An Application Programming Interface (APIs) is a set of protocols and definitions for building and integrating application software. Application Programming Interface (APIs) is a software intermediary and is provided by many organizations to allow the transfer of information between systems, both internally and externally. The functionalities of APIs are used and implemented from basic ticket-booking services, instant messaging applications to highly-complex online banking systems. In 2019, Akamai, one of the leading content delivery networks, reported that 83% of all internet traffic was generated by APIs. APIs power connected our digital world at this age.


API penetration testing is an attempt to evaluate the security of an API implemented by the organization to safely exploit potential and known vulnerabilities in it. It is usually performed using manual or automated technology to systematically compromise the API in various ways to discover any potential vulnerabilities that may be exploited by an attacker. Information gathered about any security vulnerabilities present in the API through penetration testing is documented properly and presented to the relevant team for a quick patch and mitigation. These penetration testing are carried out by either in-house employees or third party security services. Since APIs handle a high volume of sensitive data such as PCI and PII, ensuring their integrity and safety is of the utmost importance through diligent API pentesting.


Due to ease and flexibility it provides, API became the Industry standard for application development, the application development landscape has completely changed because of it .Whether it is Desktop, web or mobile application ,internal or external application, the implementation of API can be seen almost anywhere. Since API is widely used in almost every technology nowadays the attack surface and attack vectors has also increased enormously. API gives access to internal data to the public or allows users to utilize their data.

Vulnerability scan using software and other technology proves to be an efficient way to show what potential security weaknesses are present, but penetration testing can add more context by analyzing if the vulnerabilities could be leveraged to gain access within the organization environment. API penetration testing evaluates the organization’s endpoints, networks and applications from external or internal attempts to circumvent its security controls and gain unauthorized or privileged access to protected assets.


Exploiting APIs is one of the most common attack vectors for data breaches within enterprise applications. API penetration testing can be performed in various different ways depending upon the potential attack types and vulnerabilities types. Mostly the API functions/methods are being tested on how they could be abused and how the authorization and authentication can be bypassed.

There can be several classes of vulnerabilities to test for , some of the most common vulnerabilities listed in Owasp Web Application Security Project (OWASP) Top 10 2019 are as under,

• Broken Object Level Authorization

• Broken User Authentication

• Excessive Data Exposure

• Lack of Resources & Rate Limiting

• Broken Function Level Authorization

• Mass Assignment

• Security Misconfiguration

• Injection

• Improper Assets Management

• Insufficient Logging & Monitoring


A report by Gartner estimates that by 2022, APIs will become one of the most frequent attack vectors. As APIs gained popularity as an ideal way to build applications and expose data and functionalities with permitted third parties, attackers also discover malicious opportunities in targeting APIs. According to Verizon, web application remains a primary target for breaches and APIs now make up 90% of web application attack surface area. A 2020 study by SmartBear found 72% of companies develop both internal and external-facing APIs. These APIs could simply contain hundreds of parameters, and with every new method added, an organization’s potential attack surface grows substantially. Some researchers also believe that APIs pose one of the most serious security threats an organization can face , as APIs provide access to highly sensitive data and functionalities. When API security is not taken into serious consideration, the organization is vulnerable to data breaches which in turn leads to a huge lost in revenue and reputation.


The main goal of API Penetration testing is to take full advantage of the benefits API’s bring while identifying and remediating the substantial risks they impose. API penetration testing also validates an organization’s API that is exposed to the public or third parties are properly secured. API penetration testing helps explore existing weaknesses in an API to reveal real time vulnerabilities and how much impact they can have in a business. To make sure any organization’s business operations are up-and-running all the time and to safeguard the business reputation in the market, the organization’s resources need to be available all the time to the consumers at all cost. Each disruption can have a negative impact on any business. To avoid such chaos , a vulnerability assessment and penetration testing of APIs should be conducted on a regular basis.


We want to discover the security gaps in your API, before an internal or external attacker does. Every API is different, and we are equipped to perform diligent, advanced API penetration testing with API pentesting methodologies tailored to your specific organization requirements. Our team at WALNUT SECURITY SERVICES will go through the API, function by function, to enumerate and analyze ways that an attacker could leverage your vulnerabilities. Our goal is to not only identify and exploit vulnerabilities present in your APIs but help ensure that they are patch by providing a necessary remediation as well.

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