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Introduction:
Broken Access Control consistently ranks as a critical security risk, allowing attackers to bypass authorization and perform actions as privileged users. This deep-dive explores a real-world penetration testing methodology for identifying and exploiting these flaws in web services and APIs, transforming seemingly benign 302 redirects into full-scale system compromise.
Learning Objectives:
- Master advanced filtering techniques with tools like `httpx` and `ffuf` to isolate exploitable endpoints.
- Learn to leverage Burp Suite extensions for automated API endpoint discovery and analysis.
- Understand the process of identifying and validating unauthorized access to backend services.
You Should Know:
1. Asset Discovery and Filtering with Httpx
`cat domains.txt | httpx -sc -title -server -ports 80,443,8080,8443 -o filtered_hosts.txt`
This command takes a list of domains, probes them for HTTP servers on common web ports, and returns the status code, page title, and server banner. The `-sc` flag filters by status code, allowing you to quickly isolate live hosts from a massive list of potential assets, focusing your testing efforts on viable targets.
2. Advanced Directory Fuzzing with Ffuf
`ffuf -w /usr/share/wordlists/dirb/common.txt -u https://TARGET/FUZZ -recursion -recursion-depth 2 -mc 200 -fs 4242`
The initial fuzz often returns numerous 302 redirects. The `-fs` (filter by size) flag is critical here. By excluding responses of a common size (e.g., the size of a login page redirect), you can filter out the noise. The `-mc 200` flag explicitly matches for successful HTTP 200 responses, while `-recursion` automatically fuzzes discovered directories.
3. Analyzing Redirects for Hidden Endpoints
`curl -I https://TARGET/directory`
`curl -L https://TARGET/directory`
When `ffuf` reveals a 302 redirect to a path like /directory, use `curl -I` to fetch the response headers and confirm the redirect. Then, use `curl -L` to follow the redirect automatically. This often unveils hidden API paths or administrative interfaces, such as /directory/v1/endpoint.svc, that are not linked from the main application.
4. Automated WSDL/SOAP Analysis with Burp Suite
Manual steps: After discovering a `.svc` or `?wsdl` endpoint, send the request to Burp’s Repeater. Right-click the request message and select “Send to Wsdler”. The Wsdler extension will automatically parse the Web Services Definition Language (WSDL) file, enumerate all available SOAP operations, and generate formatted requests for each one directly within the Burp UI, ready for testing.
5. Testing for Unauthorized Endpoint Access
`POST /v1/UserService.svc HTTP/1.1`
`Host: target.com`
`Content-Type: text/xml; charset=utf-8`
`Content-Length: length`
`SOAPAction: “http://tempuri.org/GetAllUsers”`
<?xml version="1.0" encoding="utf-8"?> <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <GetAllUsers xmlns="http://tempuri.org/" /> </soap:Body> </soap:Envelope>
Using the requests generated by Wsdler, attempt to execute high-privilege actions like GetAllUsers, CreateUser, or `DeleteAccount` without providing any authentication tokens. A successful 200 response with data confirms a critical Broken Access Control vulnerability, potentially leading to full data exfiltration or system takeover.
6. Windows Command for Service Enumeration (Post-Exploitation)
`sc query type= service state= all | findstr “SERVICE_NAME”`
If an exploited SOAP endpoint allows command injection or remote code execution, this Windows command lists all services. Understanding the system’s services is key for privilege escalation. The `SERVICE_NAME` can then be used with `sc qc “ServiceName”` to query the service’s configuration, including the path to the executable and its permissions.
7. Linux Privilege Escalation Check
`find / -perm -4000 -type f 2>/dev/null`
Once initial access is gained via a web vulnerability, the next step is often privilege escalation. This Linux command searches the entire filesystem for files with the SUID (Set Owner User ID) bit set. These files run with the permissions of their owner, often root. Common examples like find, bash, or `nmap` can be exploited to gain a root shell if they have the SUID bit set.
What Undercode Say:
- Automation is Non-Negotiable: The combination of `ffuf` with smart filtering and Burp extensions like Wsdler turns a days-long manual process into a matter of hours, dramatically increasing testing efficiency and coverage.
- Assume Nothing, Test Everything: A 302 redirect is not a dead end; it’s a clue. The most critical vulnerabilities often lie behind what appears to be a simple redirect or an unlinked path, requiring testers to persistently follow the application’s logic beyond the surface.
The methodology outlined demonstrates a systematic shift from broad reconnaissance to precise exploitation. It underscores that modern Broken Access Control is not just about manipulating parameter IDs but about discovering and interacting with entirely hidden API ecosystems. The critical failure occurs when applications trust the client-side UI as the sole gateway to the backend, leaving unadvertised services completely unprotected. This approach is a blueprint for both red teams to identify these flaws and blue teams to harden their assets against such layered discovery and exploitation techniques.
Prediction:
The automation of API discovery and testing, as demonstrated with Wsdler, will rapidly evolve. We predict a surge in bot-driven attacks that systematically crawl the internet for exposed .svc, graphql, and `swagger.json` endpoints, automatically fuzzing them for Broken Access Control. This will move these attacks from targeted pen-testing scenarios to widespread, opportunistic exploits, forcing a fundamental change in API development where explicit, role-based authorization checks become mandatory for every single endpoint, advertised or not.
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IT/Security Reporter URL:
Reported By: Saud Bin – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
