Many companies believe that implementing a WAF resolves a significant portion of application security issues.
The logic seems straightforward. If there is a layer filtering malicious requests, attacks like SQL Injection, XSS, or parameter manipulation should be automatically blocked.
In practice, the scenario is quite different.
WAFs primarily operate using rules and signatures of known attacks. They are effective against trivial attacks but can fail when an attacker alters the request format, uses different encoding, or exploits specific application behaviors.
This is precisely where a real pentest starts to make a difference.
What Bypassing a WAF Really Means
When we talk about bypassing a WAF, we are not necessarily referring to exploiting a flaw in the application firewall itself.
Most of the time, the bypass occurs because the WAF and the application interpret the request differently.
The WAF may analyze a request and deem it safe, while the backend interprets that same content in another way.
This difference in interpretation creates opportunities for attacks to slip through the protection layer.
During real pentests, it is common to encounter situations such as:
- parsing differences between layers
- multiple encoding formats
- parameters manipulated in different parts of the request
- specific application behaviors
Exploiting these differences requires contextual analysis of the system. Automated tools rarely manage to do this in depth.
Common Techniques Used to Bypass Protections
During pentests, certain techniques frequently emerge when the goal is to circumvent protection mechanisms like WAFs.
One of them is the use of alternative encoding. Many WAFs analyze payloads assuming a specific format, but the application may decode the input differently.
A classic payload might be blocked:
GET /product?id=1' OR '1'='1But small changes in encoding can allow it to pass through the filter:
GET /product?id=1%27%20OR%20%271%27=%271Another common technique is payload fragmentation. Instead of sending the complete attack in a single parameter, it can be split into parts of the request.
GET /search?q=' OR 1 HTTP/1.1
Cookie: session=abc; part=1=1--To the WAF, it may appear as just divided text. To the backend, this could end up being interpreted as a single payload.
It is also common to exploit differences between HTTP methods. Some protection rules are stricter for GET requests than for other methods.
GET /api/login?user=admin&pass=' OR '1'='1While the same payload may pass when sent using another method:
POST /api/login
Content-Type: application/json
{"user":"admin","pass":"' OR '1'='1"}Another interesting vector involves less monitored headers that some applications use internally.
GET /profile HTTP/1.1
X-Original-URL: /adminDepending on the architecture, this header may change the path interpreted by the backend, allowing access to resources that would normally be protected.
These examples highlight an important point: bypassing a WAF rarely relies on a single technique. It typically involves understanding how different layers of the application interpret the request.
Where Scanners Typically Fail
Security tools are very effective at identifying known patterns.
They can quickly find insecure configurations, vulnerable endpoints, and already cataloged flaws.
The problem is that bypassing protection rarely follows a fixed pattern.
It depends on factors such as:
- application behavior
- business logic
- parameter parsing
- internal integrations
- interpretation differences between layers
A real pentest involves observing these behaviors, testing hypotheses, and adapting attacks as the system reacts. It is an activity that requires offensive reasoning.
Pentest AI-First
To speed up the initial phase of testing, HackerSec employs a methodology called Pentest AI-First.
In this model, an artificial intelligence agent quickly executes tasks such as technical reconnaissance, endpoint enumeration, and initial exploitation testing, allowing for much faster mapping of attack surfaces.
HackerSec applies this methodology using a proprietary AI agent called Yaga, developed specifically to support offensive cybersecurity operations.
Yaga executes the first offensive layer of the process, while HackerSec specialists deepen the attacks by exploring more complex scenarios, such as bypassing protections, exploiting business logic, and chaining vulnerabilities.
This model combines the operational speed of artificial intelligence with human offensive reasoning, enhancing the real capability of the pentest.
Why WAFs Don’t Replace Pentests
WAFs remain an important layer of protection and help block trivial attacks. However, relying solely on defense solutions creates a false sense of security.
In various pentests conducted by HackerSec, we found applications protected by commercial WAFs that were still exploitable through request manipulation, vulnerability chaining, or business logic exploitation.
This happens because defensive mechanisms are designed to block known patterns. Real attacks often exploit application behavior and interpretation differences between layers, something that is rarely covered by protection rules alone.
Nowadays, it is not enough to blindly trust defensive solutions. The most effective way to understand the real security level of an application is to test it offensively and continuously, simulating the behavior of a real attacker.
Continuous Offensive Cybersecurity
Applications are constantly evolving, new features are added, and integrations expand the attack surface. Therefore, security cannot be treated as a one-time check.
HackerSec is a leader in offensive cybersecurity and serves large companies by offering a platform for continuous offensive testing. On the platform, clients can request pentests whenever necessary, continuously, and all tests are conducted by real specialists. Each reported vulnerability undergoes rigorous technical validation, ensuring that only real flaws are reported.
To learn more about the platform and understand how this continuous offensive cybersecurity approach works, visit https://hackersec.com/.