TCP Timestamp Policy Filtering for Intrusion Detection
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Solution Overview
Problem
Intrusion detection and prevention systems (IDS/IPS) using single methods for analyzing TCP segments based on timestamps may fail to detect attacks that manipulate TCP timestamp values, as they do not account for differences in how various operating systems reassemble payloads, allowing attackers to evade detection.
Innovation Solution
Implementing a method that identifies a timestamp policy corresponding to the target operating system, using a baseline timestamp from a three-way handshake to filter TCP segments, ensuring that only valid timestamps are forwarded, and updating the baseline timestamp as necessary based on sequence numbers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single method is used for analyzing TCP segments based on timestamps, then the analysis process is simple, but the system fails to detect attacks that manipulate TCP timestamp values
Solution Approach 1:
The system dynamically adapts its analysis method based on the target operating system identified. Different timestamp analysis methods are applied depending on the target OS, making the system flexible and adaptable rather than static and uniform. This resolves the contradiction by allowing complexity to increase only when necessary for specific targets.
Solution Approach 2:
The system changes the analysis parameters (timestamp validation rules) based on the identified target operating system. By adjusting the timestamp analysis parameters to match the target OS behavior, the system achieves higher detection accuracy without applying unnecessary complexity to all targets uniformly.
2Reliability
If multiple timestamp policies are implemented to match different operating systems, then intrusion detection accuracy improves, but the system complexity increases
Solution Approach 1:
The system performs preliminary identification of the target operating system before applying timestamp analysis. By determining the target OS first (through fingerprinting or other identification methods), the system can then select the appropriate timestamp policy, avoiding the need to implement and manage all possible policies simultaneously for all targets.
Solution Approach 2:
Different timestamp analysis policies are applied locally to match each target operating system's specific behavior. Rather than using a single uniform policy globally, the system tailors the timestamp validation rules to the local characteristics of each target OS, improving accuracy without requiring the entire system to be overly complex.
3Object-affected harmful factors
If TCP segments are filtered based on timestamp comparison with baseline, then segments with manipulated timestamps are blocked, but legitimate segments may be incorrectly filtered
Solution Approach 1:
The system uses feedback from the target operating system's actual timestamp handling behavior to refine its filtering decisions. By observing how the target OS processes timestamps and incorporating that information into the filtering logic, the system reduces false positives while maintaining protection against manipulated timestamps.
Solution Approach 2:
The system replicates the target operating system's timestamp validation behavior in its filtering process. By copying the target OS's timestamp handling logic, the system ensures that its filtering decisions match what the target would accept, thereby reducing incorrect filtering of legitimate segments while blocking attacks that would also be rejected by the target.
Data Source
AI summary
A method performed in an intrusion detection/prevention system, a system or a device for determining whether a transmission control protocol (TCP) segment in a TCP connection in a communication network is acceptable. The TCP connection can include TCP segments beginning with a three way handshake. A TCP segment can include a field for a timestamp. A timestamp policy of plural timestamp policies is identified, the timestamp policy corresponding to a target associated with the segments in a TCP connection. A baseline timestamp is identified based on a three way handshake in the TCP connection. Segments in the TCP connection are monitored. The segments in the TCP connection are filtered as indicated in the timestamp policy corresponding to the target, the timestamp policy indicating whether the segments are to be filtered out or forwarded to the target by comparing the timestamp of the segments to the baseline timestamp.