TCP Segment Reassembly for Intrusion Detection
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Solution Overview
Problem
Intrusion detection systems (IDS) face challenges in accurately analyzing TCP segments due to differences in reassembly methods across various operating systems, leading to potential evasion of malicious traffic, as they may not process network traffic in the same manner as the destination host, and existing reassembly policies are incomplete, particularly in handling overlapping segments.
Innovation Solution
Implementing a method that monitors and reassembles TCP segments in a communication network using segment reassembly policies specific to the destination, which can handle non-overlapped, partially overlapped, and completely overlapped segments, and includes an evaluation of urgent indications, to simulate the reassembly process of the destination system, thereby enhancing the detection and prevention of intrusions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an IDS utilizes a single reassembly method, then the device complexity is reduced, but the measurement precision of malicious traffic detection deteriorates
Solution Approach 1:
The IDS dynamically adapts its reassembly behavior by selecting from multiple reassembly policies based on the characteristics of the incoming TCP segments. The system transitions from a static single-method approach to a dynamic multi-policy approach, where the appropriate reassembly strategy is chosen based on segment overlap patterns, urgency indicators, and other TCP flags, thereby maintaining detection accuracy without requiring permanent complexity in the system architecture.
Solution Approach 2:
The system changes the reassembly parameters (such as overlap handling rules, urgency evaluation criteria, and segment ordering logic) based on the specific characteristics of the TCP traffic being analyzed. By adjusting these parameters according to different reassembly policies, the IDS can accurately detect malicious traffic that would otherwise be missed by a fixed reassembly method, while avoiding the need to permanently implement all possible reassembly variations.
2Measurement precision
If multiple segment reassembly policies are implemented to match destination host behavior, then the detection accuracy improves, but the device complexity increases
Solution Approach 1:
The reassembly policy implementation is segmented into distinct, modular components that handle different aspects of TCP segment reassembly independently. Each policy aspect (such as overlap handling, urgency processing, and segment ordering) is implemented as a separate module that can be independently configured and executed. This modular segmentation allows the IDS to implement multiple reassembly policies without creating an intractably complex monolithic system, as each segment can be managed and optimized separately.
3Reliability
If comprehensive overlap handling is implemented, then the reliability of intrusion detection improves, but the difficulty of detecting and measuring segment characteristics increases
Solution Approach 1:
The system performs preliminary classification and categorization of TCP segments based on their overlap characteristics before applying complex reassembly policies. By pre-identifying segments with comprehensive overlaps and categorizing them according to their overlap patterns, the IDS simplifies the subsequent analysis process. This preliminary action reduces the computational difficulty of detecting and measuring segment characteristics while maintaining reliable intrusion detection, as the complex overlap handling is applied only to identified cases rather than all segments uniformly.
Data Source
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AI summary
A method performed in an intrusion detection/prevention system, a system or a device for analyzing segments in a transmission in a communication network. The transmission includes segments in the same transmission control protocol (TCP) session. Segments in a transmission are monitored. Data in the segments in the transmission are reassembled in an order indicated by a segment reassembly policy, the segment reassembly policy indicating an order specific to at least comprehensively overlapped segments.