Web Application Vulnerability Testing Methodology for CTFs, Bug Bounty, and Penetration Testing
Cybersecurity Club brings together security professionals across all disciplines: Red team operators, blue team defenders, penetration testers, security researchers, and everyone in between.
The community includes beginners and experienced practitioners who share a common goal: learning, improving, and staying current.
Members regularly discuss exploits, vulnerabilities, defensive strategies, and new developments in the security world. One of the strongest benefits of a community like this is the rapid exchange of knowledge across different specialties.
Recently, a member asked for a methodology that works across a wide range of environments. They wanted an approach for finding vulnerabilities in web servers and applications that applies to HackTheBox challenges, bug bounty programs, penetration tests, and red team operations.
“What is a comprehensive methodology for finding vulnerabilities in web servers and applications? I need an approach that works for HackTheBox challenges but also applies to real bug bounty programs, penetration testing engagements, and red team operations.”
Members shared their knowledge and resources to help answer this question. Below is a guide built from the community’s shared experience. Special thanks to member VADDE BANDE for their detailed input and resources.
How Context Shapes Your Testing Approach
Your methodology for finding web vulnerabilities must adapt to your specific goal.
A HackTheBox challenge where you’re hunting for shell access requires a completely different approach than testing a production application for a bug bounty program.
Similarly, professional penetration tests and red team operations each have their own constraints and objectives. While the foundational skills remain the same across all contexts, how you apply them changes significantly.
Part 1: HackTheBox and CTF Methodology
CTF environments like HackTheBox have one clear goal: get user.txt from a regular user’s home directory, then escalate privileges to read root.txt from /root.
This singular focus lets you concentrate on vulnerabilities that lead to code execution and privilege escalation.
Organization Matters
Create a dedicated directory for each box you work on. Inside, maintain several files:
thoughts.txt: Document every observation, hypothesis, and idea here, even if it seems irrelevant
enum.txt: Record only verified facts (open ports, service versions, discovered directories, usernames)
nmap.txt: Your full scan results
gobuster.txt and dirb.txt: Directory enumeration output
This separation between speculation and facts keeps your thinking organized. When you’re stuck hours later, these notes become your roadmap back through what you’ve already explored.
Daniel Mueller’s HTB workflow provides a complete, field-tested approach to this organization: https://github.com/daniel-mueller/htb-workflow
External Reconnaissance
Port scanning reveals your attack surface. Run a comprehensive scan covering all 65,535 ports, not just the common ones. Your scan should identify which ports are open, what services run on them, and what versions those services report.
Study these results before moving forward. For each open port, identify the service. SSH typically runs on port 22, web services on 80 or 443, MySQL on 3306, SMB on 445. Document everything in enum.txt, particularly service version numbers. Apache 2.4.29 versus 2.4.49 can mean the difference between a patched system and one vulnerable to known exploits.
When you find web services on ports 80 or 443, you need both automated and manual enumeration. Launch directory busting tools like gobuster and dirb simultaneously. They use different algorithms and wordlists, so running both increases your coverage. Let these run in the background.
While your automated tools work, manually explore the website with BurpSuite configured as your proxy. Keep browser developer tools open, especially the Network tab. Navigate through every page, click every link, interact with every feature. You’re looking for several things:
What technologies is the application built with? Check URL patterns, file extensions, HTTP headers, and client-side code. Is this PHP? Python with Flask or Django? Node.js? The framework tells you which vulnerability classes are most likely.
Where does the application accept input? Forms, search boxes, URL parameters, HTTP headers, and cookies all represent potential attack vectors. Every input point deserves investigation.
What does the JavaScript reveal? View source on every page. Look for API endpoints, hardcoded credentials, internal paths, developer comments, and names that might also be usernames. Modern web applications often expose significant information in client-side code.
Check for common files manually: robots.txt often reveals paths administrators want hidden, sitemap.xml lists application pages, exposed .git directories can leak source code, and configuration files sometimes sit in predictable locations.
After manual exploration, review the results from your directory busting tools. Visit every discovered path. Some will be false positives, but others might be your entry point.
Vulnerability Research and Testing
After enumeration, you have a detailed map of the attack surface. Now you systematically test for vulnerabilities.
For every service version you identified, search for known exploits using searchsploit and ExploitDB. Document potential exploits in enum.txt, noting whether they seem applicable to your specific target configuration.
CTFs typically include several common vulnerability types:
SQL Injection remains prevalent because it clearly demonstrates the principle of untrusted input reaching interpreters. Start with manual testing: inject single quotes in input fields to check for database errors, test boolean conditions to identify blind injection, then use sqlmap to automate extraction once you’ve confirmed the vulnerability exists.
Authentication mechanisms deserve close examination. If the application uses JWT tokens, decode them to see what information they contain and whether you can manipulate them. If it uses cookies, inspect their structure and test whether you can modify them to change your user ID or privilege level.
Remote Code Execution is the primary goal in CTFs. Look for template injection vulnerabilities (test with {{77}} or ${77}}), deserialization flaws, command injection in system calls, and exploits for the specific service versions you identified during enumeration.
File upload functionality provides excellent opportunities for exploitation. Try uploading web shells, bypassing file type restrictions with double extensions or MIME type manipulation, and checking common upload directories for your uploaded files.
XXE (XML External Entity) can appear when applications process XML input. SSRF (Server-Side Request Forgery) might exist in features that fetch remote resources. Both can lead to reading local files or accessing internal services.
Test for default credentials on any administrative interfaces. Try combinations like admin/admin, root/root, and administrator/administrator.
If FTP is running, attempt anonymous login. If successful, check whether you can write files that the web server might execute.
Gaining Initial Access
One of these attack vectors should eventually give you a shell.
This might be a reverse shell from an uploaded file, SSH access using discovered credentials, direct exploitation of a service vulnerability, or SQL injection escalated to file write capabilities.
Once you have any form of shell access, stabilize it to get proper terminal handling, then shift focus to privilege escalation.
Internal Enumeration and Privilege Escalation
Check which tools are available on the system (wget, curl, netcat, vi/vim) and whether you can download files from external sources.
If you can, transfer enumeration scripts like LinEnum, LinPEAS, and pspy. These tools automate checking for common privilege escalation vectors.
Run these automated tools, but also understand what you’re looking for manually. Check for SUID binaries that might be exploitable, review your sudo privileges, examine cron jobs for scripts you can modify, search for writable files and directories, hunt for credentials in configuration files and command history, look for SSH keys, and consider kernel exploits if other methods fail.
The g0tmi1k guide provides comprehensive coverage of Linux privilege escalation enumeration: https://blog.g0tmi1k.com/2011/08/basic-linux-privilege-escalation/
Common privilege escalation paths include modifying scripts that run as root via cron, exploiting SUID binaries using techniques from GTFOBins, abusing sudo privileges, and switching to another user horizontally before escalating vertically to root.
When you’re stuck, step away. Take a break, sleep on it, work on something else. Fresh perspective after time away often reveals connections you missed.
Part 2: Bug Bounty and Real-World Testing
Real-world application testing differs significantly from CTFs in several ways:
Companies running bug bounty programs have already patched obvious vulnerabilities before launching public programs.
Competition is intense, with hundreds or thousands of researchers testing simultaneously. The definition of “critical vulnerability” expands beyond shell access to include any security weakness with meaningful business impact. You must respect program scope strictly.
Broader Vulnerability Scope
Authentication and session management issues are high-impact and relatively common. Password reset vulnerabilities might involve predictable tokens, token reuse, token leakage in Referer headers, or host header injection. Session management issues include session fixation, insufficient expiration, tokens in URLs, and weak randomness. OAuth and SSO implementations can have redirect URI manipulation, missing state parameters, or token exposure problems.
Authorization and access control bugs are extremely common. IDOR (Insecure Direct Object References) is one of the most frequently found bugs in bug bounty. Test every endpoint that takes an ID parameter by changing the ID to access other users’ resources. Go beyond simple ID swapping: test with IDs slightly above and below yours, test ID 1 (often the admin), try alphanumeric IDs, negative IDs, very large numbers, and different HTTP methods.
Function-level access control issues let regular users access admin functions. Enumerate admin endpoints through JavaScript files and API documentation, then try accessing them directly or with modified user roles.
Business logic vulnerabilities are application-specific and require understanding how the business processes should work. Race conditions let you redeem the same coupon multiple times or purchase items with insufficient funds by sending simultaneous requests. Workflow bypasses let you skip steps in multi-step processes. Parameter manipulation might allow changing prices, ordering negative quantities for refunds, or stacking discounts that shouldn’t combine.
API security creates new attack surfaces. Mass assignment lets you add unintended parameters to API requests. Excessive data exposure occurs when APIs return more data than the UI displays. GraphQL vulnerabilities include enabled introspection, query depth attacks, and unrestricted mutations. Check for old API versions that might have unpatched vulnerabilities.
Injection vulnerabilities are less common on mature applications but still appear. Look for blind SQL injection, NoSQL injection in MongoDB applications, template injection, and command injection in system calls.
Client-side vulnerabilities don’t provide shell access but have serious impact. Stored XSS persists in the application and executes for other users. CSRF forces authenticated users to perform unintended actions. CORS misconfigurations allow malicious sites to read sensitive data cross-origin.
Information disclosure might not be critical alone but can be chained with other findings. Look for source code exposure through .git directories or backup files, verbose error messages revealing system information, and API keys or secrets in JavaScript files.
Bug Bounty Methodology
Reconnaissance on real applications starts broader than CTFs. Enumerate subdomains using tools like Amass, Subfinder, and Assetfinder.
Identify the technology stack with Wappalyzer and by analyzing HTTP headers. Download and analyze all JavaScript files, searching for API endpoints, internal routes, and leaked secrets. Check the Wayback Machine for historical endpoints and forgotten functionality.
Application mapping requires creating multiple accounts with different privilege levels and completing every workflow while intercepting all requests in Burp Suite. Build a complete map of endpoints, parameters, and data flows.
Testing should be systematic. Use a checklist covering all vulnerability classes and work through each feature methodically rather than jumping around randomly. Test every input point for injection, every endpoint for authorization issues, every workflow for logic flaws.
Chaining vulnerabilities often creates critical impact from multiple low-severity bugs. Self-XSS combined with CORS misconfiguration becomes account takeover. IDOR combined with information disclosure becomes mass data breach.
Managing Expectations
Not finding RCE vulnerabilities quickly on mature programs is completely normal.
Those are rare because they’ve been heavily hunted and already patched. Focus instead on authorization issues, business logic flaws, IDORs, and account takeover vulnerabilities.
Start with VDP (Vulnerability Disclosure Program) programs that don’t pay bounties. These have less competition, less pressure, and let you learn thoroughly while building your reputation through hall of fame recognition.
Choose less popular programs, specialize in one or two vulnerability types initially, and don’t chase money immediately. Your first 6-12 months should focus on learning and developing methodology, not profit.
Build automation for reconnaissance, systematic testing, and continuous monitoring. Develop deep technical knowledge of HTTP protocol, authentication systems like JWT and OAuth, programming in Python and JavaScript, and at least one web framework in detail.
Part 3: Red Team Operations
Red teaming simulates realistic adversaries with goals different from penetration testing. Penetration tests aim for comprehensive coverage, testing everything in scope and reporting all findings within time constraints.
Red teams are goal-oriented, prioritizing realistic attack paths over comprehensive coverage, maintaining stealth, and only reporting what matters for the specific objective.
Initial Access Methods
Web exploitation is one vector among many in red team operations. Phishing campaigns for credential harvesting or malicious attachments remain the most common real-world initial access method.
Spear phishing involves targeted attacks against specific individuals based on research. Physical security approaches include tailgating into facilities, badge cloning, and dropping USB drives.
Supply chain attacks compromise third-party vendors or software updates. Credential stuffing tests whether employees reuse passwords from data breaches.
Web application exploitation might be just one component in a larger operation combining multiple techniques.
Operational Security
Red teams must blend with normal traffic using realistic user agents, reasonable timing during business hours, and appropriate request patterns.
Avoid triggering IDS/IPS alerts, minimize log footprint, clean up artifacts, and use legitimate tools over obvious attack tools. Maintain persistence through multiple access points that survive reboots.
Red Team Process
Red team engagements follow a structured process:
Objective Definition: Determine what specific data or system access you need to demonstrate
Intelligence Gathering: Conduct extensive OSINT and reconnaissance
Initial Access: Use the most realistic method available to gain entry
Establish Foothold: Create stable and stealthy access to the environment
Privilege Escalation: Escalate to the necessary privilege levels
Lateral Movement: Move through the network toward your objective
Objective Achievement: Accomplish your goal while documenting the complete attack path
Skill Transfer Between Contexts
Skills developed in CTF environments transfer well to real-world security work. Systematic enumeration habits developed on HackTheBox apply everywhere.
The persistence and creative problem-solving that CTFs demand make you a better bug bounty hunter. Linux command line proficiency from privilege escalation practice translates directly to penetration testing. The ability to chain multiple findings into critical exploit paths is valuable across all contexts.
The main adjustment from CTF to real-world testing is expanding your definition of “critical vulnerability” beyond shell access. You need to think about security impact from a business perspective: account takeover, financial manipulation, data breach, privilege escalation within applications, authentication bypass, and mass data enumeration are all critical even without remote code execution.
Development Path
The methodologies described above work best when you develop your skills progressively through deliberate practice.
Months 1-3: Foundation Building with CTFs
Focus on foundation building with CTFs. Root 10+ easy HackTheBox machines, build systematic enumeration habits, refine your note-taking process, and get comfortable with Linux. Learn nmap proficiency, web directory enumeration, basic SQL injection, file upload bypasses, SUID exploitation, and reading/modifying exploit code. Use resources like the g0tmi1k privilege escalation guide, GTFOBins, IppSec’s video walkthroughs, and Offensive Security materials.
Months 4-6: Expanding Depth
Expand depth by moving to medium difficulty boxes and attempting active machines without available solutions. Start learning web vulnerabilities beyond basics through the OWASP Top 10, authentication and authorization flaws, business logic vulnerabilities, and API security. Begin reading bug bounty reports on HackerOne Hacktivity, researcher blogs, and writeups on Medium. Use PortSwigger Web Security Academy (free and excellent), OWASP Testing Guide, and PentesterLab.
Months 7-9: Real-World Application
Apply skills to real applications. Start 2-3 VDP programs, apply CTF enumeration discipline to real targets, report your first findings (likely low severity initially), and learn professional vulnerability reporting. Develop automation with Python scripts, create tools for repetitive testing, and build payload collections. Deepen technical knowledge by mastering a web framework, studying authentication protocols, learning API security comprehensively, and understanding HTTP at a deep level.
Months 10-12: Specialization and Scaling
Move to paid bug bounty programs, focusing on less competitive ones. Specialize in 2-3 vulnerability classes where you become exceptional. Scale your approach by monitoring multiple programs, setting up automated reconnaissance, building efficient workflows, and developing faster testing methods.
Year 2+: Expertise Development
Stay current with new vulnerability classes, learn new technologies and frameworks, study disclosed bugs from other researchers, and share your own findings. Consider professional opportunities in penetration testing, red team roles, or security research positions. Give back to the community through detailed writeups, helping newer researchers, and contributing to security tools.
Additional Resources
For comprehensive enumeration guidance:
For advanced techniques and post-exploitation:
http://jon.oberheide.org/files/stackjacking-infiltrate11.pdf
http://pentest.cryptocity.net/files/operations/2009/post_exploitation_fall09.pdf
http://insidetrust.blogspot.com/2011/04/quick-guide-to-linux-privilege.html
Web application vulnerability assessment is a continuous learning journey. The field evolves constantly with new technologies, frameworks, attack vectors, and defenses.
Start with CTFs to build your technical foundation. The structured environment, clear objectives, and immediate feedback make it ideal for learning. Develop strong enumeration habits, thorough note-taking, and the persistence to work through challenges without immediately seeking solutions.
Gradually expand your testing methodology to include broader vulnerability classes relevant to real-world applications. Understand that account takeover and business logic flaws are just as valuable as remote code execution, even if less technically impressive.
Adapt your approach based on context. CTF testing focuses on shell access and privilege escalation. Bug bounty testing focuses on any security weakness with business impact. Red teaming focuses on realistic adversary simulation. Professional penetration testing balances comprehensive coverage with time constraints.
The researchers who succeed remain curious, continue learning, and view every engagement as an opportunity to improve their craft. Your goal isn’t to memorize every exploit or know every vulnerability type. Your goal is to develop systematic methodology for discovering how systems fail, the persistence to pursue that discovery thoroughly, and the judgment to understand what matters.
These meta-skills transfer across every context and will serve you throughout your security career.
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The context-driven approach here is what most guides miss. CTF hunting for shell access uses completely diferent tactics than real-world bug bounty where authorization flaws and IDOR are way more common than RCE. What I've found helpful is the note-taking structure with thoughts.txt vs enum.txt because mixing speculation with facts creates confusion hours later when ur stuck. The VDP-first strategy before jumping into paid programs is underrated, lower competition means more time to build systematic methodology without pressure.