0 ACCEPT     all  --  *      *       127.0.0.1            0.0.0.0/0
    0     0 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED
Chain OUTPUT (policy ACCEPT 233 packets, 21730 bytes)
 pkts bytes target     prot opt in     out     source               destination