Common Attack Pattern Enumeration and Classification
A Community Resource for Identifying and Understanding Attacks
An adversary 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: 1) the IP total length field may be calculated correctly, 2) an operating system may add 20 or more additional bytes to the length calculation, 3) the operating system may subtract 20 or more bytes from the correct length of the field or 4) the IP total length field is calculated with any other incorrect value. 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.
The table below 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.
The table below shows the views that this attack pattern belongs to and top level categories within that view.
A tool capable of sending/receiving UDP datagram packets from a remote system to a closed port and receive an ICMP Error Message Type 3, "Port Unreachable..
The table below 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.
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