Bundled PowerShell 7.6.4 (.NET 10.0.10) crashes with CET fail-fast on Windows 11 21H2 (22000.1455)

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

OpenAI.Codex_26.818.3698.0_x64

What subscription do you have?

ChatGPT Plus

What platform is your computer?

Windows 11 x64 Version: Windows 11 21H2 OS Build: 22000.1455 [Microsoft Windows NT 10.0.22000.0 True]

What issue are you seeing?

Codex App command execution fails because the bundled PowerShell runtime crashes during startup.

The failure happens before the user command is executed. For example, running git commands from Codex results in:

Fatal error.
Your Windows doesn't fully support CET.
Please install all available Windows updates.

Exit code:
-2146233082 (0x80131506)

The failing executable is the PowerShell runtime bundled by Codex:

C:\Users<user>.cache\codex-runtimes\codex-primary-runtime\dependencies\native\powershell\pwsh.exe

Directly launching this executable outside Codex reproduces the same crash:

pwsh.exe -v

The bundled runtime version is:

PowerShell: 7.6.4.500
.NET runtime: 10.0.10

System Windows PowerShell 5.1 works normally.

What steps can reproduce the bug?

Feedback ID: no-active-thread-01a0224a-db40-7d53-8343-dbd61c847315

What is the expected behavior?

Codex should execute shell commands normally.

If the bundled PowerShell runtime is incompatible with the current Windows version, Codex should either:

• detect the unsupported environment before execution;
• fall back to another supported shell (for example cmd.exe or Windows PowerShell 5.1);
• or provide a clear compatibility message instead of repeatedly retrying failed commands.

Additional information

Additional investigation:

The issue appears to be related to the bundled PowerShell/.NET runtime shipped with Codex, not the user's project commands.

Confirmed working:

• Windows PowerShell 5.1
• cmd.exe
• global npm Codex CLI 0.130.0

Confirmed failing:

• Codex bundled PowerShell 7.6.4.500

Runtime details:

Codex Desktop:
OpenAI.Codex_26.818.3698.0_x64

Bundled runtime:
codex-primary-runtime

PowerShell:
7.6.4.500

.NET:
10.0.10

Windows:
Windows 11 21H2 build 22000.1455

The issue started after a Codex update around 2026-08-14~2026-08-17. I do not have the previous runtime bundle available for comparison, so I cannot confirm the exact first bad runtime version.

1. Install Codex Desktop App.
2. Run Codex on Windows 11 21H2 (OS build 22000.1455).
3. Ask Codex to execute any shell command, for example:

git status

4. Command execution fails with CET fatal error.

The issue can also be reproduced without Codex:

1. Locate:

C:\Users<user>.cache\codex-runtimes\codex-primary-runtime\dependencies\native\powershell\pwsh.exe

2. Run:

pwsh.exe -v

3. The process immediately exits with:

Fatal error.
Your Windows doesn't fully support CET.
Please install all available Windows updates.

Exit code:
0x80131506

Start by reproducing the failure with the bundled executable at .cache/codex-runtimes/codex-primary-runtime/dependencies/native/powershell/pwsh.exe using pwsh.exe -v on Windows 11 build 22000.1455. Trace the Codex command-execution path that selects this runtime and compare its behavior with cmd.exe and Windows PowerShell 5.1. Done means commands no longer repeatedly fail, or the unsupported environment produces a clear compatibility response.