sshdfilter automatically blocks ssh brute force attacks by reading sshd log output in real time and adding iptables rules based on authentication failures. Block rules are created by logging on with an invalid user name, or wrongly guessing the password for an existing account. Block rules are removed after a week to maintain a small list of blocks. It also comes with a LogWatch filter.
Arno's IPTABLES Firewall Script is a secure stateful firewall for both single and multi-homed machines. It supports NAT and SNAT, port forwarding, ADSL ethernet modems with both static and dynamically assigned IPs, MAC address filtering, stealth port scan detection, DMZ support, protection against SYN/ICMP flooding, experimental IPv6 support, multi-interface/aliased-IP support, and extensive user definable logging with rate limiting to prevent log flooding. It has plugin support to add extra features (like SSH Brute Force protection and (Racoon) IPSEC support). It is easy to configure and highly customizable. A filter script that makes your firewall log more readable is also included.
sslh accepts connections in HTTP, HTTPS, SSH, OpenVPN, tinc, XMPP, or any other protocol that can be tested using a regular expression, on the same port. This makes it possible to connect to any of these servers on port 443 (e.g. from inside corporate firewalls, which almost never block port 443) while still serving HTTPS on that port. sslh supports IPv6, privilege dropping, transparent proxying, and much more.
fwsnort translates snort rules into an equivalent iptables ruleset. By making use of the iptables string match module, fwsnort can detect application layer signatures which exist in many snort rules. fwsnort adds a --hex-string option to iptables, which allows snort rules that contain hex characters to be input directly into iptables rulesets without modification. In addition, fwsnort makes use of the IPTables::Parse Perl module in order to (optionally) restrict the snort rule translation to only those rules that specify traffic that could potentially be allowed through an existing iptables policy.
The Userspace Logging Daemon (ulogd) is a flexible framework for extensive logging of packets on a firewall machine. ulogd uses the ULOG target of iptables/netfilter, the packet filtering framework of Linux 2.4 and 2.6. It supports binary plugins for adding packet interpreters and output-targets (e.g., for logging into databases, user-defined filetypes, etc.).
Dante is a free implementation of the proxy protocols SOCKS version 4 and SOCKS version 5 (RFC 1928). It can be used as a firewall between networks, controlling outgoing traffic. The package consists of two parts: a socks server and a proxy client that supports socks, HTTP proxies, and UPnP. RFC 1961 (GSSAPI) is supported in both the client and the server. Commercial support is available.