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nxBender

a simple Python client for netExtender VPNs (SonicWALL/Dell)

Supports basic IPv4 connectivity with routing and DNS.

Requirements

You can install the package with:

    pip install .

You will also need pppd.

For manual development, install Python dependencies with:

    pip install -r requirements.txt

Usage

Very simply:

    sudo nxBender --server my-sslvpn-host.com -u username -p password -d domainname

-p password is optional, if not supplied it will ask interactively on the commandline

You can supply the server's SSL certificate fingerprint with --fingerprint if you're using self-signed certificates or if you want pinning.

Options can also be placed into a configuration file - defaulting to /etc/nxbender or ~/.nxbender - such as:

    server = my-sslvpn-host.com
    username = username
    password = password
    fingerprint = 9d:6a:fe:04:78:93:b0:a5:38:a0:04:ac:d2:10:cb:f7:9c:42:cf:74

Portability

At present the VPN routes are set up using pyroute2, which uses Linux's netlink interface to manage routing. A cross-platform approach could use ip and route binaries instead.

The output of pppd is parsed to determine the remote gateway address rather than using the ip-up mechanism, to avoid headaches caused by differences in implementation between distributions (somewhere Dell's client trips up). This might prove fragile, but pppd is very stable nowadays.

Why?

The official client is a pain to use; it only works out of the box on some very specific Linux flavours, has little useful debugging output, and I had to disassemble the binaries to even get it working on Gentoo.

The CLI component also has a number of painful behaviours, including requiring user input to acknowledge self-signed certificates - even when reconnecting during a session - and with no way to store the fingerprint for some reason; so acceptance can be automated with expect but is then vulnerable to MitM. It frequently leaves entries in resolv.conf when the VPN is down, breaking DNS for the entire system.

When I took a peek the protocol was trivial so I spent a couple of hours on a Sunday smashing out a replacement. Thus far it has proven quite reliable.

TODO

Not currently implemented are:

  • IPv6
  • DNS search suffixes
  • auto reconnection
  • configurable timeouts/link loss detection