Subdomain Takeover Template

Executive Summary:

This report addresses a critical security vulnerability known as Subdomain Takeover within our application. Subdomain Takeover occurs when an attacker gains control over a subdomain that was previously pointing to an external service or resource, allowing them to host malicious content, conduct phishing attacks, or compromise user sessions. This report aims to detail the vulnerability, its potential impact on our systems and users, and actionable recommendations for mitigation.

Description of the Vulnerability:

Subdomain Takeover vulnerabilities arise when a subdomain that was previously pointed to an external service, such as a cloud hosting provider, CDN, or third-party service, becomes unclaimed or misconfigured, allowing attackers to register or point the subdomain to malicious content. Attackers can exploit these vulnerabilities to host phishing pages, distribute malware, or steal user credentials, potentially compromising the security and integrity of the application. Common examples include unclaimed subdomains pointing to expired AWS S3 buckets or unconfigured subdomains pointing to inactive services.


The impact of Subdomain Takeover vulnerabilities can be severe, leading to various security risks including phishing attacks, malware distribution, or compromise of user sessions. Attackers can exploit these vulnerabilities to impersonate legitimate services, steal sensitive information, or conduct further attacks against users or the organization, potentially leading to financial loss, reputational damage, or legal consequences.


The likelihood of exploitation depends on various factors including the visibility of unclaimed or misconfigured subdomains, the awareness of potential attackers, and the effectiveness of DNS monitoring and management practices. However, given the prevalence of Subdomain Takeover vulnerabilities in web applications and the potential impact on system security and user privacy, the risk associated with this vulnerability is significant if not properly mitigated.

Steps to Reproduce:

  1. Identify subdomains used by the application that are pointed to external services or resources, such as cloud hosting providers, CDNs, or third-party services.
  2. Check the status of the subdomains to determine if they are unclaimed, expired, or misconfigured.
  3. Attempt to register or point the subdomains to malicious content or services.
  4. Analyze the application's response and observe if the malicious content or services hosted on the subdomains are accessible or interact with the application.

Recommendations for Developers:

  1. Monitor Subdomains: Regularly monitor subdomains used by the application to detect unclaimed, expired, or misconfigured subdomains that may be vulnerable to takeover.
  2. Implement Proper DNS Configuration: Ensure proper DNS configuration and management practices are followed, including timely removal or redirection of unused or expired subdomains to prevent unauthorized takeover.


Addressing the Subdomain Takeover vulnerability is critical to protecting against phishing attacks, malware distribution, and compromise of user sessions. By monitoring subdomains and implementing proper DNS configuration practices, we can mitigate the risks associated with Subdomain Takeover vulnerabilities and enhance the overall security posture of our systems.