Vercel’s sandbox design treats outbound network access as a separate security boundary from the virtual machine running an agent. Generated code can send out readable data without escaping its VM, so compute isolation alone does not contain every harmful action.
The company describes a host-side firewall that applies domain and address-range rules to connections and DNS traffic. Permissions can change while a workload runs, such as allowing package downloads during setup and removing that access before generated code executes.
For selected destinations, the host can inject credentials into requests without placing the secret inside the sandbox. Other requests can pass through a team-controlled proxy for additional checks.
Vercel says the full egress firewall is available across its Sandbox plans, including Hobby. Ordinary allowed TLS connections pass through without decryption.