API Pentesting: Evasion & Combining Techniques
Summary
Today I learned that finding a vulnerability is rarely the end of the story.
Real-world impact usually comes from:
- Bypassing security controls
- Combining multiple weaknesses together
This mindset is what separates basic vulnerability discovery from real API exploitation.
Evasion Techniques
Many APIs rely on protections such as:
- WAFs
- Rate limiting
- Input validation rules
These controls often detect patterns, not intent.
By slightly modifying payloads, it is sometimes possible to bypass them.
Common Evasion Methods
Techniques I practiced include:
- URL encoding and double encoding
- Case switching in endpoints and parameters
- Adding string terminators and special characters
- Manipulating headers and request structure
The goal is not to break functionality, but to avoid detection logic.
Combining Vulnerabilities
Low-severity issues often become critical when chained together.
Examples of effective combinations:
- BOLA + BFLA → full privilege escalation
- Improper Assets Management + Brute Force → account takeover
- Excessive Data Exposure + Authentication flaws
- Mass Assignment + Business Logic abuse
Each individual issue may seem limited, but together they create real risk.
Practical Mindset Shift
Instead of stopping at:
“This endpoint is vulnerable”
I learned to ask:
- What else can interact with this?
- Can this bypass an existing control?
- Can this increase impact?
- Can this be automated?
This approach turns isolated bugs into attack chains.
Tooling Support
Tools like Burp Suite and WFuzz help automate evasion and chaining by supporting:
- Multiple encoders
- Payload transformations
- Prefixes and suffixes
- Large-scale request testing
Automation makes bypass techniques repeatable and reliable.
Security Impact
When evasion and chaining are successful, the result is often:
- Full account compromise
- Authorization bypass
- Business logic abuse
- Large-scale data exposure
Security controls that are not tested against evasion techniques provide a false sense of safety.
Key Takeaway
Never stop at the first vulnerability.
Real API exploitation comes from:
- Thinking beyond single issues
- Understanding how controls fail
- Combining weaknesses strategically
This mindset is essential for effective API pentesting.