An adversary engages in TCP Window scanning to analyze port status and operating system type. TCP Window scanning uses the ACK scanning method but examine the TCP Window Size field of response RST packets to make certain inferences. While TCP Window Scans are fast and relatively stealthy, they work against fewer TCP stack implementations than any other type of scan. Some operating systems return a positive TCP window size when a RST packet is sent from an open port, and a negative value when the RST originates from a closed port. TCP Window scanning is one of the most complex scan types, and its results are difficult to interpret. Window scanning alone rarely yields useful information, but when combined with other types of scanning is more useful. It is a generally more reliable means of making inference about operating system versions than port status.
This table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
Standard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.
An adversary sends TCP packets with the ACK flag set and that are not associated with an existing connection to target ports.
An adversary uses the response from the target to determine the port's state. Specifically, the adversary views the TCP window size from the returned RST packet if one was received. Depending on the target operating system, a positive window size may indicate an open port while a negative window size may indicate a closed port.
TCP Window 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.
The ability to send TCP segments with a custom window size 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.
This table specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
Bypass Protection Mechanism
A Related Weakness relationship associates a weakness with this attack pattern. Each association implies a weakness that must exist for a given attack to be successful. If multiple weaknesses are associated with the attack pattern, then any of the weaknesses (but not necessarily all) may be present for the attack to be successful. Each related weakness is identified by a CWE identifier.
Exposure of Sensitive Information to an Unauthorized Actor
[REF-33] Stuart McClure, Joel Scambray
and George Kurtz. "Hacking Exposed: Network Security Secrets & Solutions". Chapter 2: Scanning, pg. 55-56. 6th Edition. McGraw Hill. 2009.
[REF-128] Defense Advanced Research Projects Agency Information Processing Techniques Office and
Information Sciences Institute University of Southern California. "RFC793 - Transmission Control Protocol". Defense Advanced Research Projects Agency (DARPA). 1981-09.
[REF-34] Gordon "Fyodor" Lyon. "Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning". Section 5.8 TCP Window Scan, pg. 115. 3rd "Zero Day" Edition,. Insecure.com LLC, ISBN: 978-0-9799587-1-7. 2008.