Cross-Origin Resource Sharing (CORS) Misconfiguration

Executive Summary:

This report addresses a significant security vulnerability known as Cross-Origin Resource Sharing (CORS) Misconfiguration within our application. CORS Misconfiguration occurs when web servers are improperly configured to allow cross-origin requests from unauthorized domains, potentially leading to security risks such as data leakage, unauthorized access, or cross-site request forgery (CSRF) attacks. This report aims to detail the vulnerability, its potential impact on our systems and users, and actionable recommendations for mitigation.

Description of the Vulnerability:

CORS Misconfiguration vulnerabilities arise when web servers incorrectly specify Access-Control-Allow-Origin headers, allowing cross-origin requests from domains that should not have access to sensitive resources or APIs. Attackers can exploit these misconfigurations to perform unauthorized cross-origin requests, access sensitive data, or execute actions on behalf of authenticated users. Common examples include allowing wildcard origins (*) or specifying overly permissive Access-Control-Allow-Origin headers.


The impact of CORS Misconfiguration vulnerabilities can vary depending on the sensitivity of exposed resources or APIs and the attacker's capabilities. Attackers can exploit these vulnerabilities to steal sensitive data, perform unauthorized actions, or launch CSRF attacks against authenticated users, potentially leading to financial loss, reputational damage, or legal consequences for our organization.


The likelihood of exploitation depends on various factors including the visibility of exposed resources or APIs, the complexity of CORS configuration, and the attacker's knowledge and motivation. However, given the widespread adoption of web APIs and the potential impact of unauthorized cross-origin requests, the risk associated with CORS Misconfiguration vulnerabilities is significant if not properly mitigated.

Steps to Reproduce:

  1. Identify web resources or APIs within the application that are accessible via cross-origin requests.
  2. Use a web browser or automated tools to send cross-origin requests from unauthorized domains to the identified resources or APIs.
  3. Analyze the application's response and observe if cross-origin requests are allowed or blocked based on CORS configuration.
  4. Determine if unauthorized access or data leakage occurs as a result of improperly configured CORS headers.

Recommendations for Developers:

  1. Implement Proper CORS Configuration: Configure web servers to specify appropriate Access-Control-Allow-Origin headers, limiting cross-origin requests to trusted domains only.
  2. Use CORS Pre-flight Requests: Implement CORS pre-flight requests (OPTIONS) to verify the origin and method of cross-origin requests before allowing access to sensitive resources or APIs.


Addressing CORS Misconfiguration vulnerabilities is critical to protecting against unauthorized access, data leakage, and CSRF attacks within our application. By implementing proper CORS configuration and using pre-flight requests, we can mitigate the risks associated with CORS Misconfiguration vulnerabilities and enhance the overall security posture of our systems.