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June 27, 2017 12:53
June 26, 2020 13:08
June 27, 2017 12:53
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June 27, 2017 12:53
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June 27, 2017 12:53
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FENRIR is a tool designed to be used "out-of-the-box" for penetration tests and offensive engagements. Its main feature and purpose is to bypass wired 802.1x protection and to give you an access to the target network.

Keep in mind FENRIR is still a Work in Progress

Branches :

  • master : main branch for (relatively) stable code
  • bleeding : branch with hotfixes and latest updates


FENRIR must be ran as root and you must have 2 network interfaces if you want it to work Also, check that both network interfaces are in promisc mode and that ip_forwarding is enabled (see Install section)

To run it :

sudo python

Notice that FENRIR's interface supports autocompletion

You can run shell commands with "!"

!ls -la

You first have to create a virtual tap for FENRIR with :


Then you can either configure it manually or start autoconfiguration :

set <option> <value>

Once FENRIR is configured you can run it normally or in debug mode


The wiki pages are coming shortly with examples and better explanations !


Are you interfaces in promisc mode ? Even FENRIR's tap interface ?
You external interfaces must not have an IP address, only the tap hsould have one
Your default route should be pointing to the tap interface
Have you enabled ip_forwarding ?
FENRIR will tell you if it is lacking configuration. It must have at least the legitimate host IP and MAC addresses.
Not all protocols are currently supported ! But feel free to help the project by creating a module !
If you have found a bug, report it to me ! I'll look at it as quickly as i can.


  • I suck at naming stuff & especially function names
  • The code is always a work-in-progress, there are bugs and weird stuffs ! Feel free to throw bug tickets & pull requests
  • Java sucks

Current and planned features

Specific protocol modules have their own separate table below !

Feature Current state Details
802.1x tapping and bypass Done N/A
Stealth Partially Done Other specific headers L2/L3 are to be added
Autoconfiguration Done N/A
Reverse connections capabilities Done Currently being reworked
Port translation TODO Collision issue avoidance
Runtime interface Done N/A
Better stats TODO
Bug smashing Doing Bugs, bugs everywhere
Code cleaning Doing  It needs it badly !
Not developed in Java Done !!! 'Cause we all know Java sucks right ? :)

Protocol modules table

Protocol Current state Details
IP Done (FENRIR Core) N/A
ARP Done N/A
LLMNR/NBNS (Responder) Partially Done Need to push it inside a separate module
 SSH TBD Need to figure out key exchange rewritting
SMB TBD Next thing on my ToDo list !
??? ??? ???


  • apt-get update
  • apt-get upgrade
  • apt-get install python-pip
  • apt-get install build-essential
  • apt-get install python-dev
  • pip install python-pytun
  • pip install scapy
  • pip install Cmd2
  • git clone this repo

Important note on install

It seems that with the arrival of Python3 some prerequisite packages are now bugged. For now, to avoid bugs while we migrate this tool to Python3, one should remove any files from the following packages and install them like this:

  • sudo -H -E pip install "cmd2<=0.7.0"
  • sudo -H -E pip install "scapy<=2.3.2"

For running FENRIR

  • sysctl net.ipv4.ip_forward=1
  • ifconfig iface1 promisc
  • ifconfig iface2 promisc

If you have any problem with installation, shoot me an email ! I can probably help you out !

Have a beer and participate !

The project is open for pull requests and bug reports ! The great thing is I would be more than happy to offer you a beer for any form of contribution. Please participate in this project and help me make it better :)
And if you don't know where to start or want some help, do not hesitate to contact me !

Also, if you want to chat about the project or ask questions, you can find me on IRC : WaffleWrath

Docs & Vids

My presentation of 802.1x bypass techniques and FENRIR are available on the Hack in Paris website


This software is licensed under the terms of the MIT license

by Valérian Legrand (main developer), Andrei Dumitrescu and Quentin Biguenet (contributors)


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