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dynvpn

dynVPN is a set of small python programs for dynamicaly applying firewall profiles to users. Based on group memberships when connecting to the VPN server. This proves quite usefull to get a more "enterprisey VPN" creating narrow and unique access controls for each type of connecting user.

Requirements:

Check Dockerfile

How to start the POC:

docker build -t dynvpn 
docker run -ti --privileged -p 1194:1194/udp  -v dynvpn:/etc/openvpn/easy-rsa/keys dynvpn
VOL_PATH=/var/lib/docker/volumes/dynvpn/_data/
openvpn --config $VOL_PATH/client-vpn.conf --cd $VOL_PATH 

you can inspect the dynamic ruleset applied from within the container with:

nft list ruleset

to see that explicit allow rules has been added to a custom chain for your connected vpn user

Openvpn client connection state transition

  1. User connects to VPN and auths
  2. After authentication the cn (common name taken from the certificate file generated for vpn client certificate holder) is checked against the acl_members file where for each group a user belongs to (for example group2 group1 ) the learn_adress script will execute a file called group2.py applying that set of nftables rules for the unique ip the user is connected to the OpenVPN server with.
  3. User disconnects User disconnection is handled by a ping time out set in server.conf. When time out is reached the connection is dropped causing OpenVPN to call the learn-address hook with the delete action Dropping the VPN connection and removing firewall rules for that VPN session.

Python program files overview

  • learn_address

Is the hook script called when a a vpn session is established
It allows openvpn to launch a custom program when openvpn learns of a new adress of a connecting user. In our scenario the program calls learn_address doing step 3-4 described above the learn adress hook in OpenVPN sends three variables to the script: Action, IP, User where an action can be:

  • add - when a new connection is established
  • delete - when a connection is reported as disconnected (se #4 above)
  • update - when a connection is updates usually when there is a new ip. We do a DELETE/ADD when this happens

learn_Address be called from the shell to testing the firewall actions:

./learn_address ACTION IP USERNAME
  • globs.py

contains global variables and paths to files for the program learn adress and manage_acl_users It also has a debug flag that can be flipped to increase logging

  • acl_members

This file contains the mapping between users and groups where user is the auth name for openvpn. Each group is referencing a python file containing firewall rules users group information stored in the following format:

john_doe allow_ssh allow_dns jane_doe allow_ntp ...

  • acl_rules/

This folder is where ACL rules are kept and searched for when a user is to be mapped to a group. Path to it is specified in globs.py has to include the python magic in the begining of file check any file except for the template_rule.py for an example

  • acl_rules/template_rule.py

this is a base template that should be included in your custom acl files doing some generic tasks that happen in each rule file

  • /etc/openvpn/scripts/sessions/

Ddestination folder for session files a file for each currently connected user stating the ip, username and applied rules for a connected user

How the VPN scripts interacts with networking and firewalling

For traffic to pass from the OpenVPN client into our networks it first has to auth (check #1 further info). After auth openvpn pushes some explicit routes for our network declared in server.conf

Traffic from a connected vpn client will reach FORWARDING table on the vpn server. The default policy for the forwarding table should be set to drop all traffic. Meaning that only traffic matching the explicit ALLOW rules in the rules mapped to a user will be allowed to pass

The acl_rules/ contains rule files that are applied to mapped users. For each connecting user a jump reference is created in the forwarding table for the users connecting IP in this table each acl rule files rules will be applied

TODO

  • rewrite for python3
  • tests
  • rewrite acl_members and management of file in some more easily parsable format like json or yaml
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