Advanced egress firewall filtering for Vercel Sandbox
Vercel just shipped SNI-based egress filtering for sandboxes. Now you can lock down AI-generated code before it runs—no more hallucinated API calls or data exfiltration.
Why it matters
As AI code generation becomes standard (GitHub Copilot, Claude Code, etc.), runtime security for untrusted or LLM-generated code is becoming table stakes. Vercel's SNI firewall lets teams execute AI-generated snippets safely by restricting outbound access to whitelisted domains, catching both compromised and hallucinated code before data leaves the sandbox.
The key facts
11 to knowFeature: SNI-based egress filtering for Vercel Sandbox (host-based, not IP-based)
Use case: Restricting untrusted and AI-generated code execution
Technical approach: TLS handshake inspection to extract target hostname; CIDR fallback for non-TLS
Policy flexibility: Dynamic updates without process restart; deny-all default mode
Availability: All Vercel plans
Publication date: Feb 11, 2026
Feature: Advanced egress firewall filtering via SNI (Server Name Indication) inspection and CIDR blocks
Use case: Running untrusted or AI-generated code safely by restricting outbound network access
Technical approach: TLS handshake inspection to extract target hostname, avoiding HTTP proxy limitations
Capability: Dynamic policy updates without sandbox restart
Security model: Deny-by-default with allowlist approach
Go to the source
Vercel Blogvercel.com
Publisher excerpt: can now enforce egress network policies through Server Name Indication (SNI) filtering and CIDR blocks, giving you control over which hosts a sandbox can reach. Outbound TLS connections are matched against your policy at the handshake, unauthorized destinations are rejected before any data is…