CVE-2026-58418: Gitea: SSRF via HTTP Redirect in Repository Migration

Gitea 1.25.4 validates the initial URL provided to the repository migration endpoint (POST /api/v1/repos/migrate) and correctly blocks requests to internal addresses like 127.0.0.1 or RFC1918 ranges. However, if the initial URL points to an attacker-controlled server that responds with an HTTP 302 redirect to an internal address, Gitea follows the redirect without performing a second validation. This allows a low-privilege user to reach internal services through Gitea as a proxy.