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Introduction:
Access control vulnerabilities remain a pervasive threat in web application security, allowing attackers to escalate privileges and access sensitive functionality. This article deconstructs a real-world bug bounty finding where a low-privilege user bypassed authorization checks to access administrative paths, detailing the methodology, tools, and commands used to identify and exploit such flaws.
Learning Objectives:
- Understand the fundamental principles of Broken Access Control and IDOR vulnerabilities.
- Master the use of automated and manual techniques for path enumeration and authorization testing.
- Develop a methodology for systematically testing access controls across web applications.
You Should Know:
- Web Content Crawling with `cewl` and Burp Suite
`cewl https://target.com -w target_paths.txt –auth_type basic –auth_user:user:pass`
This command uses CeWL to spider a target website and generate a custom wordlist of discovered paths. The `–auth_type` and `–auth_user` flags allow it to authenticate as a specific user, ensuring it captures paths visible to that role. To use it, first authenticate as an admin user in your browser, copy the session cookie, and then run the command to build a comprehensive list of endpoints to test.
2. Automated Path Discovery with `gobuster`
`gobuster dir -u https://target.com/admin/ -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -t 50 -c ‘admin_session_cookie=value’`
Gobuster brute-forces directories and files on a web server. The `-c` flag injects a valid admin session cookie, allowing the tool to enumerate paths that are only accessible to authenticated administrators. Run this from the perspective of a high-privilege account to build a target list for subsequent testing with a low-privilege account.
- Session Cookie Manipulation with Browser DevTools & `curl`
`curl -H “Cookie: session=low_priv_cookie_value” https://target.com/admin/user-dashboard > response.html`
This `curl` command tests access to a specific admin endpoint using a low-privilege user’s session cookie. The core testing methodology involves taking paths enumerated as an admin and systematically requesting them with a low-privilege session. Automate this by writing a bash script that iterates through a list of admin paths, sending requests with the low-privilege cookie and checking the HTTP status code for 200 OK responses.
4. Automating Authorization Testing with a Bash Script
!/bin/bash
while read path; do
resp=$(curl -s -o /dev/null -w "%{http_code}" -H "Cookie: session=low_priv_cookie" "https://target.com$path")
if [ "$resp" -eq "200" ]; then
echo "VULNERABLE: $path" >> vuln_paths.txt
fi
done < admin_paths_list.txt
This Bash script automates the testing process. It reads from a file (admin_paths_list.txt) containing paths found by the admin, requests each one with the low-privilege user’s cookie, and logs any paths that return a 200 status code. This is the core automation for identifying Broken Access Control at scale.
5. JavaScript File Analysis with Burp’s JSLinkFinder
`python3 JSLinkFinder.py -i https://target.com -o output.html`
Many modern apps expose API endpoints in client-side JavaScript files. JSLinkFinder parses these files to uncover hidden endpoints and API paths that may not be found by traditional crawlers. Run this against the target, then add the discovered endpoints to your list for authorization testing.
- Windows Access Control Enumeration with `icacls` & `accesschk`
`accesschk.exe -uws “LowPrivUser” “C:\Program Files\SensitiveApp”`
While the original bug was web-based, the principle applies to local systems. Sysinternals `accesschk` checks what access a specific user has to files, directories, and registry keys. This helps identify misconfigured permissions on Windows systems that could allow a low-privilege user to read or write to restricted directories.
7. Linux File Permission Auditing with `find`
`find /opt/webapp/ -type f -perm -o=r -exec ls -la {} \;`
This `find` command locates files within a web application directory that are world-readable (-perm -o=r), meaning any user, including low-privilege ones, can read them. It’s crucial to audit not just web paths but also the underlying file system for improper permissions that could lead to information disclosure.
What Undercode Say:
- Automation is Non-Negotiable: Manual testing for these flaws is inefficient. The key to success lies in automating the enumeration of paths as a high-privilege user and the systematic testing of each path with a low-privilege session.
- The Vulnerability is Often in the Logic, Not the Code: This isn’t a classic coding bug like SQLi; it’s a flaw in the application’s logic and its failure to consistently verify authorization on every endpoint. The mitigation requires a framework-level solution, not just patching a single line of code.
- Scope Expansion is Critical: Don’t limit testing to obvious `/admin` paths. Use JSLinkFinder and deep crawling to discover a vast array of endpoints, including API routes (
/api/v1/admin/) and static resources, as these are frequently overlooked by developers when implementing access checks.
Prediction:
The prevalence of Broken Access Control will intensify with the adoption of more complex, API-driven microservices architectures. As applications decompose into hundreds of discrete services, the attack surface for authorization flaws expands exponentially. We predict a significant rise in automation-driven mass testing for these vulnerabilities, with bug bounty hunters and attackers alike deploying sophisticated scripts to crawl, enumerate, and test thousands of endpoints across a single application in minutes. The future of mitigating these threats lies not in manual code reviews but in the implementation of standardized, centralized authorization middleware that is automatically applied to every endpoint.
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IT/Security Reporter URL:
Reported By: Shivangmauryaa Bounty – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
