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Subdomains are an essential part of web infrastructure, often revealing hidden services, development environments, or vulnerable endpoints. Security professionals and ethical hackers frequently use subdomain enumeration to expand their attack surface during penetration testing. One efficient way to discover subdomains is by leveraging RapidDNS, a free online service that aggregates DNS data.
How to Use RapidDNS for Subdomain Enumeration
The following Bash function automates subdomain discovery using `curl` and grep:
rapiddns(){ curl -s "https://rapiddns.io/subdomain/$1?full=1" \
| grep -oP '_blank">\K[^<]*' \
| grep -v http \
| sort -u }
**Usage:**
rapiddns target.com
### **You Should Know:**
1. **Alternative Tools for Subdomain Enumeration**
- Sublist3r:
sublist3r -d target.com
- Amass:
amass enum -d target.com
- Assetfinder:
assetfinder --subs-only target.com
2. **Validating Discovered Subdomains**
Use `httprobe` to check live hosts:
cat subdomains.txt | httprobe
3. **DNS Recon with Dig**
Query DNS records for additional insights:
dig A target.com dig MX target.com
4. **Automating with Bash**
Combine multiple tools for deeper reconnaissance:
subdomains=$(rapiddns target.com) echo "$subdomains" | httprobe > live_subdomains.txt
5. **Windows Equivalent (PowerShell)**
Invoke-WebRequest -Uri "https://rapiddns.io/subdomain/target.com?full=1" | Select-String -Pattern "_blank"">([^<]+)"
### **What Undercode Say**
Subdomain enumeration is a critical step in reconnaissance, helping identify overlooked entry points. Combining automated tools like RapidDNS, Sublist3r, and manual verification ensures comprehensive coverage. Always validate findings to avoid false positives and integrate results into broader security assessments.
### **Expected Output:**
[/bash]
api.target.com
dev.target.com
mail.target.com
[bash]
Relevant URLs:
– RapidDNS
– Sublist3r GitHub
– Amass GitHub
References:
Reported By: Zlatanh Find – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
