Rack is a modular Ruby web server interface. The Rack::Sendfile middleware logs unsanitised header values from the X-Sendfile-Type header. An attacker can exploit this by injecting escape sequences (such as newline characters) into the header, resulting in log injection. This vulnerability is fixed in 2.2.12, 3.0.13, and 3.1.11.
CWE-93, CWE-117