Add/Sub Encoder - Metasploit


This page contains detailed information about how to use the encoder/x86/add_sub metasploit module. For list of all metasploit modules, visit the Metasploit Module Library.

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Module Overview

Name: Add/Sub Encoder
Module: encoder/x86/add_sub
Source code: modules/encoders/x86/add_sub.rb
Disclosure date: -
Last modification time: 2017-07-24 06:26:21 +0000
Supported architecture(s): x86
Supported platform(s): All
Target service / protocol: -
Target network port(s): -
List of CVEs: -

Encodes payload with add or sub instructions. This idea came from (offensive-security) muts' hp nnm 7.5.1 exploit.

Module Ranking and Traits

Module Ranking:

  • manual: The exploit is unstable or difficult to exploit and is basically a DoS. This ranking is also used when the module has no use unless specifically configured by the user (e.g.: exploit/windows/smb/psexec). More information about ranking can be found here.

Basic Usage

msf > use encoder/x86/add_sub
msf encoder(add_sub) > show targets
    ... a list of targets ...
msf encoder(add_sub) > set TARGET target-id
msf encoder(add_sub) > show options
    ... show and set options ...
msf encoder(add_sub) > exploit

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Msfconsole Usage

Here is how the encoder/x86/add_sub module looks in the msfconsole:

msf6 > use encoder/x86/add_sub

msf6 encoder(x86/add_sub) > show info

       Name: Add/Sub Encoder
     Module: encoder/x86/add_sub
   Platform: All
       Arch: x86
       Rank: Manual

Provided by:
  Melih Sarica <[email protected]>

Description:
  Encodes payload with add or sub instructions. This idea came from 
  (offensive-security) muts' hp nnm 7.5.1 exploit.

Module Options

This is a complete list of options available in the encoder/x86/add_sub module:

msf6 encoder(x86/add_sub) > show options

Module options (encoder/x86/add_sub):

   Name  Current Setting  Required  Description
   ----  ---------------  --------  -----------

Advanced Options

Here is a complete list of advanced options supported by the encoder/x86/add_sub module:

msf6 encoder(x86/add_sub) > show advanced

Module advanced options (encoder/x86/add_sub):

   Name       Current Setting  Required  Description
   ----       ---------------  --------  -----------
   VERBOSE    false            no        Enable detailed status messages
   WORKSPACE                   no        Specify the workspace for this module

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Error Messages

This module may fail with the following error messages:

Error Messages

Check for the possible causes from the code snippets below found in the module source code. This can often times help in identifying the root cause of the problem.

Bad character list includes essential characters.

Here is a relevant code snippet related to the "Bad character list includes essential characters." error message:

94:	    end
95:	    offset = (datastore['BufferOffset'] || 0).to_i
96:	    @inst = {}
97:	    @set = add_or_sub(@avchars)
98:	    if @set == 0 then
99:	      raise EncodingError, "Bad character list includes essential characters."
100:	      exit
101:	    elsif @set == 1 then #add
102:	      @inst["opcode"] = 0x05
103:	    else #sub
104:	      @inst["opcode"] = 0x2d

Shellcode size must be divisible by 4, try nop padding.

Here is a relevant code snippet related to the "Shellcode size must be divisible by 4, try nop padding." error message:

107:	    @inst["pop"] = 0x58
108:	    @inst["and"] = 0x25
109:	    @inst["push_esp"] = 0x54
110:	    @inst["pop_esp"] = 0x5c
111:	    if state.buf.size%4 != 0 then
112:	      raise EncodingError, "Shellcode size must be divisible by 4, try nop padding."
113:	      exit
114:	    end
115:	    #init
116:	    write_inst(@inst["push_esp"], 0)
117:	    write_inst(@inst["pop"], 0)

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See Also

Check also the following modules related to this module:

Authors

Melih Sarica <ms[at]sevure.com>

Version

This page has been produced using Metasploit Framework version 6.1.24-dev. For more modules, visit the Metasploit Module Library.

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