GHSA-f9gf-wh3x-jx3v: Rancher meta proxy allowlist bypass leading to server-side request forgery

A security vulnerability exists in the SUSE Rancher Manager meta proxy endpoint (/meta/proxy). This endpoint is intended to forward requests only to  destinations that appear on a configured allowlist. The allowlist decision was evaluated in a  place where it could not stop a request from being forwarded, so a rejected destination was logged but the request was still handed to the proxy's transport. This affects SUSE Rancher 2.15.0 up to 2.15.3, 2.14.0 up to 2.14.7, 2.13.0 up to 2.13.11, 2.12.0 up to 2.12.15, 2.11.0 up to 2.11.19 and potentially older EOL versions.