Description
When handling ambiguous URLs, web servers may inadvertently serve responses that can be misinterpreted by clients, leading to potential confusion about the correct relative path. This vulnerability can also affect resources such as CSS and images, which are specified using relative URLs. By exploiting this issue, an attacker may be able to trick a client into interpreting HTML as CSS or other content types, resulting in a cross-site scripting (XSS) vulnerability.
Recommendation
To mitigate this vulnerability, web servers and frameworks should be updated to handle ambiguous URLs more securely. Within the application, ensure that the correct ‘’ HTML tag is used in the HTTP response to unambiguously specify the base URL for all relative URLs. Additionally, set the ‘Content-Type’ HTTP response header to make it harder for attackers to force clients to misinterpret the content type of the response. Use the ‘X-Content-Type-Options: nosniff’ HTTP response header to prevent clients from sniffing the content type of the response. Finally, specify a modern DOCTYPE such as ‘!doctype html’ and set the ‘X-Frame-Options’ HTTP response header to prevent Quirks Mode from being enabled in clients using framing attacks.
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