Auditing buffer overflow vulnerabilities using hybrid static–dynamic analysis

Dynamic program analysis is extremely successful both in code debugging and in malicious code attacks. Fuzzing, concolic, and monkey testing are instances of the more general problem of analysing programs by dynamically executing their code with selected inputs. While static program analysis has a beautiful and well established theoretical foundation in abstract interpretation, dynamic analysis still lacks such a foundation. In this paper, we introduce a formal model for understanding the notion of precision in dynamic program analysis. It is known that in sound-by-construction static program analysis the precision amounts to completeness. In dynamic analysis, which is inherently unsound, precision boils down to a notion of coverage of execution traces with respect to what the observer (attacker or debugger) can effectively observe about the computation. We introduce a topological characterisation of the notion of coverage relatively to a given (fixed) observation for dynamic program analysis and we show how this coverage can be changed by semantic preserving code transformations. Once again, as well as in the case of static program analysis and abstract interpretation, also for dynamic analysis we can morph the precision of the analysis by transforming the code. In this context, we validate our model on well established code obfuscation and watermarking techniques. We confirm the efficiency of existing methods for preventing control-flow-graph extraction and data exploit by dynamic analysis, including a validation of the potency of fully homomorphic data encodings in code obfuscation.

Buffer overflow is one of the worst program vulnerabilities. Many preventive approaches are applied to mitigate buffer overflow (BOF) vulnerabilities. However, BOF vulnerabilities are still being discovered in programs on a daily basis which might be exploited to crash programs and execute unwanted code at runtime. Monitoring is a popular approach for detecting BOF attacks during program execution and can prevent the consequences of BOF vulnerability exploitations. However, there is no classification of the proposed approaches to understand their common characteristics, objectives, and limitations. In this paper, we classify the current BOF vulnerability monitoring approaches based on the following five characteristics: monitoring objective, program state utilization, implementation mechanism, environmental change, and attack response. The classification will enable researchers to differentiate among existing monitoring approaches. Moreover, it will provide a guideline to choose monitoring approaches suitable for their needs.

A secure software demands effective techniques for vulnerability detection during its development cycle. The practice of detecting security flaws before the deployment phase eliminates the risks that vulnerabilities may impose for the company. Static analysis and dynamic analysis techniques offer two complimentary approaches for checking vulnerabilities. Static analysis involves the scanning of source code or binary eliminating the need of executing it. This approach is fast and has no run time overhead. However, static analysis are quite imprecise and generate huge false positives and false negatives. On the other hand, dynamic analysis involves the running of the software. The problem of false positives and negatives is less in case of dynamic analysis because they analyze by running the test cases. But this approach requires large number of test cases to ensure a certain confidence level in detecting security bugs. This paper describes a methodology which integrates the two approaches in a complimentary manner. It adopts the strengths of the two and eliminates their weaknesses. We are currently dealing with buffer overflow vulnerability with pointer aliasing. However the idea can be extended to other vulnerabilities also for e.g memory related errors, race conditions( Time of Check to Time to Use vulnerability), dangling pointer vulnerability, integer errors etc.

Whitebox fuzzing is a novel form of security testing based on dynamic symbolic execution and constraint solving. Over the last couple of years, whitebox fuzzers have found many new security vulnerabilities (buffer overflows) in Windows and Linux applications, including codecs, image viewers and media players. Those types of applications tend to use floating-point instructions available on modern processors, yet existing whitebox fuzzers and SMT constraint solvers do not handle floating-point arithmetic. Are there new security vulnerabilities lurking in floating-point code?A naive solution would be to extend symbolic execution to floating-point (FP) instructions (months of work), extend SMT solvers to reason about FP constraints (months of work or more), and then face more complex constraints and an even worse path explosion problem. Instead, we propose an alternative approach, based on the rough intuition that FP code should only perform memory safe data-processing of the payload of an image or video file, while the non-FP part of the application should deal with buffer allocations and memory address computations, with only the latter being prone to buffer overflows and other security critical bugs. Our approach combines (1) a lightweight local path-insensitive may static analysis of FP instructions with (2) a high-precision whole-program path-sensitive must dynamic analysis of non-FP instructions. The aim of this combination is to prove memory safety of the FP part of each execution and a form of non-interference between the FP part and the non-FP part with respect to memory address computations.We have implemented our approach using two existing tools for, respectively, static and dynamic x86 binary analysis. We present preliminary results of experiments with standard JPEG, GIF and ANI Windows parsers. For a given test suite of diverse input files, our mixed static/dynamic analysis is able to prove memory safety of FP code in those parsers for a small upfront static analysis cost and a marginal runtime expense compared to regular dynamic symbolic execution.

Buffer overflow vulnerability is the most common and serious type of vulnerability in software today, as network security issues have become increasingly critical. To alleviate the security threat, many vulnerability mining methods based on static and dynamic analysis have been developed. However, the current analysis methods have problems regarding high computational time, low test efficiency, low accuracy, and low versatility. This paper proposed a software buffer overflow vulnerability prediction method by using software metrics and a decision tree algorithm. First, the software metrics were extracted from the software source code, and data from the dynamic data stream at the functional level was extracted by a data mining method. Second, a model based on a decision tree algorithm was constructed to measure multiple types of buffer overflow vulnerabilities at the functional level. Finally, the experimental results showed that our method ran in less time than SVM, Bayes, adaboost, and random forest algorithms and achieved 82.53% and 87.51% accuracy in two different data sets. The method presented in this paper achieved the effect of accurately predicting software buffer overflow vulnerabilities in C/C++ and Java programs.

Buffer overflow is one of the most common types of software vulnerabilities. Various static analysis and dynamic testing techniques have been proposed to detect buffer overflow vulnerabilities. With automatic tool support, static buffer overflow detection technique has been widely used in academia and industry. However, it tends to report too many false positives fundamentally due to the lack of software execution information. Currently, static warnings can only be validated by manual inspection, which significantly limits the practicality of the static analysis. In this paper, we present BovInspector, a tool framework for automatic static buffer overflow warnings inspection and validated bugs repair. Given the program source code and static buffer overflow vulnerability warnings, BovInspector first performs warning reachability analysis. Then, BovInspector executes the source code symbolically under the guidance of reachable warnings. Each reachable warning is validated and classified by checking whether all the path conditions and the buffer overflow constraints can be satisfied simultaneously. For each validated true warning, BovInspector fix it with three predefined strategies. BovInspector is complementary to prior static buffer overflow discovery schemes. Experimental results on real open source programs show that BovInspector can automatically inspect on average of 74.9% of total warnings, and false warnings account for about 25% to 100% (on average of 59.9%) of the total inspected warnings. In addition, the automatically generated patches fix all target vulnerabilities. Further information regarding the implementation and experimental results of BovInspector is available at http://bovinspectortool.github.io/project/. And a short video for demonstrating the capabilities of BovInspector is now available at https://youtu.be/IMdcksROJDg.

Static and dynamic program analysis techniques are important research areas in software security. Static analysis helps us locate vulnerabilities in a software by looking at the source code. Dynamic analysis helps us reason about the behavior of the software from information gathered at run-time. In this thesis, we are focusing on data flow analysis and heap analysis which are key static and dynamic program analysis techniques respectively.
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\nIn the first part of this thesis, we aim at detecting vulnerabilities in Android applications which have capability leaks. The security of the Android platform relies mainly on sandboxing applications and restricting their capabilities such that no application, by default, can perform any operations that would adversely impact other applications, the operating system, or the user. However, a recent research reported that a genuine but vulnerable application may leak its capabilities. When being leveraged, other applications can gain extra capabilities which they are not granted originally. We present DroidChecker, an Android application analyzing tool which searches for the aforementioned vulnerability in Android applications. DroidChecker uses interprocedural control flow graph searching and static taint checking to detect exploitable data paths in an Android application. We analyzed more than 1100 Android applications using DroidChecker and found 6 previously unknown vulnerable applications including the renowned Adobe Photoshop Express application. We also developed a malicious application that exploits the previously unknown vulnerability found in the Adobe Photoshop Express application. We showed that the malicious application, which is not granted any permissions, can access contacts on the phone with just a few lines of code.
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\nIn the second part of this thesis, we explore the use of heap analysis to extract software birthmarks. There are techniques like code obfuscation and watermarking which can make the source code of a program difficult to understand by humans and prove the ownership of the program. However, code obfuscation cannot avoid the source code being copied and a watermark can be defaced. A birthmark is a group of unique characteristics a program possesses that can be used to identify the program. We propose two novel dynamic birthmark systems based on the run-time heap. A dynamic birthmark is one that is extracted when the program is executing. Since it is based on the run-time behavior of the program, semantics-preserving transformations of the code like obfuscation cannot defeat dynamic birthmarks. In this regard, dynamic birthmarks are more robust compared with static birthmarks.
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\nTo the best of our knowledge, these are the first birthmark systems using heap analysis as the underlying technique. The basic idea is to take snapshots of the heap while the program is running. From the snapshots, heap graphs are constructed to model the referencing structure between objects. After going through some filtering and referencing processes, they become the birthmarks. The two birthmark systems have been devised to extract birthmarks for Java programs and JavaScript programs respectively. While the underlying ideas of the two birthmark systems are similar, the differences in nature of the two programming languages led to different implementation designs.

Malware classification plays an important role in tracing the attack sources of computer security. However, existing static analysis methods are fast in classification, but they are inefficient in some malware using packing and obfuscation techniques; the dynamic analysis methods have better universality for packing and obfuscation, but they will cause excessive classification cost. To overcome these shortcomings, in this paper, we propose a classification system Malscore based on the probability scoring and machine learning, which sets the probability threshold to concatenate static analysis (called Phase 1) and dynamic analysis (called Phase 2). The convolutional neural networks with spatial pyramid pooling were used to analyze the grayscale images (static features) in Phase 1, and the variable n-grams and machine learning were used to analyze the native API call sequences (dynamic features) in Phase 2. Malscore combined static analysis with dynamic analysis not only accelerated the static analysis process by taking advantage of the CNN in image recognition but also appeared to be more resilient to obfuscation by the dynamic analysis. Different from other static and dynamic analysis techniques, when malware is detected, due to the fact that malware will most likely be labeled only by static analysis, we could reduce the overheads by dynamically analyzing a few malware that has less obvious features or greater confusion in static analysis. We performed experiments on 174607 malware samples from 63 malware families. The result showed that Malscore achieved 98.82% accuracy for malware classification. Furthermore, Malscore was compared with the method of using static and dynamic analysis. The preprocessing and test time represented a reduction of 59.58% and 61.70%, respectively.

Understanding business processes is an important step for software maintenance. The approaches for recovering business processes are mostly based on source code analysis, including static analysis and dynamic analysis. All these methods are proved to be effective in some specific situations. However, they are challenged when facing enterprise legacy systems which implement complex business processes triggered by the external actors. In this paper, we introduce a new business process recovery approach that combines the requirement reacquisition with dynamic and static program analysis methods. The approach has been applied to the maintenance of an equity trading system to prove its efficiency.

Applications continue to increase in size and complexity which makes debugging and program understanding more challenging. Programs written in managed languages, such as Java, C#, and Ruby, further exacerbate this challenge because they tend to encode much of their state in the heap. This paper introduces dynamic shape analysis, which seeks to characterize data structures in the heap by dynamically summarizing the object pointer relationships and detecting dynamic degree metrics based on class. The analysis identifies recursive data structures, automatically discovers dynamic degree metrics, and reports errors when degree metrics are violated. Uses of dynamic shape analysis include helping programmers find data structure errors during development, generating assertions for verification with static or dynamic analysis, and detecting subtle errors in deployment. We implement dynamic shape analysis in a Java Virtual Machine (JVM). Using SpecJVM and DaCapo benchmarks, we show that most objects in the heap are part of recursive data structures that maintain strong dynamic degree metrics. We show that once dynamic shape analysis establishes degree metrics from correct executions, it can find automatically inserted errors on subsequent executions in microbenchmarks. These suggests it can be used in deployment for improving software reliability.

The past decade has witnessed an explosive increase in the scale, intensity and sophistication of cyber attacks. While software vendors have significantly increased their efforts on security, they are almost always playing catch up. As a result, security-conscious organizations and individuals have come to expect their system administrators to deploy an array of tools and techniques to stay a step ahead of the hackers. While developer-oriented security tools rely mainly on static analysis, runtime analysis and policy enforcement are the mechanisms of choice in administrator-oriented tools. Runtime techniques offer increased automation and precision over static analysis, thus addressing the needs of administrators who don't have the time or resources needed to acquire extensive knowledge about the internals of a software system. In this talk, I will begin by summarizing some of the significant advances that have been achieved in the past few years in the context of software vulnerability mitigation, including buffer overflow defenses, and more recently, the impressive results that have been achieved using dynamic information-flow analysis for blocking the most popular exploits today, including SQL and command injection and cross-site scripting. I will then proceed to describe dynamic analysis and enforcement techniques aimed at another high-profile security problem faced today, namely, malware defense. Our initial target in this regard has been on dynamic analysis techniques for extracting high-level models of program behavior. These models could be used in a variety of applications such as intrusion detection, vulnerability analysis and security policy verification. More recently, interesting advances have been made in the context of security policy development, where a combination of static and dynamic analysis techniques have been developed to synthesize low-level, enforceable policies that achieve a high-level goal such as protecting system integrity. Finally, I will conclude the talk with a discussion of some research opportunities and challenges in software security.

Programming tools have expanded both in scope of the problems they solve, and in the kinds of techniques they use. Traditionally, programming tools have focused on detecting errors in programs. Recently, this scope has broadened to help with other programming tasks, including inferring specifications, helping diagnose root cause of errors during debugging, and managing knowledge in large projects. Also, traditionally programming tools have been based on either static or dynamic program analysis. Modern programming tools combine static and dynamic program analysis together with techniques from other disciplines such as statistical and probabilistic inference, and information retrieval. This paper reports on some such tools built by the Rigorous Software Engineering group at Microsoft Research India.

While memory-safe and type-safe languages have been available for many years, the vast majority of software is still implemented in type-unsafe languages such as C/C++. Despite massive concerted efforts by software vendors such as Microsoft to eliminate buffer overflow vulnerabilities through automated and manual code review, they continue to be found and exploited. We present a novel approach that accepts the existence of overflow vulnerabilities and uses parallelism available through current and future multi-core architectures to detect vulnerabilities by monitoring the parallel execution of several slightly varying instances of the same application. During regular execution each instance performs equivalent computations. When an attacker attempts to inject an attack vector through a buffer overflow vulnerability, however, each instance reacts differently due to the variances we introduced into each instance. We describe our prototype implementation of such a parallelism-based buffer overflow detection system and demonstrate that it is capable of stopping buffer overflow vulnerabilities using actual exploit codes for the popular Apache Web server. The experimental results show that the runtime overhead of our parallel execution framework is less than 10% on average.

Concurrency programs are hard to test or debug due to their non-deterministic nature. Existing dynamic program analysis approaches tried to address this by carefully examine a recorded execution trace. However, developing such analysis tools is complicated, requiring to take care of many tedious implementation details, and comparing and evaluating different analysis approaches are also subject to various biases, due to lack of a common base platform. This motivates us to design DPAC, an infrastructure that support in building dynamic program analysis tools for concurrency Java programs. DPAC takes events and their various processing mechanisms as its underlying model to facilitate monitoring and manipulation of program executions as required by dynamic program analysis. Various analysis tools can be implemented by customizing their required event types and processing mechanisms. We show two concrete case studies how our DPAC helps building existing dynamic program analysis approaches, as well as tuning subtle implementation details for supporting customized function implementation and code transformation.

Analyzing links among pages from different mobile apps is an important task of app analysis. Currently, most efforts of analyzing inter-app page links rely on static program analysis, which produces a lot of false positives, requiring significant manual effort to verify the links. To address the issue, in this paper, we propose LinkRadar, a data-driven approach to assisting the analysis of inter-app page links. Our key idea is to use dynamic program analysis to gather a set of actual inter-app page links, based on which we train a model to predict whether there exist links among pages from different apps to help verify the results of static program analysis. The challenge is that inter-app page links are hard to be triggered by dynamic program analysis, making it difficult to collect enough inter-app page links to train the model. Considering the similarity between intra-app page links and inter-app page links, we use transfer learning to deal with the data scarcity problem. Evaluation results show that LinkRadar is able to infer the inter-app page links with high accuracy.