codex - 💡(How to fix) Fix Windows Codex app: npm/network DNS fails in sandbox despite network enabled; cannot reach local proxy

Summary

On Windows, commands run from the Codex app cannot resolve DNS or install npm packages, even though the host PowerShell can run npm normally. The failure persists across workspace-write with sandbox_workspace_write.network_access = true and Full Access / danger-full-access mode.

The current evidence suggests a Codex Windows sandbox/network isolation issue rather than an npm registry, TLS, or package install-script problem.

Environment

• OS: Windows 10.0.26200
• Codex app package observed in PATH: OpenAI.Codex_26.415.4716.0_x64__2p2nqsd0c76g0
• Shell: PowerShell
• Node: v22.19.0
• npm: 10.9.3
• npm registry: https://registry.npmmirror.com
• npm proxy: null
• npm https-proxy: null
• Project trusted in config
• Tested sandbox modes:
  • workspace-write with [sandbox_workspace_write] network_access = true
  • Full access / danger-full-access
• Approval policy: never

Redacted config shape

model = "gpt-5.4"
model_reasoning_effort = "high"
sandbox_mode = "workspace-write" # also tested full access / danger-full-access
approval_policy = "never"

[shell_environment_policy]
inherit = "core"

[sandbox_workspace_write]
network_access = true

[shell_environment_policy.set]
APPDATA = "C:\\Users\\user\\AppData\\Roaming"
LOCALAPPDATA = "C:\\Users\\user\\AppData\\Local"
USERPROFILE = "C:\\Users\\user"
HOME = "C:\\Users\\user"
TEMP = "C:\\Users\\user\\AppData\\Local\\Temp"
TMP = "C:\\Users\\user\\AppData\\Local\\Temp"
NPM_CONFIG_CACHE = "D:\\a311\\系统赛\\2026系统赛\\信安\\.npm-cache"
# Anthropic/OpenAI-compatible API credentials omitted/redacted

[windows]
sandbox = "elevated"

Expected behavior

From a Codex shell with network access enabled, npm should be able to resolve the configured registry and install a simple package such as lodash, or at least connect to the host's configured local proxy when explicitly configured.

Actual behavior

Host PowerShell works

The user's normal PowerShell reports:

npm config get registry  # https://registry.npmmirror.com
npm config get proxy     # null
npm config get https-proxy # null
npm ping                 # succeeds, PONG around 176ms
node -v                  # v22.19.0
npm -v                   # 10.9.3

The host also has a local proxy listening on port 7897:

TCP    0.0.0.0:7897    0.0.0.0:0    LISTENING    <pid>
TCP    [::]:7897       [::]:0       LISTENING    <pid>

Codex shell fails DNS resolution

In the Codex shell:

const dns = require('node:dns');
console.log('servers', dns.getServers());
for (const host of ['registry.npmmirror.com','registry.npmjs.org','github.com']) {
  dns.lookup(host, (err, address, family) => {
    console.log(host, err ? ('ERR ' + err.code + ' ' + err.message) : ('OK ' + address + ' IPv' + family));
  });
}
setTimeout(() => {}, 1000);

Output:

servers [ '223.5.5.5', '223.6.6.6', '198.18.0.2' ]
registry.npmmirror.com ERR EAI_FAIL getaddrinfo EAI_FAIL registry.npmmirror.com
registry.npmjs.org ERR EAI_FAIL getaddrinfo EAI_FAIL registry.npmjs.org
github.com ERR EAI_FAIL getaddrinfo EAI_FAIL github.com

npm ping --verbose fails with:

npm notice PING https://registry.npmmirror.com/
npm http fetch GET https://registry.npmmirror.com/-/ping attempt 1 failed with EAI_FAIL
npm http fetch GET https://registry.npmmirror.com/-/ping attempt 2 failed with EAI_FAIL
npm http fetch GET https://registry.npmmirror.com/-/ping attempt 3 failed with EAI_FAIL
npm error code EAI_FAIL
npm error syscall getaddrinfo
npm error network request to https://registry.npmmirror.com/-/ping failed, reason: getaddrinfo EAI_FAIL registry.npmmirror.com

npm install lodash --verbose --no-audit --no-fund fails before package metadata is fetched:

npm http fetch GET https://registry.npmmirror.com/npm attempt 1 failed with EAI_FAIL
npm http fetch GET https://registry.npmmirror.com/lodash attempt 1 failed with EAI_FAIL
...
npm error network request to https://registry.npmmirror.com/lodash failed, reason: getaddrinfo EAI_FAIL registry.npmmirror.com

npm install esbuild --verbose --no-audit --no-fund fails the same way, before any secondary binary download is reached.

Local proxy is not reachable from Codex shell

The host proxy is listening on 7897, but the Codex shell cannot connect to it:

127.0.0.1 ERROR UNKNOWN connect UNKNOWN 127.0.0.1:7897 - Local (undefined:undefined)
172.17.132.84 ERROR UNKNOWN connect UNKNOWN 172.17.132.84:7897 - Local (undefined:undefined)

When HTTP_PROXY and HTTPS_PROXY are set manually inside the Codex shell:

$env:HTTP_PROXY='http://127.0.0.1:7897'
$env:HTTPS_PROXY='http://127.0.0.1:7897'
npm ping --verbose

The failure changes from DNS EAI_FAIL to proxy connection failure:

reason: connect UNKNOWN 127.0.0.1:7897 - Local (undefined:undefined)

This suggests npm obeys the explicit proxy env vars, but Codex cannot reach the host-local proxy endpoint.

Additional observations

• In workspace-write, the shell cwd appears under C:\Users\CodexSandboxOnline\.codex\.sandbox\cwd\....
• In Full Access / danger-full-access, the environment variables from shell_environment_policy.set are correctly injected:
  • APPDATA=C:\Users\user\AppData\Roaming
  • LOCALAPPDATA=C:\Users\user\AppData\Local
  • NPM_CONFIG_CACHE=...\.npm-cache
• Full Access fixes npm cache/log path issues, but DNS still fails with EAI_FAIL.
• With Clash TUN enabled, route/DNS state changes are visible in Codex (198.18.0.2 appears), but DNS resolution still fails.
• Toggling TUN on/off, enabling global proxy mode, changing TUN MTU to 1500, switching between workspace-write and Full Access, and setting network_access = true did not restore npm networking.

Why this looks like a Codex Windows networking issue

The same Node/npm versions and npm registry settings work in the user's normal PowerShell. In the Codex shell, DNS fails for multiple unrelated domains and direct connections to the host's local proxy also fail. The failure happens before npm can reach package metadata or any install-script secondary download.

Request

Please investigate Codex app on Windows sandbox networking / DNS / host-local proxy access. Specifically:

1. Why does DNS resolution return EAI_FAIL in Codex shells when the host PowerShell can resolve and npm ping succeeds?
2. Why can the host connect to 127.0.0.1:7897, while the Codex shell cannot connect to 127.0.0.1:7897 or the host LAN IP 172.17.132.84:7897?
3. Is there a supported config option to allow Codex Windows sandbox sessions to use host system proxy / local loopback proxy?
4. Is [sandbox_workspace_write] network_access = true expected to work in the Windows app, and does it cover DNS plus host-local proxy access?

Sensitive tokens and API credentials have been omitted from this report.