NXNSAttack: Recursive DNS Inefficiencies and Vulnerabilities

This paper exposes a new vulnerability and introduces a corresponding attack, the NoneXistent Name Server Attack (NXNSAttack), that disrupts and may paralyze the DNS system, making it difficult or impossible for Internet users to access websites, web e-mail, online video chats, or any other online resource. The NXNSAttack generates a storm of packets between DNS resolvers and DNS authoritative name servers. The storm is produced by the response of resolvers to unrestricted referral response messages of authoritative name servers. The attack is significantly more destructive than NXDomain attacks (e.g., the Mirai attack): i) It reaches an amplification factor of more than 1620x on the number of packets exchanged by the recursive resolver. ii) In addition to the negative cache, the attack also saturates the 'NS' section of the resolver caches. To mitigate the attack impact, we propose an enhancement to the recursive resolver algorithm, MaxFetch(k), that prevents unnecessary proactive fetches. We implemented the MaxFetch(1) mitigation enhancement on a BIND resolver and tested it on real-world DNS query datasets. Our results show that MaxFetch(1) degrades neither the recursive resolver throughput nor its latency. Following the discovery of the attack, a responsible disclosure procedure was carried out, and several DNS vendors and public providers have issued a CVE and patched their systems

Characterizing a Meta-CDN

CDNs have reshaped the Internet architecture at large. They operate (globally) distributed networks of servers to reduce latencies as well as to increase availability for content and to handle large traffic bursts. Traditionally, content providers were mostly limited to a single CDN operator. However, in recent years, more and more content providers employ multiple CDNs to serve the same content and provide the same services. Thus, switching between CDNs, which can be beneficial to reduce costs or to select CDNs by optimal performance in different geographic regions or to overcome CDN-specific outages, becomes an important task. Services that tackle this task emerged, also known as CDN broker, Multi-CDN selectors, or Meta-CDNs. Despite their existence, little is known about Meta-CDN operation in the wild. In this paper, we thus shed light on this topic by dissecting a major Meta-CDN. Our analysis provides insights into its infrastructure, its operation in practice, and its usage by Internet sites. We leverage PlanetLab and Ripe Atlas as distributed infrastructures to study how a Meta-CDN impacts the web latency

Improving the Security of Critical Infrastructure: Metrics, Measurements, and Analysis

In this work, we propose three important contributions needed in the process of improving the security of the critical infrastructure: metrics, measurement, and analysis. To improve security, metrics are key to ensuring the accuracy of the assessment and evaluation. Measurements are the core of the process of identifying the causality and effectiveness of various behaviors, and accurate measurement with the right assumptions is a cornerstone for accurate analysis. Finally, contextualized analysis essential for understanding measurements. Different results can be derived for the same data according to the analysis method, and it can serve as a basis for understanding and improving systems security. In this dissertation, we look at whether these key concepts are well demonstrated in existing (networked) systems and research products. In the first thrust, we verified the validity of volume-based contribution evaluation metrics used in threat information sharing systems. Further, we proposed a qualitative evaluation as an alternative to supplement the shortcomings of the volume-based evaluation method. In the second thrust, we measured the effectiveness of the low-rate DDoS attacks in a realistic environment to highlight the importance of establishing assumptions grounded in reality for measurements. Moreover, we theoretically analyzed the low-rate DDoS attacks and conducted additional experiments to validate them. In the last thrust, we conducted a large-scale measurement and analyzed the behaviors of open resolvers, to estimate the potential threats of them. We then went beyond just figuring out the number of open resolvers and explored new implications that the behavioral analysis could provide. We also experimentally shown the existence of forwarding resolvers and their behavior by precisely analyzing DNS resolution packets

A matter of degree:characterizing the amplification power of open DNS resolvers

Open DNS resolvers are widely misused to bring about reflection and amplification DDoS attacks. Indiscriminate efforts to address the issue and take down all resolvers have not fully resolved the problem, and millions of open resolvers still remain available to date, providing attackers with enough options. This brings forward the question if we should not instead focus on eradicating the most problematic resolvers, rather than all open resolvers indiscriminately. Contrary to existing studies, which focus on quantifying the existence of open resolvers, this paper focuses on infrastructure diversity and aims at characterizing open resolvers in terms of their ability to bring about varying attack strengths. Such a characterization brings nuances to the problem of open resolvers and their role in amplification attacks, as it allows for more problematic resolvers to be identified. Our findings show that the population of open resolvers lies above 2.6M range over our one-year measurement period. On the positive side, we observe that the majority of identified open resolvers cut out when dealing with bulky and DNSSEC-related queries, thereby limiting their potential as amplifiers. We show, for example, that 59% of open resolvers lack DNSSEC support. On the downside, we see that a non-negligible number of open resolvers facilitate large responses to ANY and TXT queries (8.1% and 3.4% on average, respectively), which stands to benefit attackers. Finally we show that by removing around 20% of potent resolvers the global DNS amplification potential can be reduced by up to 80%

The Rise of Certificate Transparency and Its Implications on the Internet Ecosystem

In this paper, we analyze the evolution of Certificate Transparency (CT) over time and explore the implications of exposing certificate DNS names from the perspective of security and privacy. We find that certificates in CT logs have seen exponential growth. Website support for CT has also constantly increased, with now 33% of established connections supporting CT. With the increasing deployment of CT, there are also concerns of information leakage due to all certificates being visible in CT logs. To understand this threat, we introduce a CT honeypot and show that data from CT logs is being used to identify targets for scanning campaigns only minutes after certificate issuance. We present and evaluate a methodology to learn and validate new subdomains from the vast number of domains extracted from CT logged certificates.Comment: To be published at ACM IMC 201

How India Censors the Web

One of the primary ways in which India engages in online censorship is by ordering Internet Service Providers (ISPs) operating in its jurisdiction to block access to certain websites for its users. This paper reports the different techniques Indian ISPs are using to censor websites, and investigates whether website blocklists are consistent across ISPs. We propose a suite of tests that prove more robust than previous work in detecting DNS and HTTP based censorship. Our tests also discern the use of SNI inspection for blocking websites, which is previously undocumented in the Indian context. Using information from court orders, user reports, and public and leaked government orders, we compile the largest known list of potentially blocked websites in India. We pass this list to our tests and run them from connections of six different ISPs, which together serve more than 98% of Internet users in India. Our findings not only confirm that ISPs are using different techniques to block websites, but also demonstrate that different ISPs are not blocking the same websites

Can NSEC5 be practical for DNSSEC deployments?

NSEC5 is proposed modification to DNSSEC that simultaneously guarantees two security properties: (1) privacy against offline zone enumeration, and (2) integrity of zone contents, even if an adversary compromises the authoritative nameserver responsible for responding to DNS queries for the zone. This paper redesigns NSEC5 to make it both practical and performant. Our NSEC5 redesign features a new fast verifiable random function (VRF) based on elliptic curve cryptography (ECC), along with a cryptographic proof of its security. This VRF is also of independent interest, as it is being standardized by the IETF and being used by several other projects. We show how to integrate NSEC5 using our ECC-based VRF into the DNSSEC protocol, leveraging precomputation to improve performance and DNS protocol-level optimizations to shorten responses. Next, we present the first full-fledged implementation of NSEC5—extending widely-used DNS software to present a nameserver and recursive resolver that support NSEC5—and evaluate their performance under aggressive DNS query loads. Our performance results indicate that our redesigned NSEC5 can be viable even for high-throughput scenarioshttps://eprint.iacr.org/2017/099.pdfFirst author draf