How Block Solved DNS Vulnerabilities
Show notes
When companies rapidly migrate to the cloud without strict registrar policies, users often spin up unsanctioned subdomains pointed at third-party services like Vercel or Hugging Face. When those services are spun down but the DNS records remain, it creates "dangling" domains ripe for takeover, a vulnerability that can compromise entire hosted zones, auth tokens, and session cookies.
In this episode, Ashish sits down with Ramesh Ramani, Staff Security Engineer at Block, to discuss how his team reduced their domain takeover bug bounty reports from over 80 in a single submission down to near zero. Ramesh breaks down the complex challenge of DNS attribution, explaining why automating DNS cleanup is impossible without first identifying resource owners and consolidating approved registrars.
We explore the technical architecture behind Block's stateless, AWS-native automation system, which continuously enumerates their external attack surface and routes vulnerable CNAMEs, MX records, and Elastic IPs directly to the responsible application teams. Ramesh also shares his thoughts on the limitations of AI when evaluating least privilege and parsing logs, emphasizing why security engineers still need deterministic signals.
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Questions asked:
(00:00) Introduction: The Threat of Domain and DNS Takeovers(01:50) Ramesh Ramani’s Background and 20-Year Tech Career(04:40) Discovering the DNS Problem During Block’s 2020 Cloud Migration(07:00) The Catalyst: Receiving a Bug Bounty Report with 80+ Vulnerable Domains(09:30) Why Third-Party PaaS Providers Can't Fix Your Dangling CNAMEs(13:10) How M&A Activity Creates Orphaned Route 53 Name Servers(16:30) The Difference Between Hosted Zone, CNAME, and MX Takeovers(20:00) Finding 400 Vulnerable Domains and the Challenge of Attribution(23:00) The Registrar Problem: Stopping Developers from Creating Unsanctioned Zones(27:30) Using AWS Service Control Policies (SCPs) to Enforce Domain Guardrails(30:30) Building a Stateless Serverless Engine for DNS Automation(37:00) Establishing a Single Source of Truth for the External Attack Surface(40:30) Driving Domain Takeover Bug Bounty Reports Down to Zero(44:00) The Limitations of AI for Deterministic Log Analysis and Least Privilege(50:30) Fun Questions, Korean BBQ, and Georgia Tech Master's Degrees(52:30) Ashish on Writing "AI Security Engineering" and the Rise of AI Agents
Resources spoken about during the interview:
The domain takeover challenge: Detecting and defeating it at scale