Common Attack Pattern Enumeration and Classification
A Community Resource for Identifying and Understanding Attacks
An attacker sends a UDP packet to a closed port on the target machine to solicit an IP Header's total length field value within the echoed 'Port Unreachable" error message. RFC1122 specifies that the Header of the request must be echoed back when an error is sent in response, but some operating systems and firmware alter the integrity of the original header. Non-standard ICMP/IP implementations result in response that are useful for individuating remote operating system or router firmware versions. There are four general response types that can be used to distinguish operating systems apart.
This type of behavior is useful for building a signature-base of operating system responses, particularly when error messages contain other types of information that is useful identifying specific operating system responses.
Target Attack Surface Description
Targeted OSI Layers: Network Layer
Target Attack Surface Localities
Target Attack Surface Types: Host
Target Functional Services
[R.331.1] [REF-20] Stuart McClure, Joel Scambray and George Kurtz. "Hacking Exposed: Network Security Secrets & Solutions". Chapter 2: Scanning, pg. 56. 6th Edition. McGraw Hill. 2009.
[R.331.2] [REF-23] J. Postel. "RFC792 - Internet Control Messaging Protocol". Defense Advanced Research Projects Agency (DARPA). September 1981. <http://www.faqs.org/rfcs/rfc792.html>.
[R.331.3] [REF-24] R. Braden, Ed.. "RFC1122 - Requirements for Internet Hosts - Communication Layers". October 1989. <http://www.faqs.org/rfcs/rfc1122.html>.
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