Hybrid Intrusion Detection System: Combining Misuse and Anomaly Detection for Enhanced Security

Hybrid Intrusion Detection System: Combining Misuse and Anomaly Detection for Enhanced Security

This article analyzes the effectiveness of combining two core intrusion detection technologies – misuse-based (M) and anomaly-based (A) – in a hybrid system for detecting malicious URLs.

The Technologies:

• M: A network-based, signature-based system analyzing individual UDP and TCP packets in a stateless manner.* A: A host-based system operating as a browser plugin, analyzing individual URLs on the fly and maintaining state information.

The Hybrid Approach:

Two hybrid schemes are proposed, running M and A in parallel on the same traffic:

1. HE (Either/Or): Triggers an alert if either M or A detects a threat.2. HB (Both): Triggers an alert only if both M and A detect a threat on the same connection (assuming one URL per connection).

Analysis (assuming independent decisions by M and A and ignoring evasion):

• Statement 1: HE will result in a higher false positive rate than scheme HB. Correct. HE is more sensitive as it triggers on either system's alert, increasing the likelihood of false positives.* Statement 2: HB will result in a lower false negative rate than scheme HE. Correct. HB requires both systems to flag a threat, reducing the chance of missing an actual attack and thus, lowering false negatives.* Statement 3: HE will be likely to detect a larger number of known attacks than HB. Correct. With a lower threshold for alerts, HE is more likely to detect known attack patterns identified by either M or A.* Statement 4: HB will be likely to detect a larger number of novel attacks than HE. Incorrect. While HB minimizes false positives, its reliance on both systems for detection makes it less sensitive to novel attack patterns that might be missed by one of the systems.* Statement 5: It’s impossible to tell which hybrid scheme is clearly better without knowing the cost of false positives and the cost of false negatives. Correct. The optimal choice between HE and HB depends on the specific security needs and the associated costs of different types of errors. A higher tolerance for false positives might favor HE, while minimizing false negatives might prioritize HB.

Conclusion:

Combining misuse-based and anomaly-based intrusion detection systems in a hybrid approach offers a powerful strategy for enhancing security. The choice between HE and HB depends on the specific security requirements and the trade-off between accepting higher false positives for broader detection (HE) or minimizing false negatives at the risk of missing some attacks (HB).