Next.js: Server-Side Request Forgery in Server Actions on custom servers

## Impact When a Server Action forwards or redirects a request, an attacker can cause the server to send that outbound request to a malicious host (Server-Side Request Forgery). This requires the attacker's request to control Host-associated headers. In some configurations, it's also possible to obtain internal values that weaken middleware/proxy authorization. Applications that use Server Actions are affected when the incoming host header is not fixed to a trusted value. This typically occurs on custom servers, or on deployments not behind a proxy that pins the host. Managed hosting pins the host upstream and is not affected; `next start` and standalone output do the same from version 14.2 onward. ## Workarounds If you cannot upgrade, ensure clients do not control the host header your application receives. Pin or validate `Host` and `X-Forwarded-Host` at your edge or proxy. On version 14.2.0 and later, you can additionally set the `__NEXT_PRIVATE_ORIGIN` environment variable to your deployment's real origin: ```bash __NEXT_PRIVATE_ORIGIN=https://www.example.com node server.js

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