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Introduction:
In the critical reconnaissance phase of penetration testing and bug bounty hunting, speed and efficiency in discovering subdomains and live web services can define the success of an engagement. The manual process of enumeration and verification is obsolete, replaced by automated pipelines that deliver actionable intelligence almost instantly. This article deconstructs a powerful one-liner that leverages `rapiddns-cli` and `httpx` to transform a target domain into a list of live hosts with vital HTTP metadata.
Learning Objectives:
- Understand the function and synergy of the `rapiddns-cli` and `httpx` command-line tools in automated reconnaissance.
- Learn how to install, configure, and execute the recon pipeline on both Linux and Windows platforms.
- Master the art of parsing and filtering the output to prioritize targets based on status codes and titles for further testing.
You Should Know:
1. Toolchain Foundation: rapiddns-cli & httpx
The one-liner’s power comes from chaining two specialized tools. `rapiddns-cli` queries RapidDNS, a search engine that aggregates DNS data, to enumerate subdomains. Its output is then piped to httpx, a fast HTTP toolkit that probes each subdomain to identify live web servers and retrieve key response data.
Step-by-step guide:
Installation (Linux/macOS):
Install httpx (Go must be installed) go install -v github.com/projectdiscovery/httpx/cmd/httpx@latest Install rapiddns-cli (Python3 & pip required) pip3 install rapiddns-cli
Installation (Windows – via Git Bash or WSL):
In PowerShell (Admin), install Go, then:
go install -v github.com/projectdiscovery/httpx/cmd/httpx@latest
Add Go bin to PATH: [bash]::SetEnvironmentVariable("Path", "$env:Path;$HOME\go\bin", "User")
pip install rapiddns-cli
Basic Command Execution:
rapiddns-cli search example.com --column subdomain -o text | httpx -silent
This minimal command lists all live subdomains.
2. Decoding the Full Command: Flags and Output
The original command adds crucial flags for intelligence gathering. Let’s break down httpx -silent -sc -title -cl.
– -silent: Suppresses unnecessary output, showing only results.
– -sc: Includes the HTTP status code (e.g., 200, 403, 500).
– -title: Extracts the HTML `
–
-cl: Retrieves the `Content-Length` header.
Step-by-step guide:
Run the full command:
rapiddns-cli search target.com --column subdomain -o text | httpx -silent -sc -title -cl
Sample output:
https://api.target.com [bash] [Internal API Gateway] [bash] https://dev.target.com [bash] [bash] [bash] https://test.target.com [bash] [bash] [bash]
This immediately tells you `api.target.com` is a high-value target, `dev.target.com` may have misconfigured access, and `test.target.com` is erroring.
3. Advanced Filtering and Prioritization
Raw data needs filtering. `httpx` offers filters to narrow down results to the most promising targets, saving time for exploitation.
Step-by-step guide:
- Find specific status codes:
Find only 200 OK responses rapiddns-cli search target.com --column subdomain -o text | httpx -silent -sc -title -cl -status-code 200 Find 403, 401 (potential misconfigurations) rapiddns-cli search target.com --column subdomain -o text | httpx -silent -sc -title -cl -status-code 403,401
- Filter by title or content: Use `-title` in combination with tools like
grep.Find pages with "admin" or "login" in the title rapiddns-cli search target.com --column subdomain -o text | httpx -silent -title | grep -i "admin|login"
4. Integration with Vulnerability Proxies (Bonus)
To actively test the discovered endpoints, pipe the live URLs directly into an active scanning tool like `ffuf` for directory fuzzing.
Step-by-step guide:
Discover live subdomains and fuzz for common directories rapiddns-cli search target.com --column subdomain -o text | httpx -silent | ffuf -u FUZZ -w common_dirs.txt -t 50
This command takes each live subdomain (https://api.target.com`) and appends paths from `common_dirs.txt` (e.g.,/admin,/backup`) to find hidden resources.
5. Building a Recon Script for Automation
For operational efficiency, wrap this logic into a bash script.
Step-by-step guide:
Create a file `recon_scan.sh`:
!/bin/bash
if [ -z "$1" ]; then
echo "Usage: ./recon_scan.sh <domain>"
exit 1
fi
DOMAIN=$1
echo "[] Starting subdomain enumeration for $DOMAIN"
rapiddns-cli search $DOMAIN --column subdomain -o text | httpx -silent -sc -title -cl -o ${DOMAIN}_live.txt
echo "[+] Results saved to ${DOMAIN}_live.txt"
echo "[] Filtering for interesting targets..."
grep -v "[404]|[403]" ${DOMAIN}_live.txt | head -20
Run it: `chmod +x recon_scan.sh && ./recon_scan.sh target.com`.
6. Critical Security and Ethical Considerations
This command chain is for authorized testing only. Unauthorized use against systems you do not own or have explicit permission to test is illegal.
Step-by-step guide for authorized use:
- Obtain Written Authorization: Ensure a signed scope document includes the target domain.
- Rate Limiting: Add `-rate-limit 100` to `httpx` to avoid overwhelming the target’s servers.
httpx -silent -sc -title -cl -rate-limit 100
- Respect
robots.txt: While `httpx` does not automatically respect it, be aware of its directives.
7. Windows PowerShell Adaptation
For testers operating in a native Windows environment, the pipeline can be adapted using PowerShell equivalents.
Step-by-step guide:
Assume you have a text file of subdomains from rapiddns-cli (subs.txt)
$subdomains = Get-Content .\subs.txt
foreach ($sub in $subdomains) {
try {
$resp = Invoke-WebRequest -Uri "https://$sub" -TimeoutSec 5 -ErrorAction SilentlyContinue
Write-Output "$sub [$($resp.StatusCode)] [$($resp.ParsedHtml.title)]"
} catch {
Handle errors (timeouts, 404, etc.)
}
}
While less feature-rich than httpx, this provides a functional native alternative.
What Undercode Say:
- Recon is a Pipeline, Not a Tool: The true power lies in chaining discrete, specialized tools (
rapiddns-clifor DNS, `httpx` for HTTP) to create a seamless intelligence-gathering workflow. This modular approach allows for easy swapping and enhancement of each stage. - Context is King: The raw list of subdomains is noise. The
-sc,-title, and `-cl` flags transform it into signal, providing immediate context (like spotting a “Jenkins” or “phpMyAdmin” title) that allows a tester to prioritize targets within seconds of starting an engagement.
Analysis: This command exemplifies the modern, automated approach to reconnaissance that has become non-negotiable in cybersecurity. It reduces what was once a hours-long manual process to a sub-minute automated task, allowing human researchers to focus on analysis and exploitation. However, it also lowers the barrier to entry for attackers, making robust attack surface management and continuous monitoring imperative for defenders. Tools like this democratize advanced recon, forcing a shift in defense from obscurity to resilience.
Prediction:
The future of reconnaissance lies in even deeper integration of AI and machine learning into these pipelines. We will soon see tools that not only fetch data but also automatically analyze title/content patterns to predict application type, potential vulnerabilities, and default credentials, ranking targets by probable exploitability. Defensively, AI-driven asset discovery and classification platforms will become standard to constantly identify and hardify exposed services that tools like this can find, leading to an automated arms race in the recon phase.
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IT/Security Reporter URL:
Reported By: Omar Aljabr – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅


