Executive Summary
Vercel has launched network egress policies for its Sandbox product, a new security feature that allows developers to control outbound network traffic from isolated environments. Using Server Name Indication (SNI) and CIDR block filtering, developers can create "allowlists" to specify which hosts a sandbox can reach, blocking all other connections by default. This feature is aimed at developers running untrusted or AI-generated code, preventing data exfiltration and unauthorized API calls.
Key Takeaways
* Granular Egress Control: Developers can now define strict allowlists for outbound network connections from a Vercel Sandbox, with any traffic to unlisted destinations being blocked.
* Hostname-Based Filtering: The firewall primarily uses Server Name Indication (SNI) to inspect TLS handshakes, enabling precise, hostname-based rules (e.g., `*.vercel.com`) that are more effective than traditional IP-based firewalls.
* Dynamic Policy Updates: Network policies can be updated on a running sandbox without a restart. This allows for multi-stage security, such as open access for dependency installation followed by a locked-down state for code execution.
* Security for AI/Untrusted Code: The stated goal is to secure workloads that run untrusted code, particularly AI agents, by preventing compromised or "hallucinated" code from making malicious network calls.
* Availability: The network egress firewall feature is available on all Vercel plans.
Strategic Importance
This announcement strengthens Vercel's security offering for serverless environments, directly addressing enterprise concerns about running untrusted third-party or AI-generated code safely in the cloud.