Input Validation / Arbitrary HTTP Host header accepted

Web and API


When a web application is accessible using arbitrary HTTP Host headers, it can be vulnerable to a security issue known as Host Header Injection. This vulnerability occurs when an attacker can manipulate the Host header in an HTTP request to trick the server into processing the request as if it were intended for a different domain.


This can lead to various security risks, including:

  • Cache Poisoning: The attacker may attempt to poison caching mechanisms by sending malicious requests with different Host headers, leading to the caching of sensitive information for the wrong domain.
  • Session Fixation: The attacker might try to fixate user sessions by sending requests with a manipulated Host header, potentially forcing the application to associate the session with a different domain.
  • Password Reset Attacks: Some applications use the Host header to determine the context of a password reset request. An attacker could exploit this to reset passwords for accounts on a different domain.
  • Security Token Bypass: If the web application relies on security tokens or authentication mechanisms based on the Host header, an attacker may be able to bypass these by manipulating the header.
  • Clickjacking: The attacker could use Host header manipulation to execute clickjacking attacks, tricking users into interacting with elements they believe belong to a different domain.


To mitigate these risks, consider implementing the following measures:

  • Validate and Sanitize Input_: Always validate and sanitize input, including the Host header. Ensure that the Host header is valid and expected for each request.
  • Use Canonical Hostnames: Configure your web server to recognize and respond only to a specific set of canonical hostnames. Reject requests with unrecognized or unexpected Host headers.
  • HTTP Strict Transport Security (HSTS): Implement HSTS to ensure that browsers always connect to your site over HTTPS. This helps prevent Man-in-the-Middle attacks and ensures secure communication.
    Use SameSite Cookies: Set the SameSite attribute on cookies to restrict them from being sent in cross-site requests. This helps mitigate the risk of session fixation attacks.
  • Security Headers: Utilize security headers, such as Content Security Policy (CSP), to mitigate the risk of clickjacking and other client-side attacks.
  • Monitoring and Logging: Implement robust monitoring and logging to detect and respond to suspicious activity related to Host Header Injection.

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