On: Can I exec a new process without an executable fil...

[userbinator]

The same thing on Windows can be done by essentially creating a process based on any file and then rewriting its contents in memory: https://stackoverflow.com/questions/305203/createprocess-fro...

As for the side-question of switching between 64 and 32 bit mode in the same process, this is classically known on Windows as "heaven's gate" and a similar technique on Linux seems possible too: https://gist.github.com/rqou/1a1834b784283add7955af430097311...

[tedunangst → userbinator]

One could also exec any available 64 bit program and then overwrite all its memory with ptrace on Linux.

[ohwutwathere → tedunangst]

Correct but in lots of scenarios (containers etc) you cannot execute ptrace() but you can execute mmap(), mprotect(), read(), write() which is all you really need. Edit: and fork().

See something I published just a month ago: https://github.com/anvilsecure/ulexecve/

[mobilio → userbinator]

Decades ago i was make similar technique but also involving CreateRemoteThread or CreateRemoteThreadEx.