NetRipper - Smart Traffic Sniffing for Penetration Testers

NetRipper is a post exploitation tool targeting Windows systems which uses API hooking in order to intercept network traffic and encryption related functions from a low privileged user, being able to capture both plain-text traffic and encrypted traffic before encryption/after decryption.

NetRipper was released at Defcon 23, Las Vegas, Nevada.


The post-exploitation activities in a penetration test can be challenging if the tester has low-privileges on a fully patched, well configured Windows machine. This work presents a technique for helping the tester to find useful information by sniffing network traffic of the applications on the compromised machine, despite his low-privileged rights. Furthermore, the encrypted traffic is also captured before being sent to the encryption layer, thus all traffic (clear-text and encrypted) can be sniffed. The implementation of this technique is a tool called NetRipper which uses API hooking to do the actions mentioned above and which has been especially designed to be used in penetration tests, but the concept can also be used to monitor network traffic of employees or to analyze a malicious application.

Tested applications

NetRipper should be able to capture network traffic from: Putty, WinSCP, SQL Server Management Studio, Lync (Skype for Business), Microsoft Outlook, Google Chrome, Mozilla Firefox. The list is not limited to these applications but other tools may require special support.

NetRipper.exe - Configures and inject the DLL  
DLL.dll - Injected DLL, hook APIs and save data to files
netripper.rb - Metasploit post-exploitation module

Command line
Injection: NetRipper.exe DLLpath.dll processname.exe  
Example: NetRipper.exe DLL.dll firefox.exe

Generate DLL:

-h, --help Print this help message
-w, --write Full path for the DLL to write the configuration data
-l, --location Full path where to save data files (default TEMP)


-p, --plaintext Capture only plain-text data. E.g. true
-d, --datalimit Limit capture size per request. E.g. 4096
-s, --stringfinder Find specific strings. E.g. user,pass,config

Example: NetRipper.exe -w DLL.dll -l TEMP -p true -d 4096 -s user,pass

Metasploit module
msf > use post/windows/gather/netripper 
msf post(netripper) > show options

Module options (post/windows/gather/netripper):

Name Current Setting Required Description
---- --------------- -------- -----------
DATALIMIT 4096 no The number of bytes to save from requests/responses
DATAPATH TEMP no Where to save files. E.g. C:\Windows\Temp or TEMP
PLAINTEXT true no True to save only plain-text data
PROCESSIDS no Process IDs. E.g. 1244,1256
PROCESSNAMES no Process names. E.g. firefox.exe,chrome.exe
SESSION yes The session to run this module on.
STRINGFINDER user,login,pass,database,config no Search for specific strings in captured data

Metasploit installation (Kali)
  1. cp netripper.rb /usr/share/metasploit-framework/modules/post/windows/gather/netripper.rb
  2. mkdir /usr/share/metasploit-framework/modules/post/windows/gather/netripper
  3. g++ -Wall netripper.cpp -o netripper
  4. cp netripper /usr/share/metasploit-framework/modules/post/windows/gather/netripper/netripper
  5. cd ../Release
  6. cp DLL.dll /usr/share/metasploit-framework/modules/post/windows/gather/netripper/DLL.dll

PowerShell module

@HarmJ0y Added Invoke-NetRipper.ps1 PowerShell implementation of NetRipper.exe

  1. PlainText - Allows to capture only plain-text data
  2. DataLimit - Save only first bytes of requests and responses
  3. Stringinder - Find specific string in network traffic

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