404 Not Found Page Detection Scanner

The 404 Not Found Page Detection scanner helps identify if servers are disclosing unnecessary information in HTTP 404 responses. It is commonly used by security professionals, bug bounty hunters, and developers to evaluate how web applications handle invalid or non-existing endpoints. Web servers and application platforms across various industries, from content management systems to custom web apps, may reveal diagnostic or structural details in 404 responses. This scanner assists in locating such disclosures. It plays a role in improving secure-by-default configurations. Detecting and managing these messages helps organizations minimize unintentional information leakage.

This detection identifies HTTP responses with a 404 Not Found status code that also contain human-readable error content like "Not Found". Such responses, especially when verbose, can reveal framework information, server technology, or routing logic. This issue usually stems from poorly configured web servers or frameworks that display default error pages. Although not critical on its own, it contributes to a broader risk of information disclosure. It may also reflect inconsistent behavior in how applications handle invalid requests. Identifying and resolving these issues can be an early step toward improving overall application security.

The scanner performs HTTP GET requests on the base URL and follows redirects up to 10 levels. It checks for a 404 status code combined with the presence of the term "Not Found" in the response body. The matching conditions ensure that the server not only reports a missing resource but also returns text content disclosing the same. This helps flag custom or default error messages being returned in production environments. Redirect handling is included to ensure accurate evaluation of landing pages or alternate paths. The scanner is designed to be lightweight and broad in scope.

If left unresolved, verbose 404 responses can reveal details about the internal structure of a web application. Attackers can use this information during reconnaissance to map out existing vs. non-existing routes. In some cases, it may hint at server-side technologies, framework errors, or deployment misconfigurations. These clues can be leveraged in further attacks, such as path guessing or technology-specific exploits. Over time, this can lead to broader risks including vulnerability discovery and exploitation. Minimizing information in error responses reduces this surface.

REFERENCES

• https://owasp.org/www-community/Improper_Error_Handling