codex/codex-rs/network-proxy/README.md

codex-network-proxy

codex-network-proxy is Codex's local network policy enforcement proxy. It runs:

• an HTTP proxy (default 127.0.0.1:3128)
• an admin HTTP API (default 127.0.0.1:8080)

It enforces an allow/deny policy and a "limited" mode intended for read-only network access.

Quickstart

1) Configure

codex-network-proxy reads from Codex's merged config.toml (via codex-core config loading).

Example config:

[network_proxy]
enabled = true
proxy_url = "http://127.0.0.1:3128"
admin_url = "http://127.0.0.1:8080"
# When `enabled` is false, the proxy no-ops and does not bind listeners.
# When true, respect HTTP(S)_PROXY/ALL_PROXY for upstream requests (HTTP(S) proxies only),
# including CONNECT tunnels in full mode.
allow_upstream_proxy = false
# By default, non-loopback binds are clamped to loopback for safety.
# If you want to expose these listeners beyond localhost, you must opt in explicitly.
dangerously_allow_non_loopback_proxy = false
dangerously_allow_non_loopback_admin = false
mode = "limited" # or "full"

[network_proxy.policy]
# Hosts must match the allowlist (unless denied).
# If `allowed_domains` is empty, the proxy blocks requests until an allowlist is configured.
allowed_domains = ["*.openai.com"]
denied_domains = ["evil.example"]

# If false, local/private networking is rejected. Explicit allowlisting of local IP literals
# (or `localhost`) is required to permit them.
# Hostnames that resolve to local/private IPs are still blocked even if allowlisted.
allow_local_binding = false

# macOS-only: allows proxying to a unix socket when request includes `x-unix-socket: /path`.
allow_unix_sockets = ["/tmp/example.sock"]

2) Run the proxy

cargo run -p codex-network-proxy --

3) Point a client at it

For HTTP(S) traffic:

export HTTP_PROXY="http://127.0.0.1:3128"
export HTTPS_PROXY="http://127.0.0.1:3128"

4) Understand blocks / debugging

When a request is blocked, the proxy responds with 403 and includes:

• x-proxy-error: one of:
  • blocked-by-allowlist
  • blocked-by-denylist
  • blocked-by-method-policy
  • blocked-by-policy

In "limited" mode, only GET, HEAD, and OPTIONS are allowed for plain HTTP. HTTPS CONNECT remains a transparent tunnel, so limited-mode method enforcement does not apply to HTTPS.

Library API

codex-network-proxy can be embedded as a library with a thin API:

use codex_network_proxy::{NetworkProxy, NetworkDecision, NetworkPolicyRequest};

let proxy = NetworkProxy::builder()
    .http_addr("127.0.0.1:8080".parse()?)
    .admin_addr("127.0.0.1:9000".parse()?)
    .policy_decider(|request: NetworkPolicyRequest| async move {
        // Example: auto-allow when exec policy already approved a command prefix.
        if let Some(command) = request.command.as_deref() {
            if command.starts_with("curl ") {
                return NetworkDecision::Allow;
            }
        }
        NetworkDecision::Deny {
            reason: "policy_denied".to_string(),
        }
    })
    .build()
    .await?;

let handle = proxy.run().await?;
handle.shutdown().await?;

When unix socket proxying is enabled, HTTP/admin bind overrides are still clamped to loopback to avoid turning the proxy into a remote bridge to local daemons.

Policy hook (exec-policy mapping)

The proxy exposes a policy hook (NetworkPolicyDecider) that can override allowlist-only blocks. It receives command and exec_policy_hint fields when supplied by the embedding app. This lets core map exec approvals to network access, e.g. if a user already approved curl * for a session, the decider can auto-allow network requests originating from that command.

Important: Explicit deny rules still win. The decider only gets a chance to override not_allowed (allowlist misses), not denied or not_allowed_local.

Admin API

The admin API is a small HTTP server intended for debugging and runtime adjustments.

Endpoints:

curl -sS http://127.0.0.1:8080/health
curl -sS http://127.0.0.1:8080/config
curl -sS http://127.0.0.1:8080/patterns
curl -sS http://127.0.0.1:8080/blocked

# Switch modes without restarting:
curl -sS -X POST http://127.0.0.1:8080/mode -d '{"mode":"full"}'

# Force a config reload:
curl -sS -X POST http://127.0.0.1:8080/reload

Platform notes

• Unix socket proxying via the x-unix-socket header is macOS-only; other platforms will reject unix socket requests.
• HTTPS tunneling uses BoringSSL via Rama's rama-tls-boring; building the proxy requires a native toolchain and CMake on macOS/Linux/Windows.

Security notes (important)

This section documents the protections implemented by codex-network-proxy, and the boundaries of what it can reasonably guarantee.

• Allowlist-first policy: if allowed_domains is empty, requests are blocked until an allowlist is configured.

• Deny wins: entries in denied_domains always override the allowlist.

• Local/private network protection: when allow_local_binding = false, the proxy blocks loopback and common private/link-local ranges. Explicit allowlisting of local IP literals (or localhost) is required to permit them; hostnames that resolve to local/private IPs are still blocked even if allowlisted (best-effort DNS lookup).

• Limited mode enforcement:

  • only GET, HEAD, and OPTIONS are allowed
  • HTTPS CONNECT remains a tunnel; limited-mode method enforcement does not apply to HTTPS

• Listener safety defaults:

  • the admin API is unauthenticated; non-loopback binds are clamped unless explicitly enabled via dangerously_allow_non_loopback_admin

• the HTTP proxy listener similarly clamps non-loopback binds unless explicitly enabled via dangerously_allow_non_loopback_proxy

• when unix socket proxying is enabled, both listeners are forced to loopback to avoid turning the proxy into a remote bridge into local daemons.

• enabled is enforced at runtime; when false the proxy no-ops and does not bind listeners. Limitations:

• DNS rebinding is hard to fully prevent without pinning the resolved IP(s) all the way down to the transport layer. If your threat model includes hostile DNS, enforce network egress at a lower layer too (e.g., firewall / VPC / corporate proxy policies).