A configuration flaw in the official Docker images allows an unauthenticated remote attacker to impersonate any user, including administrators, by spoofing the `X-WEBAUTH-USER` header. This occurs because the `app.ini` template hard-codes the `REVERSE PROXY TRUSTED PROXIES` variable to a wildcard (`*`), causing the application to trust identity headers from any source IP address instead of only trusted loopback addresses. This issue is exploitable when reverse-proxy authentication is enabled. It is estimated that approximately 22,900 unique Gitea hosts are accessible from the internet, with 83% potentially affected. Real-world reconnaissance and exploitation attempts were detected within 13 days of public disclosure. The flaw allows access to repositories, CI/CD secrets, SSH keys, and administrative functions via the web interface, although the token-based API endpoints (e.g., `/api/v1/...`) are not affected.