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. 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.

Related CWE definitions

The product provides different responses to incoming requests in a way that reveals internal state information to an unauthorized actor outside of the intended control sphere.
Please note that CAPEC definitions are provided as a quick reference only. Visit for a complete list of CAPEC entries and more information.
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