Runtimes

Vercel Sandbox provides a secure, isolated environment for running your code. This page details the legacy runtime environments, available packages, and system configuration. New sandboxes default to Vercel Managed Images instead of runtimes.

The legacy runtimes include node26, node24, node22, and python3.13 images. In all of these images:

• User code is executed as the vercel-sandbox user.
• The default working directory is /vercel/sandbox.
• sudo access is available.

node24 is the default runtime if the runtime property is not specified on version 2 of the Sandbox SDK. Starting with version 3, sandboxes that specify neither runtime nor image use the vercel/sandbox/universal:latest managed image instead.

The base system for legacy runtimes is Amazon Linux 2023 with the following additional packages:

• bind-utils
• bzip2
• findutils
• git
• gzip
• iputils
• libicu
• libjpeg
• libpng
• ncurses-libs
• openssl
• openssl-libs
• procps
• tar
• unzip
• which
• whois
• zstd

In legacy runtimes, you can install additional packages using dnf. Managed images use their own package managers instead, such as apt-get on the Ubuntu-based images. See How to install system packages in Vercel Sandbox for examples.

You can find the list of available packages on the Amazon Linux documentation.

Vercel Sandbox mounts a unique, per-sandbox certificate authority (CA) certificate for the sandbox proxy in these locations:

• /etc/pki/ca-trust/source/anchors/vercel-proxy-ca.pem
• /usr/local/share/ca-certificates/vercel-proxy-ca.pem

Vercel Sandbox adds the proxy CA certificate to the system trust bundle automatically. Applications that use the system trust store do not need extra configuration.

The following environment variables are also set so common tools and runtimes use the system CA bundle at /etc/ssl/certs/ca-certificates.crt:

AWS_CA_BUNDLE=/etc/ssl/certs/ca-certificates.crt
CARGO_HTTP_CAINFO=/etc/ssl/certs/ca-certificates.crt
CURL_CA_BUNDLE=/etc/ssl/certs/ca-certificates.crt
GIT_SSL_CAINFO=/etc/ssl/certs/ca-certificates.crt
GRPC_DEFAULT_SSL_ROOTS_FILE_PATH=/etc/ssl/certs/ca-certificates.crt
NODE_EXTRA_CA_CERTS=/etc/ssl/certs/ca-certificates.crt
NODE_USE_SYSTEM_CA=1
NPM_CONFIG_CAFILE=/etc/ssl/certs/ca-certificates.crt
PIP_CERT=/etc/ssl/certs/ca-certificates.crt
REQUESTS_CA_BUNDLE=/etc/ssl/certs/ca-certificates.crt
SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt

If your application does not use the system trust store and these environment variables, configure it to trust one of the mounted vercel-proxy-ca.pem files. This is required for HTTPS traffic that the sandbox firewall terminates for transformation rules.

Containers do not inherit the proxy CA. The proxy CA certificate and the CA environment variables are installed on the sandbox host. A container that you run inside the sandbox has its own isolated filesystem and trust store, so it does not inherit either of them. Without the certificate, HTTPS requests from inside the container fail TLS verification when the sandbox firewall terminates them for transformation rules.

To make a container trust the proxy, mount the certificate into the container and add it to the container's own trust store. For example, with Docker:

# Mount the host certificate into the container and trust it at build or run time.
docker run --rm \
  -v /etc/pki/ca-trust/source/anchors/vercel-proxy-ca.pem:/usr/local/share/ca-certificates/vercel-proxy-ca.crt:ro \
  my-image \
  sh -c "update-ca-certificates && my-command"

The exact path and command depend on the container's base image. Place the certificate where that image's trust store expects it, then run the image's trust-update command (for example, update-ca-certificates on Debian or Ubuntu, or update-ca-trust on Amazon Linux, Fedora, or RHEL). For applications that read a CA bundle from an environment variable instead of the system trust store, set the relevant variable (such as NODE_EXTRA_CA_CERTS) to the mounted certificate path inside the container.

The sandbox sudo configuration is designed to be straightforward:

• HOME is set to /root. Commands executed with sudo will source root's configuration files (e.g. .gitconfig, .bashrc, etc).
• PATH is left unchanged. Local or project-specific binaries will still be available when running with elevated privileges.
• The executed command inherits all other environment variables that were set.

Each sandbox runs in its own Firecracker microVM with a dedicated kernel, so you can run processes that require system-level privileges without affecting other sandboxes or the host. These workloads run with sudo and are isolated to your sandbox by the microVM boundary.

Supported workloads include:

• Container runtimes: Run Docker and other container engines inside the sandbox to build images or run containerized workloads.
• VPN clients: Connect to a VPN provider to reach private networks during a session.
• FUSE filesystems: Mount Filesystem in Userspace (FUSE) drivers to attach object storage, network filesystems, or other custom mounts.

These processes require elevated privileges, so run them with sudo. For example, to run a command with elevated privileges through the CLI:

sandbox exec --sudo <name> -- <command>

Outbound network access from these workloads still follows the sandbox firewall network policy. Restrict reachable destinations with a network policy when you run untrusted code.

If you run containers inside the sandbox, the proxy CA certificate is not available inside the container by default. Install it in the container's trust store so HTTPS traffic that the firewall terminates passes TLS verification. See Proxy CA certificates.