Why doesn't CMD inherit environment variables on this machine?

For whatever reason, on a specific machine my cmd process doesn't inherit its environment variables from the parent process which launched it. Instead it reverts back to the "default" environment settings, like it was launched via explorer.

A simple way to demonstrate this is to open a command-prompt and then run set Path=C:\Windows\System32\, followed by launching another cmd process from the same prompt. The variable can then be viewed by running set Path.

It should be "C:\Windows\System32" (inherited from the launching process) but on my machine it's reverted back to my environment default.

You should see something like this:

I instead get the following:

What could be causing this? It seems to break all the rules around how environment variables work and it only affects this one machine.

Solution 1:

The problem is caused by the command processor's AutoRun setting. This little "feature" of the command-line lets you configure a script to run every time a CMD process starts.

In my case, something (possibly an install of NVMW) had registered a script which assigned a completely new Path value, ignoring any existing value entirely.

Removing the HKCU\Software\Microsoft\Command Processor\Autorun value restored the command-line to its normal behaviour.