drow is a command-line utility that is used to inject code and hook the entrypoint of ELF executables (post-build). It takes unmodified ELF executables as input and exports a modified ELF contianing an embedded user-supplied payload that executes at runtime.
Drow takes the following steps to create the new patched ELF:
sh_size
and program header's p_memsz
/p_filesz
by
the size of the user-supplied payloadsh_offset
's and program headers' p_offset
's (move down sections and segments to make room
for the payload and a small "stager stub")e_shoff
, e_phoff
, etc..)e_entry
(ELF entrypoint offset) to point to the injected codeIn addition to injecting the user-supplied payload, drow injects a small code stub that is prepended to the beginning of
the payload. This stub is designed to call into the payload. If the payload is written to return to the caller, after the
payload returns the stager then tailcalls into _start
, restoring execution so the program can run as intended.
Install gcc
and scons
. Then run scons
from the root of the directory.
In addition to building drow, this project also builds a Linux x86-64 payload named rappers_delight.bin
that simply
prints to stdout
. This can be used for testing. Currently, drow only works with ELF64 files targetting x86-64.
There has been a lot of open source work done in this domain. I encourage you to also check out the following projects and associated publications: