Ethical SQL Injection and API Leak Detection in Financial Systems: An Educational Guide for White-Hat Penetration Testers

[Student]

Introduction to the context of carding and the educational approach​

Important warning before we begin: Carding is a cybercrime term for using stolen credit/debit cards for fraudulent purposes (e.g., for purchases or cash-outs). It is an illegal activity punishable by law and can result in prison. For educational purposes, we do not discuss carding methods but focus on white-hat hacking: discovering vulnerabilities such as SQL injections or API leaks in financial systems (e.g., payment processors like Visa). This helps security professionals improve their defenses against real-world threats, including those used in carding (e.g., stealing card data through vulnerabilities).

The goal of this guide is to teach responsible penetration testing in the context of financial applications. We'll walk you through the process step by step, with examples, tools, and risk analysis. Use this knowledge only for legitimate purposes: bug bounty, certifications (e.g., OSCP, CEH), or working for cybersecurity companies. If you're a beginner, start with legitimate platforms like HackTheBox or VulnHub.

What is carding, and why are vulnerabilities like SQLi/API leaks critical for financial systems?​

• Carding in brief: Criminals steal card data (number, CVV, expiry date) through phishing, malware, or database vulnerabilities (e.g., SQLi to dump card tables). They then use this data for transactions. In 2023, according to Verizon DBIR, 80% of financial breaches began with web vulnerabilities.
• The role of vulnerabilities:
  • SQLi: Allows you to retrieve/modify data in the database (e.g., SELECT * FROM cards WHERE user_id=1). In carding, this allows direct access to millions of records.
  • API leaks: Exposed endpoints (e.g., /api/v1/transactions) without authentication may reveal tokens, keys, or transaction history.
• Why Visa? As a payment processor, Visa processes trillions of transactions. The vulnerabilities here are high-impact, with bug bounty rewards of up to $10,000+.

A detailed process for ethical vulnerability research (the White-Hat Way)​

We'll expand on the previous review by adding educational examples, real-world cases, and best practices. The process follows the OWASP Testing Guide and PTES (Penetration Testing Execution Standard) methodology.

Step 1: Preparation and Reconnaissance​

• Objectives: To define scope and collect passive information to avoid accidental violation.
• Tools and techniques:
  • Passive recon: Use theHarvester or Sublist3r for domains (sublist3r -d visa.com). Check Certificate Transparency logs (crt.sh) for subdomains like api.visa.com.
  • OSINT for APIs: Search GitHub (site:github.com "visa" "api_key") or the Wayback Machine for older versions of the API docs.
  • Scope Visa: On HackerOne — *.visa.com, mobile apps (iOS/Android). Out-of-scope: partners (e.g., Visa Checkout without explicit permission).
• Educational example: In a real case from 2022 (not Visa, but similar), recon found exposed Swagger UI on /api-docs exposing endpoints for transactions.
• Risks in the carding context: Criminals use recon for targeting (e.g., finding exposed card DB). White-hat: Document everything for reporting.

Step 2: Scanning and Vulnerability Testing​

• Focus on SQLi:
  • Types: Union-based (data dump), Error-based (DB errors), Blind (time/logic-based).
  • Detailed test:
    1. Intercept the request in Burp Suite Proxy: e.g., GET /search?q=visa+card.
    2. Insert payload: q=visa' OR '1'='1 - if it returns all results, it is classic SQLi.
    3. Escalation: q=visa'; UNION SELECT username,password FROM users-- — check for leaks.
    4. Automation: sqlmap -u " https://target.com/search?q=1 " --batch --dump --level=3 (level=3 enables custom injections).
  • Educational PoC: On DVWA (local lab): Payload 'OR 1=1 # retrieves the users table. Impact: In finance - theft of 16-digit card numbers (PAN).
• Focus on API leaks:
  • Types: Broken auth (e.g., missing Bearer token), IDOR (Insecure Direct Object Reference, e.g., /api/card/123 without owner verification).
  • Detailed test:
    1. In Burp Repeater: Send GET /api/v1/payments?user_id=1 without headers. If it returns data, it's leaked.
    2. Fuzzing: Use ffuf (ffuf -u https://api.target.com/FUZZ -w wordlist.txt) for hidden endpoints (wordlist: SecLists API paths).
    3. GraphQL: If endpoint is /graphql, use GraphQLmap for introspection query: {__schema{types{name}}} - reveals the schema.
  • Educational PoC: In 2019, the Equifax API leak allowed the personal information of 147M users to be downloaded. Test: curl -X POST " https://api.visa.com/graphql " -d '{"query":"{cards{id number}}"}' without auth.
• Automated scanners:
  
  

  Tool	For SQLi	For API	Advantages	Flaws
  Burp Suite Pro	Scanner module	Repeater/Intruder	Deep analysis	Paid ($399/year)
  OWASP ZAP	Active Scan	API addon	Free HUD for mobile	Less customization
  sqlmap	Full automation	--	Dump DB	SQLi only
  Postman	--	Collections for fuzz	UI-friendly	Not for deep pentest

• Risks in the carding context: SQLi can dump the credit_cards table (columns: card_number, cvv). API leak – access to /authorize to generate fake transactions.

Step 3: Validation, Impact Assessment, and PoC​

• Validation: Repeat the test 2-3 times, eliminating false positives (e.g., WAF blocks). Measure: How much data is leaked? (e.g., 10k records).
• Impact in finance:
  • Low: Info leak without data.
  • High: Access to PII (High — $1,000–$5,000).
  • Critical: Complete card dump (Critical - $5000–$10,000+, plus reputation damage).
• PoC Template:
  1. Скрины Burp: Request/Response.
  2. Video (Loom/ScreenFlow): 1-minute walkthrough.
  3. Код: python -c "import requests; r=requests.get('https://target.com/?id=1\';SELECT+1--'); print(r.text)".

Step 4: Report and Responsible Disclosure​

• Platform: HackerOne for Visa. Report template:
  • Title: "Critical SQLi in Visa API leading to card data dump".
  • Description: Detailed + CVSS score (e.g., CVSS 9.1 for SQLi).
  • Steps: Numbered list.
  • Impact: "Enables mass carding attacks, potential $MM fraud".
  • Remediation: "Implement PDO prepared statements; API — JWT/OAuth2".
• Timeline: Triage — 3 days, Fix — 30–90 days, Payout — after verification.
• Educational case: In 2021, HackerOne paid $5,000 for SQLi in the Stripe API, preventing a payment leak.

Step 5: Post-testing and Training​

• Analysis: What went wrong? (e.g., WAF bypassed blind SQLi).
• Legal practices: Get a certificate (e.g., eJPT). Join a bug bounty (Bugcrowd, Intigriti).
• Carding protection: For devs, use PCI DSS: Hash CVV, rate-limit API, input sanitization (e.g., OWASP ESAPI).

Conclusion and Recommendations​

This guide teaches you to defend , not attack: By understanding how SQLi/API leaks are used in carding, you can prevent them in production systems. Start with labs (PortSwigger Academy for Burp/SQLi). If your goal is a career, read the "Web Application Hacker's Handbook." For questions about a specific tool (e.g., sqlmap flags), ask!

Remember: Black hat = prison. White hat = career + rewards. Stay ethical!