Client Side Penetration Testing

Client-Side Vulnerabilities refer to weaknesses or flaws in the web application or website that are primarily exploited on the client side, meaning the user's device (browser, mobile app, etc.). These vulnerabilities are typically tied to the way web browsers interact with web applications, including the execution of scripts, rendering content, or managing user input. Attackers exploit these vulnerabilities to manipulate or gain unauthorized access to data, bypass authentication mechanisms, or alter the behavior of the website or application.

Characteristics of Client-Side Vulnerabilities:

• Executed in the User's Browser: Client-side vulnerabilities depend on how the user's browser interprets or executes code.

• Can Be Exploited by Malicious Users: These vulnerabilities are often exploited by attackers who trick users into executing malicious code, without requiring direct access to the server.

• Impact User Data and Experience: These vulnerabilities can lead to the theft of sensitive information, manipulation of user interfaces, or data corruption.

Common Types of Client-Side Vulnerabilities:

1. Cross-Site Scripting (XSS):

   • Reflected XSS: Malicious scripts are embedded in a URL or query parameter, which is then reflected and executed in the victim's browser.

   • Stored XSS: Malicious scripts are stored on the server (e.g., in a database) and executed in a user's browser when they access a page.

   • DOM-based XSS: The vulnerability arises due to unsafe client-side JavaScript manipulation of the DOM (Document Object Model), which leads to script execution in the victim's browser.

2. Cross-Site Request Forgery (CSRF):

   • Unintended Actions: An attacker tricks a user into making unintended requests (such as transferring money, changing account settings, etc.) while the user is authenticated on a website, leveraging their session cookie.

3. Clickjacking:

   • Hidden Interface: Attackers trick users into clicking on something different from what they think by using transparent or disguised frames on a webpage. This can be used to make users click on invisible buttons, like changing settings or performing other unintended actions.

4. Insecure Direct Object References (IDOR):

   • Manipulating URLs: Attackers modify parameters in a URL to access or manipulate resources they are not authorized to interact with (e.g., viewing someone else’s account).

5. Local Storage & Session Storage Misuse:

   • Sensitive Data Exposure: Some web applications use browser local storage or session storage to store user data. If this data is not properly secured or validated, attackers can access and manipulate it through JavaScript, leading to leakage of sensitive information.

6. Insecure File Uploads:

   • Malicious File Upload: If an application allows file uploads without proper validation, an attacker can upload files containing malicious scripts or executable code, which can be executed in the client’s browser.

7. JavaScript and CSS-based Exploits:

   • JavaScript Manipulation: Attackers may inject malicious JavaScript into a web page, which manipulates the DOM, steals data, or interacts with the backend server without the user's consent.

   • CSS Injection: While less common, CSS-based exploits could manipulate the design of a page to trick users into interacting with hidden or disguised elements.

8. Third-Party Script Vulnerabilities:

   • Exploiting Libraries or Frameworks: If a web application relies on third-party libraries or scripts (e.g., jQuery, Google Analytics, or advertising scripts), vulnerabilities in these libraries can be exploited by attackers to execute malicious code.

9. Weak Client-Side Encryption:

   • Weak Cryptography: Some web applications might attempt to encrypt sensitive data on the client-side (before sending it to the server), but if weak or broken cryptographic algorithms are used, attackers can decrypt the data easily.

10. Man-in-the-Browser (MITB):

    • Malicious Browser Extensions: Attackers use malicious browser extensions or scripts to intercept and modify data being sent between the user’s browser and the server. This allows attackers to perform actions on behalf of the user, steal data, or alter the user's requests.

11. Abusing HTTP Headers:

    • Insecure HTTP Headers: Sometimes the headers (like Referer, Origin, User-Agent) can reveal too much information about the client or user, or they might be used maliciously by attackers to manipulate content or actions.

12. JavaScript Hijacking:

    • Stealing Data via JSON: Attackers hijack JavaScript-based communications (often involving JSON) between the client and server, typically to steal sensitive information or perform unauthorized actions.