Content Sniffing Template

Executive Summary:

This report addresses a significant security vulnerability known as Content Sniffing within our application. Content Sniffing, also known as MIME sniffing, occurs when web browsers interpret the content type of a resource based on its content rather than the declared MIME type, potentially leading to security risks such as cross-site scripting (XSS) attacks, data leakage, or content spoofing. This report aims to detail the vulnerability, its potential impact on our systems and users, and actionable recommendations for mitigation.

Description of the Vulnerability:

Content Sniffing vulnerabilities arise when web browsers override the declared MIME type of a resource and attempt to determine the content type based on its actual content. Attackers can exploit this behavior by manipulating the content of a resource to trick the browser into interpreting it as a different content type, potentially leading to security vulnerabilities such as XSS attacks or data leakage. Common examples include serving HTML content with a declared MIME type of image/png to bypass XSS protections or serving executable content with a declared MIME type of text/plain to evade download warnings.


The impact of Content Sniffing vulnerabilities can be significant, leading to various security risks including XSS attacks, data leakage, or content spoofing within our application. Attackers can exploit Content Sniffing to bypass security controls, execute malicious scripts in the context of our web pages, or manipulate the presentation of content to deceive users or steal sensitive information. The consequences may include compromised user accounts, data breaches, or reputational damage to our organization.


The likelihood of exploitation depends on various factors including the visibility of resources served by our application, the behavior of web browsers regarding MIME type interpretation, and the attacker's knowledge and motivation. However, given the prevalence of Content Sniffing vulnerabilities in web applications and the potential impact on security controls and user trust, the risk associated with this vulnerability is significant if not properly mitigated.

Steps to Reproduce:

  1. Identify resources within our application that serve content with declared MIME types.
  2. Manipulate the content of these resources to trick web browsers into interpreting them as different content types.
  3. Serve the manipulated resources to web browsers and observe if they are interpreted incorrectly based on their actual content.
  4. Determine if security controls such as XSS protections are bypassed or if sensitive information is leaked due to incorrect MIME type interpretation.

Recommendations for Developers:

  1. Implement Strict MIME Type Enforcement: Configure web servers to send the X-Content-Type-Options: nosniff header to instruct web browsers to adhere strictly to declared MIME types, mitigating the risk of Content Sniffing vulnerabilities.
  2. Use Secure Content Delivery: Serve content with appropriate declared MIME types and ensure that it is free from malicious content or manipulations that could lead to incorrect interpretation by web browsers.


Addressing Content Sniffing vulnerabilities is critical to protecting against XSS attacks, data leakage, and content spoofing within our application. By implementing strict MIME type enforcement and using secure content delivery practices, we can mitigate the risks associated with Content Sniffing and enhance the overall security posture of our systems.