Codex in-app Browser blocks http://127.0.0.1:3000 despite local server reachable
What version of the Codex App are you using (From “About Codex” dialog)?
26.519.3891.0
What subscription do you have?
ChatGPT Plus
What platform is your computer?
Windows 11 Pro, x64, build 26200
What issue are you seeing?
Feedback ID:
019e4fa5-c24d-7c43-ae5b-e6f9bf1aec88
Problem:
Codex in-app Browser / @Browser rejects http://127.0.0.1:3000 with:
"Browser Use cannot access http://127.0.0.1:3000 because enterprise network policy blocks it."
Local diagnostics:
- PowerShell can reach http://127.0.0.1:3000/
- HTTP returns 200
- Test-NetConnection to 127.0.0.1:3000 succeeds
- The local server is running correctly
Affected machine:
- Windows 11 Pro x64, build 26200
- Codex package: OpenAI.Codex_26.519.3891.0_x64__2p2nqsd0c76g0
- Edge WebView2 runtime detected
Firewall / sandbox findings:
Initially these Windows Firewall rules were present and enabled:
- codex_sandbox_offline_block_loopback_tcp
- codex_sandbox_offline_block_loopback_udp
- codex_sandbox_offline_block_outbound
I disabled:
- codex_sandbox_offline_block_loopback_tcp
- codex_sandbox_offline_block_loopback_udp
After a full Codex restart, both remain Enabled: False, but @Browser still rejects http://127.0.0.1:3000 with the same enterprise network policy block.
Comparison machine:
- Same local test URL http://127.0.0.1:3000 returns HTTP 200
- codex_sandbox_offline_block_loopback_* rules are not present
Expected:
@Browser should be able to open local development URLs like http://127.0.0.1:3000, or Codex should provide a setting/allowlist to permit localhost access.
Actual:
@Browser rejects the URL before navigation due to enterprise/network policy.
What steps can reproduce the bug?
Feedback ID:
019e4fa5-c24d-7c43-ae5b-e6f9bf1aec88
Problem:
Codex in-app Browser / @Browser rejects http://127.0.0.1:3000 with:
"Browser Use cannot access http://127.0.0.1:3000 because enterprise network policy blocks it."
Local diagnostics:
- PowerShell can reach http://127.0.0.1:3000/
- HTTP returns 200
- Test-NetConnection to 127.0.0.1:3000 succeeds
- The local server is running correctly
Affected machine:
- Windows 11 Pro x64, build 26200
- Codex package: OpenAI.Codex_26.519.3891.0_x64__2p2nqsd0c76g0
- Edge WebView2 runtime detected
Firewall / sandbox findings:
Initially these Windows Firewall rules were present and enabled:
- codex_sandbox_offline_block_loopback_tcp
- codex_sandbox_offline_block_loopback_udp
- codex_sandbox_offline_block_outbound
I disabled:
- codex_sandbox_offline_block_loopback_tcp
- codex_sandbox_offline_block_loopback_udp
After a full Codex restart, both remain Enabled: False, but @Browser still rejects http://127.0.0.1:3000 with the same enterprise network policy block.
Comparison machine:
- Same local test URL http://127.0.0.1:3000 returns HTTP 200
- codex_sandbox_offline_block_loopback_* rules are not present
Expected:
@Browser should be able to open local development URLs like http://127.0.0.1:3000, or Codex should provide a setting/allowlist to permit localhost access.
Actual:
@Browser rejects the URL before navigation due to enterprise/network policy.
What is the expected behavior?
_No response_
Additional information
_No response_
2 Comments
Potential duplicates detected. Please review them and close your issue if it is a duplicate.
Powered by Codex Action
Additional update after further diagnostics:
This appears related to:
My case is not limited to the Chrome plugin. It happens with the Codex in-app Browser / @Browser flow.
The important part is that this is not a normal network failure:
Things already tried on the affected machine:
Observed behavior:
Manual in-app browser navigation can work, but Browser Use automation cannot access the page. Browser Use rejects before navigation/inspection with:
"Browser Use cannot access http://127.0.0.1:3000 because enterprise network policy blocks it."
It also blocks automation/content inspection for public sites such as google.pl / onet.pl. In the onet.pl case, I can manually open the page, but Browser Use cannot inspect DOM/headers/content.
This makes it look like a Browser Use approval / preflight / persisted thread-permission state issue, not a Windows networking issue.
Possible relation to #21955 / #22019:
Those issues mention persisted thread state such as sandboxPolicy.networkAccess: false or origins being incorrectly persisted as denied. My symptoms look similar: the browser/runtime connects, but Browser Use rejects the origin before load even though the local server is reachable and no relevant Edge/Chrome LocalNetwork block policy is present.
Could the in-app Browser / @Browser path be reading stale per-thread Browser Use approval state, networkAccess state, or origin denial state from somewhere other than the normal ~/.codex / C:\codex_data cache?
If there is a specific local state file or database that stores Browser Use origin decisions / networkAccess for the in-app browser, please point me to it so I can verify whether http://127.0.0.1:3000 or localhost is persisted as denied or networkAccess=false.