TCP Sequence Number Probe
Attack Pattern ID: 321 (Detailed Attack Pattern)Typical Severity: LowStatus: Draft
+ Description

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

Server-side

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.
ACK
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.
ACK
Related Protocol: Internet Protocol
Relationship Type
Uses Protocol
+ Attack Prerequisites

The ability to send an TCP ACK segment to an open port and receive a response back containing a TCP sequence number.

+ Related Attack Patterns
NatureTypeIDNameDescriptionView(s) this relationship pertains toView\(s\)
ChildOfAttack PatternAttack Pattern315TCP/IP Fingerprinting Probes 
Mechanism of Attack (primary)1000
+ References
Stuart McClure, Joel Scambray and George Kurtz. "Hacking Exposed: Network Security Secrets & Solutions". 6th Edition. McGraw Hill, ISBN: 978-0-07-161374-3. 2009.
Defense Advanced Research Projects Agency (DARPA). "RFC793 - Transmission Control Protocol". 1981. <http://www.faqs.org/rfcs/rfc793.html>.
Gordon "Fyordor" Lyon. "Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning". 3rd "Zero Day" Edition, . Insecure.com LLC, ISBN:978-0-9799587-1-7. 2008.
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