Elias Athanasopoulos

Out of Control: Overcoming Control-Flow Integrity

As existing defenses like ASLR, DEP, and stack cookies are not sufficient to stop determined attackers from exploiting our software, interest in Control Flow Integrity (CFI) is growing. In its ideal form, CFI prevents flows of control that were not intended by the original program, effectively putting a stop to exploitation based on return oriented programming (and many other attacks besides). Two main problems have prevented CFI from being deployed in practice. First, many CFI implementations require source code or debug information that is typically not available for commercial software. Second, in its ideal form, the technique is very expensive. It is for this reason that current research efforts focus on making CFI fast and practical. Specifically, much of the work on practical CFI is applicable to binaries, and improves performance by enforcing a looser notion of control flow integrity. In this paper, we examine the security implications of such looser notions of CFI: are they still able to prevent code reuse attacks, and if not, how hard is it to bypass its protection? Specifically, we show that with two new types of gadgets, return oriented programming is still possible. We assess the availability of our gadget sets, and demonstrate the practicality of these results with a practical exploit against Internet Explorer that bypasses modern CFI implementations.

Rage against the virtual machine: hindering dynamic analysis of Android malware

Antivirus companies, mobile application marketplaces, and the security research community, employ techniques based on dynamic code analysis to detect and analyze mobile malware. In this paper, we present a broad range of anti-analysis techniques that malware can employ to evade dynamic analysis in emulated Android environments. Our detection heuristics span three different categories based on (i) static properties, (ii) dynamic sensor information, and (iii) VM-related intricacies of the Android Emulator. To assess the effectiveness of our techniques, we incorporated them in real malware samples and submitted them to publicly available Android dynamic analysis systems, with alarming results. We found all tools and services to be vulnerable to most of our evasion techniques. Even trivial techniques, such as checking the value of the IMEI, are enough to evade some of the existing dynamic analysis frameworks. We propose possible countermeasures to improve the resistance of current dynamic analysis tools against evasion attempts.

Antisocial Networks: Turning a Social Network into a Botnet

Antisocial Networksare distributed systems based on social networking Web sites that can be exploited by attackers, and directed to carry out network attacks. Malicious users are able to take control of the visitors of social sites by remotely manipulating their browsers through legitimate Web control functionality such as image-loading HTML tags, JavaScript instructions, etc.In this paper we experimentally show that Social Network web sites have the ideal properties to become attack platforms. We start by identifying all the properties of Facebook, a real-world Social Network, and then study how we can utilize these properties and transform it into an attack platform against any host connected to the Internet. Towards this end, we developed a real-world Facebook application that can perform malicious actions covertly. We experimentally measured its impact by studying how innocent Facebook users can be manipulated into carrying out a Denial-of-Service attack. Finally, we explored other possible misuses of Facebook and how they can be applied to other online Social Network web sites.

Enhanced CAPTCHAs: using animation to tell humans and computers apart

Completely Automated Public Turing Test to tell Computers and Humans Apart (CAPTCHA) is a –rather– simple test that can be easily answered by a human but extremely difficult to be answered by computers. CAPTCHAs have been widely used for practical security reasons, like preventing automated registration in Web-based services. However, all deployed CAPTCHAs are based on the static identification of an object or text. All CAPTCHAs, from simple ones, like typing the distorted text, to advanced ones, like recognizing an object in an image, are vulnerable to the Laundry attack. An attacker may post the test to a malicious site and attract its visitors to solve the puzzle for her. This paper focuses on sealing CAPTCHAs against such attacks by adding a dimension not used so far: animation. Animated CAPTCHAs do not have a static answer, thus even when they are exposed to laundering, unsuspected visitors will provide answers that will be useless on the attackers side.

A Tough Call: Mitigating Advanced Code-Reuse Attacks at the Binary Level

Current binary-level Control-Flow Integrity (CFI) techniques are weak in determining the set of valid targets for indirect control flow transfers on the forward edge. In particular, the lack of source code forces existing techniques to resort to a conservative address-taken policy that overapproximates this set. In contrast, source-level solutions can accurately infer the targets of indirect calls and thus detect malicious control-flow transfers more precisely. Given that source code is not always available, however, offering similar quality of protection at the binary level is important, but, unquestionably, more challenging than ever: recent work demonstrates powerful attacks such as Counterfeit Object-oriented Programming (COOP), which made the community believe that protecting software against control-flow diversion attacks at the binary level is rather impossible. In this paper, we propose binary-level analysis techniques to significantly reduce the number of possible targets for indirect branches. More specifically, we reconstruct a conservative approximation of target function prototypes by means of use-def analysis at possible callees. We then couple this with liveness analysis at each indirect callsite to derive a many-to-many relationship between callsites and target callees with a much higher precision compared to prior binary-level solutions. Experimental results on popular server programs and on SPEC CPU2006 show that TypeArmor, a prototype implementation of our approach, is efficient - with a runtime overhead of less than 3%. Furthermore, we evaluate to what extent TypeArmor can mitigate COOP and other advanced attacks and show that our approach can significantly reduce the number of targets on the forward edge. Moreover, we show that TypeArmor breaks published COOP exploits, providing concrete evidence that strict binary-level CFI can still mitigate advanced attacks, despite the absence of source information or C++ semantics.

Misusing unstructured p2p systems to perform dos attacks: the network that never forgets

Unstructured P2P systems have gained great popularity in recent years and are currently used by millions of users. One fundamental property of these systems is the lack of structure, which allows decentralized operation and makes it easy for new users to join and participate in the system. However, the lack of structure can also be abused by malicious users. We explore one such attack, that enables malicious users to use unstructured P2P systems to perform Denial of Service (DoS) attacks to third parties. Specifically, we show that a malicious node can coerce a large number of peers to perform requests to a target host that may not even be part of the P2P network, including downloading unwanted files from a target Web Server. This is a classic form of denial-of-service which also has two interesting characteristics: (a) it is hard to identify the originator of the attack, (b) it is even harder to stop the attack. The second property comes from the fact that certain unstructured P2P systems seem to have a kind of “memory”, retaining knowledge about (potentially false) queries for many days. In this paper we present real-world experiments of Gnutella-based DoS attacks to Web Servers. We explore the magnitude of the problem and present a solution to protect innocent victims against this attack.

AndRadar: Fast Discovery of Android Applications in Alternative Markets

Compared to traditional desktop software, Android applications are delivered through software repositories, commonly known as application markets. Other mobile platforms, such as Apple iOS and BlackBerry OS also use the marketplace model, but what is unique to Android is the existence of a plethora of alternative application markets. This complicates the task of detecting and tracking Android malware. Identifying a malicious application in one particular market is simply not enough, as many instances of this application may exist in other markets. To quantify this phenomenon, we exhaustively crawled 8 markets between June and November 2013. Our findings indicate that alternative markets host a large number of ad-aggressive apps, a non-negligible amount of malware, and some markets even allow authors to publish known malicious apps without prompt action.

PixelVault: Using GPUs for Securing Cryptographic Operations

Protecting the confidentiality of cryptographic keys in the event of partial or full system compromise is crucial for containing the impact of attacks. The Heartbleed vulnerability of April 2014, which allowed the remote leakage of secret keys from HTTPS web servers, is an indicative example. In this paper we present PixelVault, a system for keeping cryptographic keys and carrying out cryptographic operations exclusively on the GPU, which allows it to protect secret keys from leakage even in the event of full system compromise. This is possible by exposing secret keys only in GPU registers, keeping PixelVaults critical code in the GPU instruction cache, and preventing any access to both of them from the host. Due to the non-preemptive execution mode of the GPU, an adversary that has full control of the host cannot tamper with PixelVaults GPU code, but only terminate it, in which case all sensitive data is lost. We have implemented a PixelVault-enabled version of the OpenSSL library that allows the protection of existing applications with minimal modifications. Based on the results of our evaluation, PixelVault not only provides secure key storage using commodity hardware, but also significantly speeds up the processing throughput of cryptographic operations for server applications.

Face/Off: Preventing Privacy Leakage From Photos in Social Networks

The capabilities of modern devices, coupled with the almost ubiquitous availability of Internet connectivity, have resulted in photos being shared online at an unprecedented scale. This is further amplified by the popularity of social networks and the immediacy they offer in content sharing. Existing access control mechanisms are too coarse-grained to handle cases of conflicting interests between the users associated with a photo; stories of embarrassing or inappropriate photos being widely accessible have become quite common. In this paper, we propose to rethink access control when applied to photos, in a way that allows us to effectively prevent unwanted individuals from recognizing users in a photo. The core concept behind our approach is to change the granularity of access control from the level of the photo to that of a users personally identifiable information (PII). In this work, we consider the face as the PII. When another user attempts to access a photo, the system determines which faces the user does not have the permission to view, and presents the photo with the restricted faces blurred out. Our system takes advantage of the existing face recognition functionality of social networks, and can interoperate with the current photo-level access control mechanisms. We implement a proof-of-concept application for Facebook, and demonstrate that the performance overhead of our approach is minimal. We also conduct a user study to evaluate the privacy offered by our approach, and find that it effectively prevents users from identifying their contacts in 87.35% of the restricted photos. Finally, our study reveals the misconceptions about the privacy offered by existing mechanisms, and demonstrates that users are positive towards the adoption of an intuitive, straightforward access control mechanism that allows them to manage the visibility of their face in published photos.

SAuth: protecting user accounts from password database leaks

Password-based authentication is the dominant form of access control in web services. Unfortunately, it proves to be more and more inadequate every year. Even if users choose long and complex passwords, vulnerabilities in the way they are managed by a service may leak them to an attacker. Recent incidents in popular services such as LinkedIn and Twitter demonstrate the impact that such an event could have. The use of one-way hash functions to mitigate the problem is countered by the evolution of hardware which enables powerful password-cracking platforms. In this paper we propose SAuth, a protocol which employs authentication synergy among different services. Users wishing to access their account on service S will also have to authenticate for their account on service V, which acts as a vouching party. Both services S and V are regular sites visited by the user everyday (e.g., Twitter, Facebook, Gmail). Should an attacker acquire the password for service S he will be unable to log in unless he also compromises the password for service V and possibly more vouching services. SAuth is an extension and not a replacement of existing authentication methods. It operates one layer above without ties to a specific method, thus enabling different services to employ heterogeneous systems. Finally we employ password decoys to protect users that share a password across services.