The Port Scan Attack Detector (PSAD) is a lightweight system daemon that is designed to work with Linux iptables/firewall code to discover suspicious traffic such as port scans, backdoors, botnet command and control communications, and more. It includes a set of vastly configurable danger thresholds, long-winded alert messages that comprise of the source, destination, scanned port range, begin and end times, TCP flags and equivalent nmap options, reverse DNS info, email and syslog alerting, automatic blocking of offending IP addresses via dynamic configuration of iptables rulesets, passive operating system fingerprinting, and DShield reporting.

Features

• Detection for TCP SYN, FIN, NULL, and XMAS scans as well as UDP scans.
• Support for both IPv4 and IPv6 logs generated by iptables and ip6tables respectively.
• Detection of many signature rules from the Snort intrusion detection system.
• Forensics mode iptables/ip6tables logfile analysis (useful as a forensics tool for extracting scan information from old iptables/ip6tables logfiles).
• Passive operating system fingerprinting via TCP syn packets. Two different fingerprinting strategies are supported; a re-implementation of p0f that strictly uses iptables/ip6tables log messages (requires the –log-tcp-options command line switch), and a TOS-based strategy.
• Email alerts that contain TCP/UDP/ICMP scan characteristics, reverse dns and whois information, snort rule matches, remote OS guess information, and more.
• When combined with fwsnort and the iptables string match extension, psad can generate alerts for application layer buffer overflow attacks, suspicious application commands, and other suspect layer 7 traffic.
• Icmp type and code header field validation.
• Configurable scan thresholds and danger level assignments.
• Iptables rule-set parsing to verify “default drop” policy stance.
• IP/network danger level auto-assignment (can be used to ignore or automatically escalate danger levels for certain networks).
• DShield alerts.
• Auto-blocking of scanning IP addresses via iptables/ip6tables and/or tcpwrappers based on scan danger level. (This feature is NOT enabled by default.)
• Parsing of iptables/ip6tables log messages and generation of CSV output that can be used as input to AfterGlow. This allows iptables/ip6tables logs to be visualized. Gnuplot is also supported.
• Status mode that displays a summary of current scan information with associated packet counts, iptables/ip6tables chains, and danger levels.

Psad also includes a whois client written by Marco d’Itri (see the deps/whois directory).psad generally runs on Linux systems, and is available in the package repositories of many major Linux distributions.

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