performing-subdomain-enumeration-with-subfinder

name	performing-subdomain-enumeration-with-subfinder
description	Enumerate subdomains of target domains using ProjectDiscovery's Subfinder passive reconnaissance tool to map the attack surface during security assessments. Use when working with performing subdomain enumeration with subfinder.
domain	cybersecurity
tags	["subdomain-enumeration","reconnaissance","bug-bounty","attack-surface","subfinder","passive-recon","osint"]
subdomain	web-application-security
version	1.0
author	oyi77
license	Apache-2.0
nist_csf	["PR.PS-01","ID.RA-01","PR.DS-10","DE.CM-01"]

Performing Subdomain Enumeration With Subfinder

Overview

Cybersecurity skill for performing subdomain enumeration with subfinder. Follows industry best practices and security standards.

When to Use

Trigger phrases:

• "performing subdomain enumeration with subfinder"

• "Enumerate subdomains of target domains using ProjectDiscovery's Subfinder passiv"

• During the reconnaissance phase of penetration testing or bug bounty hunting

• When mapping the external attack surface of a target organization

• Before performing vulnerability scanning on discovered subdomains

• When building an asset inventory for continuous security monitoring

• During red team engagements requiring passive information gathering

When NOT to Use

• When you lack proper authorization for testing
• For production systems without change management
• When the task requires legal or compliance expertise beyond technical scope

Prerequisites

• Go 1.21+ installed for building from source
• Subfinder v2 installed (go install -v github.com/projectdiscovery/subfinder/v2/cmd/subfinder@latest)
• API keys configured for passive sources (Shodan, Censys, VirusTotal, SecurityTrails, Chaos)
• Provider configuration file at $HOME/.config/subfinder/provider-config.yaml
• Network access to passive DNS and certificate transparency sources
• httpx or httprobe for validating discovered subdomains

Workflow

# Example: IOC detection
import re

IOC_PATTERNS = {
    "ip": r"\b(?:\d{1,3}\.){3}\d{1,3}\b",
    "domain": r"\b[a-z0-9-]+\.[a-z]{2,}\b",
    "hash_md5": r"\b[a-f0-9]{32}\b",
    "hash_sha256": r"\b[a-f0-9]{64}\b",
}

def extract_iocs(text: str) -> dict:
    return {k: re.findall(v, text)  k, v  IOC_PATTERNS.items()}