Certificate Transparency (CT) Logs – The Watchdogs of Web Trust#

Core Idea:

Certificate Transparency Logs are public records of all SSL/TLS certificates issued by Certificate Authorities (CAs). Their goal is to make certificate issuance transparent and detect rogue or mis-issued certificates early.

Why it matters in security recon:

• Helps detect unauthorized subdomains and rogue certificates.
• Exposes old or expired certs, which may lead to vulnerable or forgotten infrastructure.
• Acts as a source for subdomain enumeration—no brute-forcing required.

Tools:

• crt.sh – easy to use, good for quick checks.
• Censys – powerful for deep analysis and linking certs to hosts.

Automation Example (with curl & jq):

curl -s "https://crt.sh/?q=facebook.com&output=json" \
| jq -r '.[] | select(.name_value | contains("dev")) | .name_value' \
| sort -u

Crawling – Mapping the Web, One Link at a Time#

Core Idea:

Crawling is like casting a web across the internet. Crawlers visit a page, extract links, then visit those links, and repeat the process.

Two main crawling strategies:

• Breadth-First Crawling (BFS) – good for full coverage.
• Depth-First Crawling (DFS) – useful for digging deep quickly.

Valuable Data Extracted:

• Links – find hidden or internal pages.
• Comments – users might leak useful info.
• Metadata – titles, descriptions, versions.
• Sensitive Files – backups, config files, logs.

Context is Key:

A single comment or exposed file might seem unimportant—but when cross-referenced with other data points (e.g. an accessible /files/ directory or metadata showing outdated versions), it can reveal real vulnerabilities.

Think like a detective: each piece of data is a clue, and together, they form a story.

TL;DR – Recon Power Combo#

• Use CT Logs to uncover subdomains, certificate abuse, and legacy assets.
• Use Crawlers to extract site architecture, sensitive files, and insights from context.