Nezha Dashboard OAuth2 Host Header Injection Vulnerability

Nezha 2.2.3 contains a Host header injection regression in the OAuth2 redirect endpoint.

When the optional dashboard_host setting is empty, /api/v1/oauth2/{provider} (cmd/dashboard/controller/oauth2.go) reflects the attacker-supplied HTTP Host header into the redirect_uri sent to the identity provider instead of falling back to the configured install_host.

• An attacker can induce a victim to begin OAuth2 login with a forged Host header, causing an attacker-controlled callback URL to be used as the redirect_uri.
• If the OAuth2 provider accepts it, the victim's authorization code is delivered to the attacker origin, allowing the attacker to complete the OAuth2 login/binding flow and take over the account.
• This regresses the fix for GHSA-9rc6-8cjv-rcvx and is configuration-dependent (dashboard_host empty).
• At the time of the advisory no patched version was available.