Find Payment Callback Vulnerabilities

Analyze the mitmproxy dump (log.txt) for payment callback issues for: $ARGUMENTS

Requires: log.txt in the current directory. If it's missing, capture traffic first:
```bash
mitmdump --set flow_detail=3 2>&1 | tee log.txt
```

Vulnerability Types

1. Hash/Signature Not Validated

• Callback accepts any hash value
• Hash parameter present but not verified
• Can change status without valid signature

2. Status Manipulation

• Change status=failed to status=success
• Modify unmappedstatus parameter
• Tamper with transaction result

3. Amount Manipulation

• Modify amount before callback
• Pay less, get full order
• Decimal manipulation

4. Signature Collision

• Same signature works for payment and refund
• Parameter reordering gives same hash
• Missing fields in signature calculation

5. Checksum Generation Exposed

• API returns checksum even on error
• Can generate arbitrary checksums
• Checksum algorithm is weak (MD5/SHA1 without salt)

Testing Approach

# Test callback with modified status
curl -X POST "https://merchant.com/payment/callback" \
  -d "txnid=12345&status=success&hash=original_hash"

# Test with invalid hash
curl -X POST "https://merchant.com/payment/callback" \
  -d "txnid=12345&status=success&hash=aaaa"

Red Flags in Traffic

• Callback URLs with all params in request
• Hash visible in client-side code
• Salt/secret in JavaScript
• Error responses containing valid checksums

Output Format

For each finding:

• Callback URL: Vulnerable endpoint
• Issue: What can be manipulated
• Parameters: Affected fields
• Test: How to exploit
• Impact: Free orders, refunds, etc.
• Fix: Proper server-side validation