Bundled `codex` binary unreadable (EPERM) from official DMG — install impossible on macOS 27.0

What version of the Codex App are you using (From “About Codex” dialog)?

Unable to install — DMG build dated 2026-09-18 (ChatGPT.dmg, 645,200,049 bytes)

What subscription do you have?

ChatGPT Plus

What platform is your computer?

Darwin 27.0.0 arm64 arm

What issue are you seeing?

Summary

On a clean macOS 27.0 machine, the unified ChatGPT desktop app cannot be installed. Every attempt to open ChatGPT.app/Contents/Resources/codex inside the mounted DMG returns Operation not permitted, including as root. All other files in the same directory copy normally. This has persisted for roughly six weeks across multiple app versions and one macOS update.

Environment

• Mac mini (2023), Apple Silicon
• macOS 27.0, build 26A428
• Admin account, no MDM (profiles status: not enrolled)
• No system extensions (systemextensionsctl list: 0 extensions)
• No third-party kexts (kextstat: none)
• XProtect 5360, payloads 163, XProtect.yara dated 2026-09-11
• DMG: ChatGPT.dmg, 645,200,049 bytes, downloaded via Safari from persistent.oaistatic.com/codex-app-prod/ChatGPT.dmg

What fails

The bundled installer (ChatGPTInstaller.dmg, 848,907 bytes) ends with:

The app's OpenAI signature could not be verified. No existing app will be replaced.

Manual installation fails on one specific file. cp, ditto, dd and xattr all return Operation not permitted on Contents/Resources/codex, including under sudo. The file itself looks normal:
-rwxr-xr-x 1 user staff - 234063312 Sep 18 06:05 codex
No BSD flags, standard permissions, read-only DMG.

What succeeds

Other files in the identical directory copy without error: codex-code-mode-host (62 MB) and app.asar (358 MB) both copy fine.

The bundle itself validates:
spctl -a -vvv returns accepted, source=Notarized Developer ID, origin=Developer ID Application: OpenAI OpCo, LLC (2DC432GLL2), Identifier=com.openai.codex.

Relevant log output

From the bundled installer:
ChatGPTInstaller: (Security) SecKeyVerifySignature repeated ~30x, then
ChatGPTInstaller: (Security) [com.apple.securityd:security_exception] UNIX error exception: 1

When launching a manually placed partial copy:
syspolicyd: [com.apple.syspolicy.exec:default] Terminating process due to Gatekeeper rejection

Ruled out

• Quarantine: com.apple.quarantine removed from the DMG before mounting, no change
• Permissions: file is -rwxr-xr-x, no flags, refused even to root
• Third-party security software: Malwarebytes fully uninstalled, machine rebooted, no change
• Safe Mode: same failure
• Network interference: no proxy configured, download completes (HTTP 202)
• Stale XProtect data: up to date, no pending config-data updates
• Disk space: not a factor

Impact

Paying subscriber unable to install the desktop app on this machine for approximately six weeks. ChatGPT Classic installs and runs normally, which suggests the block is specific to this binary.

What steps can reproduce the bug?

1. Download ChatGPT.dmg (645,200,049 bytes) from persistent.oaistatic.com/codex-app-prod/ChatGPT.dmg via Safari.
2. Mount it: hdiutil attach ~/Downloads/ChatGPT.dmg
3. Try to read the bundled binary — cp, sudo dd and xattr all return Operation not permitted on /Volumes/ChatGPT Installer/ChatGPT.app/Contents/Resources/codex.
4. Confirm other files in the same directory copy fine: codex-code-mode-host (62 MB) and app.asar (358 MB).

The bundled installer fails at the same point with "The app's OpenAI signature could not be verified."

Reproducible on every attempt over six weeks, across multiple app versions and one macOS update, including in Safe Mode.

What is the expected behavior?

The bundled codex binary should be readable so that ditto, cp -R, the Finder, or the official installer can place the app in /Applications and it can launch.

Additional information

I have contacted OpenAI support several times over the past six weeks, including with screen recordings, without resolution. ChatGPT Classic (bundle ID com.openai.chat) installs and launches normally on the same machine, so this is not a general Gatekeeper problem on this system. Happy to run any additional diagnostic commands on request.

Start by reproducing the failure with ChatGPT.dmg and the bundled Contents/Resources/codex binary, comparing it with codex-code-mode-host and app.asar. Inspect the packaging and signing inputs for the DMG and ChatGPTInstaller.dmg. Done means the codex binary can be copied from the official DMG and the installer verifies and launches the app on macOS.