Détail du CAPEC-302

An adversary uses a TCP FIN scan to determine if ports are closed on the target machine. This scan type is accomplished by sending TCP segments with the FIN bit set in the packet header. The RFC 793 expected behavior is that any TCP segment with an out-of-state Flag sent to an open port is discarded, whereas segments with out-of-state flags sent to closed ports should be handled with a RST in response. This behavior should allow the adversary to scan for closed ports by sending certain types of rule-breaking packets (out of sync or disallowed by the TCB) and detect closed ports via RST packets.

Flux d'exécution

An adversary sends TCP packets with the FIN flag but not associated with an existing connection to target ports.

An adversary uses the response from the target to determine the port's state. If no response is received the port is open. If a RST packet is received then the port is closed.

Conditions préalables

FIN scanning requires the use of raw sockets, and thus cannot be performed from some Windows systems (Windows XP SP 2, for example). On Unix and Linux, raw socket manipulations require root privileges.

Ressources nécessaires

This attack pattern requires the ability to send TCP FIN segments to a host during network reconnaissance. This can be achieved via the use of a network mapper or scanner, or via raw socket programming in a scripting language. Packet injection tools are also useful for this purpose. Depending upon the method used it may be necessary to sniff the network in order to see the response.

Atténuations

FIN scans are detected via heuristic (non-signature) based algorithms, much in the same way as other scan types are detected. An IDS/IPS system with heuristic algorithms is required to detect them.

Faiblesses connexes

Références

REF-33

Hacking Exposed: Network Security Secrets & Solutions
Stuart McClure, Joel Scambray, George Kurtz.

REF-128

RFC793 - Transmission Control Protocol
Defense Advanced Research Projects Agency Information Processing Techniques Office, Information Sciences Institute University of Southern California.
http://www.faqs.org/rfcs/rfc793.html

REF-147

Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning
Gordon "Fyodor" Lyon.

REF-130

The Art of Port Scanning
Gordon "Fyodor" Lyon.
http://phrack.org/issues/51/11.html

Soumission

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