Endpoint NTLM Baseline for Pass-the-Hash Detection
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Solution Overview
Problem
The NTLM authentication protocol is vulnerable to Pass-the-Hash attacks, where attackers use stolen password hashes to impersonate users, and existing systems lack effective detection mechanisms for such attacks, particularly in non-standard implementations.
Innovation Solution
Creating a baseline of expected behavior for each endpoint to detect deviations from standard NTLM protocol implementations, using an agent to monitor and fingerprint system activities, including hash functions, version strings, and feature flags, to identify anomalous behavior indicative of Pass-the-Hash attacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If NTLM authentication protocol is used for network security, then user authentication is enabled, but the system becomes vulnerable to Pass-the-Hash attacks
Solution Approach 1:
The system performs preliminary actions by establishing a baseline of expected NTLM protocol behavior before attacks occur. This baseline includes expected response patterns, timing characteristics, and authentication sequences. By having this reference established in advance, the system can detect deviations indicating PTH attacks without requiring real-time analysis of attack patterns.
Solution Approach 2:
The system implements continuous feedback by monitoring NTLM authentication exchanges and comparing actual behavior against the established baseline. When deviations are detected (such as unexpected authentication responses or anomalous timing), the system provides feedback that triggers alerting and further investigation. This closed-loop monitoring enables dynamic detection of PTH attacks while maintaining normal authentication operations.
2Difficulty of detecting and measuring
If detection mechanisms are added to identify PTH attacks, then attack detection capability is improved, but system complexity increases
Solution Approach 1:
The detection mechanism leverages the existing NTLM authentication infrastructure and protocol exchanges to gather detection data. Rather than requiring separate complex detection systems, the authentication protocol itself provides the necessary information streams. The baseline comparison approach uses self-generated reference data from legitimate authentication sequences, eliminating the need for external training datasets or complex machine learning models.
Solution Approach 2:
The system detects attacks by monitoring changes in protocol parameters such as response timing, message sequences, and authentication token characteristics. By establishing baseline parameter ranges from legitimate operations and detecting deviations outside these ranges, the system achieves effective detection through simple parameter comparison rather than complex analysis. This approach transforms a complex detection problem into straightforward parameter threshold checking.
Data Source
AI summary
A method of generating a baseline of expected behavior on a single machine or endpoint to accurately fingerprint the native behavior of the NTLM protocol on that particular endpoint in a network. By limiting the scope of a baseline to a single endpoint, the scope of the baseline can consist of expected behavior (including supported hash functions, version strings and various feature flags). Deviations from these behaviors are considered evidence of a redundant implementation of NTLM utilized by an attacker and thus as evidence of an attempted PTH attack. Using this method it is possible to accurately detect PTH attacks originating from all publicly known non-standard implementations of NTLM existing in tools such as Impacket, Metasploit, and Invoke-TheHash.