Lion Cipher Lab
Measure what a top-sites allowlist hides in your IOC feed (Tranco + the Public Suffix List)
- Threat Intel Analyst
- Intermediate
- ~75 min
- Free · no account required
Why it matters
Every threat feed leaks benign noise: a CDN hostname that showed up in a sandbox run, a big search engine a malware sample pinged to test connectivity, an ad network. Block those and you break the business; alert on them and analysts drown. So nearly every team adds a shortcut: if an indicator's domain is in a list of the world's most popular sites, throw it away. It works -- and it also throws away phishing pages on free hosting platforms, payloads in cloud storage buckets, and links behind URL shorteners, because all of those live under popular names. The researchers who built the Tranco…
What you'll learn
- Explaining how the Tranco top-sites list is built (several providers, 30-day average, Dowdall rule) and why that makes it steadier than any single source
- Recording a Tranco list ID so an allowlist decision can be reproduced later
- Computing a registrable domain with the Public Suffix List algorithm (longest rule, wildcards, exceptions, the default rule)
- Measuring, on a labeled feed, how many benign indicators an allowlist removes and how many malicious ones it silently hides
- Choosing the right comparison key (exact host, last two labels, PSL-aware registrable domain) and the right IOC types to allowlist at all
- Explaining why a popularity list is a warning, not a verdict, and when a curated MISP warninglist is the better tool
Steps in this lab
- The shortcut you are about to measure
- How Tranco is built -- and why it beats any single list
- Build the three fixtures
- The Public Suffix List: what is the 'registrable domain'?
- Measure three allowlist keys against the labeled feed
- Sweep the threshold: is a smaller N safer?
- A better policy: allowlist registrable domains, never URLs
- Warn, don't delete: the MISP warninglist way
- Pin the list: reproducibility (optional, uses the internet)
- What you actually learned, and the habit to keep