scdbg download


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.
Additions include:
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:
  • scdbg -f shellcode_file.sc
Where shellcode_file.sc is the raw shellcode in binary format.

An example of working with shellcode for a file format exploit might look like:
  • scdbg -f shellcode.sc -fopen bad.doc_ -s -1 -i
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.

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, 297 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: Oct 16 2019 19:41:30

  /f fpath              load shellcode from file - accepts binary, %u, x, %x, hex blob
  /api                  scan memory and try to find API table
  /auto                 running as part of an automation run
  /ba hexnum            break above - breaks if eip > hexnum
  /bp varies            set breakpoint on file offset, virtual addr or api name (max 10)
  /bs int               break on step (shortcut for -las  -vvv)
  /b0                   break if 00 00 add [eax],al
  /cmd "string data"    data to use for GetCommandLineA (use " to embed quotes)
  /cfo                  CreateFileOverRide - if /fopen use handle else open real arg
  /d                    dump unpacked shellcode
  /dir  folder          process *.sc in  supports: -r (1 report), -v (report mode), -u
  /disasm int           Disasm int lines (can be used with /foff)
  /dump                 view hexdump (can be used with /foff)
  /e int                verbosity on error (3 = debug shell)
  /findsc               detect possible shellcode buffers (brute force) (supports -dump, -disasm)
  /fopen file           Opens a handle to  for use with GetFileSize() scanners
  /foff hexnum          starts execution at file offset (also supports virtual addresses)
  /h                    show this help
  /hex                  show hex dumps for hook reads/writes (paged)
  /hooks                dumps a list all implemented api hooks
  /i                    enable interactive hooks (file and network)
  /las int              log at step ex. -las 100
  /laa hexnum           log at address or api ex. -laa 0x401020 or -laa ReadFile
  /lookup api           shows the address of WinAPi function ex. -lookup GetProcAddress
  /mm                   enabled Memory Monitor (logs access to key addresses)
  /mdll                 Monitor Dll - log direct access to dll memory (hook detection/patches)
  /min steps            min number of steps (decimal) to trigger record in findsc mode (def 200)
  /nc                   no color (if using sending output to other apps)
  /noseh                Disables support for seh and UnhandledExceptionFilter
  /norw                 Disables display of read/write file hooks
  /o hexnum             base offset to use (default: 0x401000)
  /patch fpath          load patch file  into libemu memory
  /pad 0xVal            add an extra 0xVal bytes to shellcode
  /r                    show analysis report at end of run (includes -mm)
  /redir ip:port        redirect connect to ip (port optional)
  /s int                max number of steps to run (def=2000000, -1 unlimited)
  /sigs                 show signatures (can be used with -disasm)
  /t int                MS to delay between steps (v1-2) or api (v0)
  /temp folder          use folder as temp path for interactive mode file writes
  /u                    unlimited steps (same as -s -1)
  /v                    verbosity, can be used up to 4 times, ex. /v /v /vv
  /- /+                 increments or decrements GetFileSize, can be used multiple times
  /va 0xBase-0xSize     VirtualAlloc memory at 0xBase of 0xSize
  /raw 0xBase-fpath     Raw Patch Mode: load fpath into mem at 0xBase (not PE aware)
  /llo dllName-0xBase   LoadLibrary Override: returns 0xBase for LoadLibrary/GetModuleHandle
  /wbyte 0xBase-0xVal   Write 8bit 0xValue at 0xBase (/wb shortcut supported)
  /wint 0xBase-0xVal    Write 32bit integer 0xValue at 0xBase
  /wstr 0xBase-Str      Write string at base ex. 0x401000-0x9090EB15CCBB or "0xBase-ascii string"
  /dllmap               show the name, base, size, and version of all built in dlls
  /nofile               assumes you have loaded shellcode manually with -raw, -wstr, or -wint
  /bswap                byte swaps -f and -wstr input buffers
  /eswap                endian swaps -f and -wstr input buffers
  /xor 0xVal            xor -f and -wstr input buffers with 1 - 4 byte keys
  /conv path            outputs converted shellcode to file (%u,x,bswap,eswap..)
  /ida                  connects to last opened IDA instance on startup
  /[reg] value          sets init register value ex: -eax 0x20 -ebx 20 -ecx base -reg base

   dbg>
        ? - 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 x instructions at address (default eip)
        b - sets next free breakpoint (10 max)
        m - reset max step count (-1 = infinate)
        e - set eip (file offset or VA)
        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)
        j - show log of last 10 instructions executed
        o - step over
        ; - Set comment in IDA if .idasync active
        +/- - basic calculator to add or subtract 2 hex values
        .bl - list set breakpoints
        .bc - clear breakpoint
        .api - scan memory for api table
        .nop - nops out instruction at address (default eip)
        .seh - shows current value at fs[0]
        .segs - show values of segment registers
        .skip - skips current instruction and goes to next
        .reg - manually set register value
        .dllmap - show dll map
        .poke1 - write a single byte to memory
        .poke4 - write a 4 byte value to memory
        .lookup - get symbol for address
        .symbol - get address for symbol (special: peb,dllmap,fs0)
        .savemem - saves a memdump of specified range to file
        .idasync - connect IDASrvr plugin and sync view at step or break.
        .allocs - list memory allocations made
        q - quit







Comments: (3)

On 01.23.16 - 3:47pm Dave wrote:
Note that the windows version of scdbg.exe looks to run ok under wine. the gui_launcher.exe however will not.

On 10.18.17 - 5:44am Dave wrote:
if you hit a shellcode that has a legit opcode not supported you can try it against the scdbg unicorn build which has merged the libemu Win32 env with the Unicorn (QEMU) emulator. All the hooks are in place and working, but I have not ported all of the command line options over yet.

You can read more about how this was done in my Writing a libemu/Unicorn Compatability Layer Fireeye blog post.

On 10.16.19 - 8:19am Gabor Szappanos wrote:
Thank you for maintaining scdbg, it is an extremely useful tool. The hook of ZwSetInformationProcess contains a bug. This line if(infoClass0x22){ I believe should be if(infoClass0x22){

 
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