ShellNoob

Writing shellcodes has always been super fun, but some parts are extremely boring and error prone. Focus only on the fun part, and use ShellNoob!

For a quick overview, check the slides for the Black Hat Arsenal talk: link

Want to contribute? Feature request? Bug report? Swears? All feedback is welcome!! (But some kind of feedback is more welcome than others :-)).

Feel free to ping me on twitter @reyammer or to email me at yanick[AT]cs.ucsb.edu any questions!

Contributors & Acknowledgments

• Levente Polyak (@anthraxx42)
  • added Python 3 support
  • bug fixes
• @ToolsWatch & Black Hat crews
  • They gave me a chance to show off my tool :D

News

• 01/21/2014 - ShellNoob 2.1 is out! It comes with full support for Python 3 and tons of bug fixes. Full credits go to Levente Polyak!

• 07/29/2013 - ShellNoob 2.0 is out!

• 06/08/2013 - ShellNoob got accepted at Black Hat Arsenal! See announcement here: link.

Features

• convert shellcode between different formats and sources. Formats currently supported: asm, bin, hex, obj, exe, C, python, ruby, pretty, safeasm, completec, shellstorm. (All details in the "Formats description" section.)
• interactive asm-to-opcode conversion (and viceversa) mode. This is useful when you cannot use specific bytes in the shellcode and you want to figure out if a specific assembly instruction will cause problems.
• support for both ATT & Intel syntax. Check the --intel switch.
• support for 32 and 64 bits (when playing on x86_64 machine). Check the --64 switch.
• resolve syscall numbers, constants, and error numbers (now implemented for real! :-)).
• portable and easily deployable (it only relies on gcc/as/objdump and python). It is just one self-contained python script, and it supports both Python2.7+ and Python3+.
• in-place development: you run ShellNoob directly on the target architecture!
• built-in support for Linux/x86, Linux/x86_64, Linux/ARM, FreeBSD/x86, FreeBSD/x86_64.
• "prepend breakpoint" option. Check the -c switch.
• read from stdin / write to stdout support (use "-" as filename)
• uber cheap debugging: check the --to-strace and --to-gdb option!
• Use ShellNoob as a Python module in your scripts! Check the "ShellNoob as a library" section.
• Verbose mode shows the low-level steps of the conversion: useful to debug / understand / learn!
• Extra plugins: binary patching made easy with the --file-patch, --vm-patch, --fork-nopper options! (all details below)

Use Cases

Built-in help

$ ./shellnoob.py -h
shellnoob.py [--from-INPUT] (input_file_path | - ) [--to-OUTPUT] [output_file_path | - ]
shellnoob.py -c (prepend a breakpoint (Warning: only few platforms/OS are supported!)
shellnoob.py --64 (64 bits mode, default: 32 bits)
shellnoob.py --intel (intel syntax mode, default: att)
shellnoob.py -q (quite mode)
shellnoob.py -v (or -vv, -vvv)
shellnoob.py --to-strace (compiles it & run strace)
shellnoob.py --to-gdb (compiles it & run gdb & set breakpoint on entrypoint)

Standalone "plugins"
shellnoob.py -i [--to-asm | --to-opcode ] (for interactive mode)
shellnoob.py --get-const <const>
shellnoob.py --get-sysnum <sysnum>
shellnoob.py --get-errno <errno>
shellnoob.py --file-patch <exe_fp> <file_offset> <data> (in hex). (Warning: tested only on x86/x86_64)
shellnoob.py --vm-patch <exe_fp> <vm_address> <data> (in hex). (Warning: tested only on x86/x86_64)
shellnoob.py --fork-nopper <exe_fp> (this nops out the calls to fork(). Warning: tested only on x86/x86_64)

"Installation"
shellnoob.py --install [--force] (this just copies the script in a convinient position)
shellnoob.py --uninstall [--force]

Supported INPUT format: asm, obj, bin, hex, c, shellstorm
Supported OUTPUT format: asm, obj, exe, bin, hex, c, completec, python, bash, ruby, pretty, safeasm
All combinations from INPUT to OUTPUT are supported!

Installation (only if you want)

$ ./shellnoob.py --install

This will just copy the script to /usr/local/bin/snoob. That's it. (Run ./shellnoob.py --uninstall to undo).

Convert shellcode from/to different formats with a uber flexible CLI.

$ snoob --from-asm shell.asm --to-bin shell.bin

Some equivalent alternatives (the tool will try to guess what you want given the file extension..)

$ snoob --from-asm shell.asm --to-bin
$ snoob shell.asm --to-bin
$ snoob shell.asm --to-bin - > shell.bin
$ cat shell.asm | snoob --from-asm - --to-bin - > shell.bin

Formats description

• "asm" - standard assembly. ATT syntax by default, use --intel to use Intel syntax. (see "asm as output" section for more details)
• "bin" - raw binary ('\x41\x42\x43\x44')
• "hex" - raw binary encoded in hex ('41424344')
• "obj" - an ELF
• "exe" - an executable ELF
• "c" - something ready to embed in a C program.
• "python", "bash", "ruby" - same here.
• "completec" - compilable C that properly set the memory as RWX (to support self-modifying shellcodes)
• "safeasm" - assembly that is 100% assemblable: sometimes objdump's output, from which the "asm" is taken, is not assemblable. This will output the "raw" bytes (in .byte notation) so that it's assemblable by "as".
• "shellstorm" - The --from-shellstorm switch takes as argument a <shellcode_id>. ShellNoob will grab the selected shellcode from the shell-storm shellcode DB, and it will convert it to the selected format.

Easy debugging

$ snoob -c shell.asm --to-exe shell
$ gdb -q shell
$ run
Reading symbols from ./shell...(no debugging symbols found)...done.
(gdb) run
Starting program: ./shell

Program received signal SIGTRAP, Trace/breakpoint trap.
0x08048055 in ?? ()
(gdb) 

Or you can use the new --to-strace and --to-gdb switches!

$ snoob open-read-write.asm --to-strace
Converting open-read-write.asm (asm) into /tmp/tmpBaQbzP (exe)
execve("/tmp/tmpBaQbzP", ["/tmp/tmpBaQbzP"], [/* 97 vars */]) = 0
[ Process PID=12237 runs in 32 bit mode. ]
open("/tmp/secret", O_RDONLY)           = 3
read(3, "thesecretisthedolphin\n", 255) = 22
write(1, "thesecretisthedolphin\n", 22thesecretisthedolphin
) = 22
_exit(0)  

$ snoob open-read-write.asm --to-gdb
Converting open-read-write.asm (asm) into /tmp/tmpZdImWw (exe)
Reading symbols from /tmp/tmpZdImWw...(no debugging symbols found)...done.
(gdb) Breakpoint 1 at 0x8048054
(gdb)

Note how ShellNoob automatically sets a breakpoint on the entry point!

Get syscall numbers, constants and errno

$ snoob --get-sysnum read
i386 ~> 3
x86_64 ~> 0
$ snoob --get-sysnum fork
i386 ~> 2
x86_64 ~> 57

$ snoob --get-const O_RDONLY
O_RDONLY ~> 0
$ snoob --get-const O_CREAT
O_CREAT ~> 64
$ snoob --get-const EINVAL
EINVAL ~> 22

$ snoob --get-errno EINVAL
EINVAL ~> Invalid argument
$ snoob --get-errno 22
22 ~> Invalid argument
$ snoob --get-errno EACCES
EACCES ~> Permission denied
$ snoob --get-errno 13
13 ~> Permission denied

Interactive mode

$ ./shellnoob.py -i --to-opcode
asm_to_opcode selected
>> mov %eax, %ebx
mov %eax, %ebx ~> 89c3
>> 

./shellnoob.py -i --to-asm
opcode_to_asm selected
>> 89c3
89c3 ~> mov %eax,%ebx
>>

ShellNoob as a library

$ python
>>> from shellnoob import ShellNoob
>>> sn = ShellNoob(flag_intel=True)

>>> sn.asm_to_hex('nop; mov ebx,eax; xor edx,edx')
'9089c331d2'
>>> sn.hex_to_inss('9089c331d2')
['nop', 'mov ebx,eax', 'xor edx,edx']

>>> sn.do_resolve_syscall('fork')
i386 ~> 2
x86_64 ~> 57