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For decades, the Network Time Protocol (NTP) has been used to synchronize computer clocks over untrusted network paths. This work takes a new look at the security of NTP’s datagram protocol. We argue that NTP’s datagram protocol in RFC5905 is both underspecified and flawed. The NTP specifications do not sufficiently respect (1) the conflicting security requirements of different NTP modes, and (2) the mechanism NTP uses to prevent off-path attacks. A further problem is that (3) NTP’s control-query interface reveals sensitive information that can be exploited in off-path attacks. We exploit these problems in several attacks that remote attackers can use to maliciously alter a target’s time. We use network scans to find millions of IPs that are vulnerable to our attacks. Finally, we move beyond identifying attacks by developing a cryptographic model and using it to prove the security of a new backwards-compatible client/server protocol for NTP.

Cross-site scripting (XSS) vulnerabilities are among the most common and serious web application vulnerabilities. It is challenging to eliminate XSS vulnerabilities because it is difficult for web applications to sanitize all user input appropriately. We present Noncespaces, a technique that enables web clients to distinguish between trusted and untrusted content to prevent exploitation of XSS vulnerabilities. Using Noncespaces, a web application randomizes the the (X)HTML tags and attributes in each document before delivering it to the client. As long as the attacker is unable to guess the random mapping, the client can distinguish between trusted content created by the web application and untrusted content provided by an attacker. To implement Noncespaces with minimal changes to web applications, we leverage a popular web application architecture to automatically apply Noncespaces to static content processed through a popular PHP template engine. We design a policy language for Noncespaces, implement a training mode to assist policy development, and conduct extensive security testing of a generated policy for two large web applications to show the effectiveness of our technique.

In this chapter we describe the design, development and application of the Helix Metamorphic Shield (HMS). The HMS: (1) continuously shifts the program’s attack surface in both the spatial and temporal dimensions, and (2), reduces the program’s attack surface by applying novel evolutionary algorithms to automatically repair vulnerabilities. The symbiotic interplay between shifting and reducing the attack surface results in the automated evolution of new program variants whose quality improves over time.

16th ACM Conference on Computer and Communications Security, CCS'09; Chicago, IL; United States; 9 November 2009 through 13 November 2009, Most cryptographic algorithms provide a means for secret and authentic communication. However, under many circumstances, the ability to repudiate messages or deny a conversation is no less important than secrecy and authenticity. For whistleblowers, informants, political dissidents and journalists - to name a few - it is most important to have means for deniable conversation, where electronic communication must mimic face-to-face private meetings. Off-the-Record Messaging, proposed in 2004 by Borisov, Goldberg and Brewer, and its subsequent improvements, simulate private two-party meetings. Despite some attempts, the multi-party scenario remains unresolved. In this paper, we first identify the properties of multi-party private meetings. We illustrate the differences not only between the physical and electronic medium but also between two- and multi-party scenarios, which have important implications for the design of private chatrooms. We then propose a solution to multi-party off-the-record instant messaging that satisfies the above properties. Our solution is also composable with extensions that provide other properties, such as anonymity. Copyright 2009 ACM.