The vulnerability in MIYAGAWA's Starman (versions before 0.4018) arises from incorrect handling of HTTP headers when both Content-Length and Transfer-Encoding: chunked are present. Starman incorrectly gives precedence to Content-Length, violating RFC 7230 section 3.3.3, which mandates that Transfer-Encoding must take precedence. This inconsistency enables HTTP Request Smuggling attacks, where an attacker can send specially crafted requests that are interpreted differently by front-end proxies and backend servers, potentially allowing request splitting or bypassing security controls.

An attacker could exploit this vulnerability to smuggle malicious HTTP requests through a front-end reverse proxy, potentially leading to unauthorized request execution or bypassing security mechanisms. However, there are no known exploits in the wild at this time, and the exact impact depends on the deployment environment and proxy configurations.

No official patch or remediation guidance is currently available for this vulnerability. Users should monitor the vendor's advisories for updates. In the meantime, consider deploying additional proxy-level protections or disabling support for conflicting headers if possible. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance.