If you've fallen victim to phishing you're hosed anyway as a malicious process can read and write to the address space of another process, see /proc/$pid/mem, WriteProcessMemory(), etc.
There's a spread of things that can happen in phishing; I would expect that it's a lot harder to get a user to run an actual executable outright than to open a "data" file that makes a trusted application become malicious.
In order to read or write /proc/pid/mem your process needs to be allowed to ptrace() the target process. You can’t do that for arbitrary processes. Similar story for WriteProcessMemory().
Above your security context, no, but you can definitely WriteProcessMemory any other process that is in your same security context or lower (something similar holds for ptrace, although remember that SUID/SGID binaries are running not at a same security context)
