Analysis of Exploitation of Stored XSS Vulnerability
/ 4 min read
Quick take - The article analyzes a real-world engagement where a stored Cross-Site Scripting (XSS) vulnerability was exploited, allowing the author to gain administrative access to a web application, while highlighting the importance of cookie protection and the potential consequences of such vulnerabilities despite existing security measures.
Fast Facts
- A stored Cross-Site Scripting (XSS) vulnerability was exploited with customer approval, allowing administrative access to a web application.
- The author faced challenges due to CloudFlare protection but successfully crafted a payload that bypassed these defenses.
- The vulnerability was linked to user comments stored in the database, enabling the author to manipulate the HTML DOM instead of directly stealing cookies.
- XMLHttpRequest (XHR) or AJAX requests were proposed to access the Django Admin page and extract the CSRF nonce token for further exploitation.
- The article highlights the serious implications of XSS vulnerabilities, urging proactive security measures and creative problem-solving.
Exploiting a Stored XSS Vulnerability: A Real-World Engagement
Introduction to Cookie Protection
A recent analysis has shed light on a real-world engagement involving the exploitation of a stored Cross-Site Scripting (XSS) vulnerability. This vulnerability allowed the author to gain administrative access to a web application. The engagement was conducted with formal approval from the customer, ensuring that all activities were authorized.
The article begins by explaining the importance of cookie protection in web applications. Cookies are utilized for user authentication and to differentiate user privileges. Various security measures are associated with cookies to enhance their safe usage, making them a critical component of web security.
The Engagement Process
In the initial phase of the engagement, the author attempted to inject a test XSS payload to assess the application’s frontend for any reflections of the payload. However, CloudFlare protection, implemented by the application administrator, successfully blocked these injected payloads. The author then considered two potential methods to bypass CloudFlare’s defenses:
- Exposing the underlying IP address of the server.
- Crafting a payload that would be accepted by CloudFlare.
Opting for the latter approach, the author developed a dedicated payload after multiple attempts. This payload was successfully reflected back into the HTML Document Object Model (DOM). The payload cleverly utilized a hidden UI element styled with a CSS display none attribute, designed to trigger a callback request to a temporary webhook.
The vulnerability was classified as stored XSS because comments made by users are saved in the application database and displayed when users access the comment section. The author aimed to exploit this vulnerability fully, moving beyond simply verifying the injection point. However, directly stealing the administrator’s cookie was not feasible due to existing security measures.
Strategic Pivot and Consequences
This led to a strategic pivot toward manipulating the HTML DOM instead. Further investigation revealed that the web application was developed using the Django framework, identified by the Wappalyzer Chrome plugin. Attempts to directly access the Django Administration page were unsuccessful, met with unauthorized access messages due to insufficient privileges.
To overcome this challenge, the author proposed sending XMLHttpRequest (XHR) or AJAX requests on behalf of an authenticated user with administrative privileges. This would facilitate access to the content of the Django Admin page and allow the extraction of the Cross-Site Request Forgery (CSRF) nonce token, enabling the author to perform GET and POST requests without violating the same-origin policy.
The author detailed the potential consequences of this exploitation, including the ability to modify, delete, and alter client data, as well as reset personal passwords. The final payload utilized a double JavaScript function call to retrieve the page contents and send the response back to the author’s webhook.
The article emphasizes the significant impact of XSS vulnerabilities, even in applications that employ robust security measures. The author encourages readers to use their creativity and critical thinking in proactively addressing security vulnerabilities.
A disclaimer accompanies the article, clarifying that the material is intended for informational purposes only and should not be interpreted as legal advice.
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