Author: David Zimmer
Date: 01.21.11 - 5:27am
scdbg is a shellcode analysis application built around the libemu emulation library. When run it will display to the user all of the Windows API the shellcode attempts to call.
What I wanted was a emulation version of sclog that I could be free to run without worry on my dekstop.
140+ new api hooks, 9 new dlls, interactive debug shell, rebuilt PEB, support for file format exploits, support for return address scanners, memory monitor, report mode, dump mode, easily human readable outputs, log after xx capabilities, directory mode, inline analysis of process injection shellcode and more...
here log after step option (-las) shows exactly why shellcode is crashing:
it is trying to execute 2nd stage shellcode from stack loaded with a recv.
This shellcode could be run further with the -i interactive mode option.
The simplest command line you can use is:
Where shellcode_file.sc is the raw shellcode in binary format.
- scdbg -f shellcode_file.sc
An example of working with shellcode for a file format exploit might look like:
In this case, the shellcode can scan for the open file handle, and actually decode and extract the embedded executables dropping them to disk for you.
- scdbg -f shellcode.sc -fopen bad.doc_ -s -1 -i
Docs & Resources:
For Windows Users I have ported the library over to give a native compile using Visual Studio 2008. This is the main development branch going forward.
Linux users should grab the GCC source below which can still be cross compiled. (Windows cygwin users may also be interested in the GCC builds as they still contain the graphing and original -getpc features)
The Visual Studio source repository also includes several other sub projects such as tool to create -patch files as well as project to compile as __stdcall DLL. This libemu dll is suitable for use with Visual Basic 6, C Sharp any other language which can consume a standard Windows dll. Example projects are available in the languages mentioned above.
Windows Native Source/Binaries (15 dlls, 242 hooks - current development branch)
*nix/Cygwin Source/Binaries (100 hooks - inactive)
The older gcc compatible and cross-compilable version is available here:
(tested with cygwin/gcc 3.4 & 4.3, RHEL 2.6/ gcc 4.1)
Thanks again to Markus and Paul for releasing this very cool library!
Help screen below: (see scdbg -h for current options)
scdbg is an adaption of the libemu library and sctest project
Libemu Copyright (C) 2007 Paul Baecher & Markus Koetter
scdbg developer: David Zimmer
Compile date: Apr 14 2011 21:02:02
/foff hexnum starts execution at file offset
/mm enabled Memory Monitor (logs access to key addresses)
/mdll Monitor Dll - log direct access to dll memory (hook detection/patches)
/nc no color (if using sending output to other apps)
/f fpath load shellcode from file specified.
/o hexnum base offset to use (default: 0x401000)
/redir ip:port redirect connect to ip (port optional)
/i enable interactive hooks
/v verbosity, can be used up to 4 times, ex. /v /v /vv
/e int verbosity on error (3 = debug shell)
/t int time to delay (ms) between steps when v=1 or 2
/h show this help
/ba hexnum break above - breaks if eip > hexnum
/bp hexnum set breakpoint on addr or api name (same as -laa -vvv)
/bs int break on step (shortcut for -las -vvv)
/a adjust offsets to file offsets not virtual
/d dump unpacked shellcode (requires /f)
/las int log at step ex. -las 100
/laa hexnum log at address or api ex. -laa 0x401020 or -laa ReadFile
/s int max number of steps to run (def=2000000, -1 unlimited)
/hex show hex dumps for hook reads/writes
/findsc detect possible shellcode buffers (brute force)
/dump view hexdump of the target file (can be used with /foff)
/disasm int Disasm int lines (can be used with /foff)
/fopen file Opens a handle to for use with GetFileSize() scanners
/- /+ increments or decrements GetFileSize, can use multiple times
/hooks dumps a list all implemented api hooks
/r show analysis report at end of run
/pp peb patch - required for some shellcodes (rare)
/b0 break if 00 00 add [eax],al
/patch fpath load patch file for libemu memory
/dir folder process all .sc files in echo results to .txt
dbg> shell prompt commands:
? - help, this help screen, h also works
v - change verbosity (0-4)
g - go - continue with v=0
s - step, continues execution, ENTER also works
c - reset step counter
r - execute till return (v=0 recommended)
u - unassembled address
b - break at address
m - reset max step count (-1 = infinate)
e - set eip
w - dWord dump,(32bit ints) prompted for hex base addr and then size
d - Dump Memory (hex dump) prompted for hex base addr and then size
x - execute x steps (use with reset step count)
t - set time delay (ms) for verbosity level 1/2
k - show stack
i - break at instruction (scans disasm for next string match)
f - dereF registers (show any common api addresses in regs)
o - step over
.lp - lookup - get symbol for address
.pl - reverse lookup - get address for symbol
.seh - shows current value at fs
.reg - manually set register value
.poke1 - write a single byte to memory
.poke4 - write a 4 byte value to memory
.savemem - saves a memdump of specified range to file
q - quit