ewe Web Server CRLF Injection Vulnerability in HTTP Response Headers

A vulnerability exists in the ewe web server, specifically in versions prior to 3.0.6. The issue arises in the encode_headers function, which improperly handles response header keys and values by directly inserting them into raw HTTP bytes without validating or removing carriage return and line feed (CRLF) sequences. This flaw allows for HTTP response splitting, cache poisoning, and potentially cross-site scripting, especially when user-controlled data is included in response headers, such as Location redirect headers. While ewe does validate CRLF in incoming request headers, it lacks similar protection for outgoing response headers, leaving a critical gap that can be exploited.

Impact

Exploitation of this vulnerability leads to HTTP response splitting, where an attacker can inject additional headers or content into the response. This can cause cache poisoning, where cached content is manipulated, and potentially allow cross-site scripting attacks, where malicious scripts are injected and executed in the context of the user's browser.

Reproduction

To reproduce this vulnerability, send a request to an ewe server with a crafted 'next' query parameter that includes a CRLF sequence. The server will respond with a 'Location' header that reflects the injected URL, along with an additional header (e.g., 'X-Injected') that demonstrates the successful exploitation of the CRLF injection.

Remediation

Users can update to ewe version 3.0.6 or later, where this vulnerability has been patched. The update process involves downloading the latest version from the ewe GitHub repository.