Home > CAPEC List > CAPEC-321: TCP Sequence Number Probe (Version 2.11)  

CAPEC-321: TCP Sequence Number Probe

TCP Sequence Number Probe
Definition in a New Window Definition in a New Window
Attack Pattern ID: 321
Abstraction: Detailed
Status: Stable
Completeness: Complete
Presentation Filter:
+ Summary

This OS fingerprinting probe tests the target system's assignment of TCP sequence numbers. One common way to test TCP Sequence Number generation is to send a probe packet to an open port on the target and then compare the how the Sequence Number generated by the target relates to the Acknowledgement Number in the probe packet. Different operating systems assign Sequence Numbers differently, so a fingerprint of the operating system can be obtained by categorizing the relationship between the acknowledgement number and sequence number as follows:

  • 1. The Sequence Number generated by the target is Zero.
  • 2. The Sequence Number generated by the target is the same as the acknowledgement number in the probe
  • 3. The Sequence Number generated by the target is the acknowledgement number plus one
  • 3. The Sequence Number is any other non-zero number.
+ Target Attack Surface

Target Attack Surface Description

Targeted OSI Layers: Transport Layer

Target Attack Surface Localities


Target Attack Surface Types: Host

Target Functional Services

Target Functional Service 1: None
Protocol 1: TCP
Protocol Header 1: TCP Header
Protocol Field NameProtocol Field DescriptionProtocol Operation Code
Sequence Number
The sequence number of the first data octet a TCP segment.
Protocol Header 2: TCP Header
Protocol RFCProtocol Field NameProtocol Field DescriptionProtocol Operation Code
RFC 792
Acknowledgement Number
If the ACK control bit is set this field contains the starting value of the next sequence number the sender of the segment is expecting to receive.
Related Protocol: Internet Protocol
Relationship Type
Uses Protocol
+ Attack Prerequisites
  • The ability to monitor and interact with network communications.

    Access to at least one host, and the privileges to interface with the network interface card.

+ Typical Severity


+ Typical Likelihood of Exploit

Likelihood: Medium

+ Resources Required

A tool capable of sending and receiving packets from a remote system.

+ Attack Motivation-Consequences
ScopeTechnical ImpactNote
Read application data
Bypass protection mechanism
Hide activities
+ References
[R.321.1] [REF-20] Stuart McClure, Joel Scambray and George Kurtz. "Hacking Exposed: Network Security Secrets & Solutions". Chapter 2: Scanning, pg. 55-56. 6th Edition. McGraw Hill. 2009.
[R.321.2] [REF-21] 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). September 1981. <http://www.faqs.org/rfcs/rfc793.html>.
[R.321.3] [REF-22] Gordon "Fyodor" Lyon. "Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning". Chapter 8. Remote OS Detection. 3rd "Zero Day" Edition,. Insecure.com LLC. 2008.
+ Content History
CAPEC Content TeamThe MITRE Corporation2014-06-23Internal_CAPEC_Team
CAPEC Content TeamThe MITRE Corporation2017-05-01Updated Attack_Motivation-Consequences, Attack_Prerequisites, Related_Attack_Patterns, Resources_Required, Typical_Likelihood_of_ExploitInternal

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Page Last Updated or Reviewed: August 04, 2017