Probabilistic Modeling and Inference for Obfuscated Network Attack Sequences

Prevalent computing devices with networking capabilities have become critical network infrastructure for government, industry, academia and every-day life. As their value rises, the motivation driving network attacks on this infrastructure has shifted from the pursuit of notoriety to the pursuit of profit or political gains, leading to network attack on various scales. Facing diverse network attack strategies and overwhelming alters, much work has been devoted to correlate observed malicious events to pre-defined scenarios, attempting to deduce the attack plans based on expert models of how network attacks may transpire. We started the exploration of characterizing network attacks by investigating how temporal and spatial features of attack sequence can be used to describe different types of attack sources in real data set. Attack sequence models were built from real data set to describe different attack strategies. Based on the probabilistic attack sequence model, attack predictions were made to actively predict next possible actions. Experiments through attack predictions have revealed that sophisticated attackers can employ a number of obfuscation techniques to confuse the alert correlation engine or classifier. Unfortunately, most exiting work treats attack obfuscations by developing ad-hoc fixes to specific obfuscation technique. To this end, we developed an attack modeling framework that enables a systematical analysis of obfuscations. The proposed framework represents network attack strategies as general finite order Markov models and integrates it with different attack obfuscation models to form probabilistic graphical model models. A set of algorithms is developed to inference the network attack strategies given the models and the observed sequences, which are likely to be obfuscated. The algorithms enable an efficient analysis of the impact of different obfuscation techniques and attack strategies, by determining the expected classification accuracy of the obfuscated sequences. The algorithms are developed by integrating the recursion concept in dynamic programming and the Monte-Carlo method. The primary contributions of this work include the development of the formal framework and the algorithms to evaluate the impact of attack obfuscations. Several knowledge-driven attack obfuscation models are developed and analyzed to demonstrate the impact of different types of commonly used obfuscation techniques. The framework and algorithms developed in this work can also be applied to other contexts beyond network security. Any behavior sequences that might suffer from noise and require matching to pre-defined models can use this work to recover the most likely original sequence or evaluate quantitatively the expected classification accuracy one can achieve to separate the sequences

Hidden Markov Model and Cyber Deception for the Prevention of Adversarial Lateral Movement

Advanced persistent threats (APTs) have emerged as multi-stage attacks that have targeted nation-states and their associated entities, including private and corporate sectors. Cyber deception has emerged as a defense approach to secure our cyber infrastructure from APTs. Practical deployment of cyber deception relies on defenders\u27 ability to place decoy nodes along the APT path optimally. This paper presents a cyber deception approach focused on predicting the most likely sequence of attack paths and deploying decoy nodes along the predicted path. Our proposed approach combines reactive (graph analysis) and proactive (cyber deception technology) defense to thwart the adversaries\u27 lateral movement. The proposed approach is realized through two phases. The first phase predicts the most likely attack path based on Intrusion Detection System (IDS) alerts and network trace, and the second phase is determining optimal deployment of decoy nodes along the predicted path. We employ transition probabilities in a Hidden Markov Model to predict the path. In the second phase, we utilize the predicted attack path to deploy decoy nodes. However, it is likely that the attacker will not follow that predicted path to move laterally. To address this challenge, we employ a Partially Observable Monte-Carlo Planning (POMCP) framework. POMCP helps the defender assess several defense actions to block the attacker when it deviates from the predicted path. The evaluation results show that our approach can predict the most likely attack paths and thwarts the adversarial lateral movement

TANDI: Threat Assessment of Network Data and Information

Current practice for combating cyber attacks typically use Intrusion Detection Sensors (IDSs) to passively detect and block multi-stage attacks. This work leverages Level-2 fu sion that correlates IDS alerts belonging to the same attacker, and proposes a threat assess ment algorithm to predict potential future attacker actions. The algorithm, TANDI, reduces the problem complexity by separating the models of the attacker\u27s capability and opportu nity, and fuse the two to determine the attacker\u27s intent. Unlike traditional Bayesian-based approaches, which require assigning a large number of edge probabilities, the proposed Level-3 fusion procedure uses only 4 parameters. TANDI has been implemented and tested with randomly created attack sequences. The results demonstrate that TANDI predicts fu ture attack actions accurately as long as the attack is not part of a coordinated attack and contains no insider threats. In the presence of abnormal attack events, TANDI will alarm the network analyst for further analysis. The attempt to evaluate a threat assessment algo rithm via simulation is the first in the literature, and shall open up a new avenue in the area of high level fusion

Cyber Deception for Critical Infrastructure Resiliency

The high connectivity of modern cyber networks and devices has brought many improvements to the functionality and efficiency of networked systems. Unfortunately, these benefits have come with many new entry points for attackers, making systems much more vulnerable to intrusions. Thus, it is critically important to protect cyber infrastructure against cyber attacks. The static nature of cyber infrastructure leads to adversaries performing reconnaissance activities and identifying potential threats. Threats related to software vulnerabilities can be mitigated upon discovering a vulnerability and-, developing and releasing a patch to remove the vulnerability. Unfortunately, the period between discovering a vulnerability and applying a patch is long, often lasting five months or more. These delays pose significant risks to the organization while many cyber networks are operational. This concern necessitates the development of an active defense system capable of thwarting cyber reconnaissance missions and mitigating the progression of the attacker through the network. Thus, my research investigates how to develop an efficient defense system to address these challenges. First, we proposed the framework to show how the defender can use the network of decoys along with the real network to introduce mistrust. However, another research problem, the defender’s choice of whether to save resources or spend more (number of decoys) resources in a resource-constrained system, needs to be addressed. We developed a Dynamic Deception System (DDS) that can assess various attacker types based on the attacker’s knowledge, aggression, and stealthiness level to decide whether the defender should spend or save resources. In our DDS, we leveraged Software Defined Networking (SDN) to differentiate the malicious traffic from the benign traffic to deter the cyber reconnaissance mission and redirect malicious traffic to the deception server. Experiments conducted on the prototype implementation of our DDS confirmed that the defender could decide whether to spend or save resources based on the attacker types and thwarted cyber reconnaissance mission. Next, we addressed the challenge of efficiently placing network decoys by predicting the most likely attack path in Multi-Stage Attacks (MSAs). MSAs are cyber security threats where the attack campaign is performed through several attack stages and adversarial lateral movement is one of the critical stages. Adversaries can laterally move into the network without raising an alert. To prevent lateral movement, we proposed an approach that combines reactive (graph analysis) and proactive (cyber deception technology) defense. The proposed approach is realized through two phases. The first phase predicts the most likely attack path based on Intrusion Detection System (IDS) alerts and network trace. The second phase determines the optimal deployment of decoy nodes along the predicted path. We employ transition probabilities in a Hidden Markov Model to predict the path. In the second phase, we utilize the predicted attack path to deploy decoy nodes. The evaluation results show that our approach can predict the most likely attack paths and thwart adversarial lateral movement