How Effective is Multiple-Vantage-Point Domain Control Validation?

Multiple-vantage-point domain control validation (multiVA) is an emerging defense for mitigating BGP hijacks against Web PKI certificate authorities. While adoption of multiVA is growing, little work has quantified its effectiveness against BGP hijacks in the wild. We bridge the gap by presenting the first analysis framework that measures the security of multiVA deployment under a confluence of real-world routing and networking practices (namely, DNS and RPKI). Our framework accurately models the attack surface of multiVA by 1) considering attacks on DNS nameservers involved in domain validation, 2) incorporating deployed practical security techniques such as RPKI, 3) performing fine-grained Internet-scale analysis to compute resilience (i.e., how difficult it is to launch a BGP hijack against a domain and get a bogus certificate under multiVA). We apply our framework to perform a rigorous security analysis of the multiVA deployment of Let's Encrypt, compiling a dataset of 31 billion DNS queries for about 1 million domains over the course of four months. Our analysis shows that while DNS does enlarge the attack surface of multiVA, Let's Encrypt's multiVA deployment still offers an 88% median resilience against BGP hijacks, a notable improvement over the 76% resilience offered by single-vantage-point validation. RPKI, even in its current state of partial deployment, effectively mitigates BGP attacks and improves security of the deployment by 15%. Exploring over 11,000 different multiVA configurations, we find that Let's Encrypt's deployment can be further expanded to achieve a resilience of over 97% with only two additional vantage points in different public cloud providers. In addition to adding these vantage points, moving to a full quorum policy can achieve a maximal resilience of over 99%, motivating a rethinking of multiVA design parameters.