Running Cisco AnyConnect VPN on a Headless Machine


Running Cisco AnyConnect VPN on a headless Linux machine is no fun:

$ /opt/cisco/anyconnect/bin/vpn connect vpn.example.com
[..]

> VPN establishment capability for a remote user is disabled.  A VPN
> connection will not be established.

You'll get the same problem on a local machine with a graphical display/X if you've got another user logged in from one of the TTY consoles. E.g. here root is logged in from tty1 after first doing Ctrl + Alt + 1:

$ w
 19:55:49 up  4:02,  5 users,  load average: 0.00, 0.04, 0.19
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
torstein tty7     :0               08:22    5:06m  1:14   1.48s /usr/bin/i3
root     tty1     -                13:28   28.00s  0.10s  0.09s -zsh

Even though there's no remote user on this machine, both users are local, Cisco AnyConnect will refuse to connect to the VPN server

The reason is that the VPN client downloads a profile XML file from the VPN server and that profile contains these lines:

<WindowsVPNEstablishment>LocalUsersOnly</WindowsVPNEstablishment>
<LinuxVPNEstablishment>LocalUsersOnly</LinuxVPNEstablishment>

What you want is:

<LinuxVPNEstablishment>AllowRemoteUsers</LinuxVPNEstablishment>

However, if you change the file, it'll get overwritten by the AnyConnect VPN process.

Furthermore, you cannot make the file immutable:

# chattr +i /opt/cisco/anyconnect/profile/AnyC-Profile.xml

As it'll then complain that it cannot connect to the server (happens after you've successfully authenticated with the gateway).

The solution is threefold:

1/3 - Create new AnyConnect profile that works on a headless machine

First, create a version of the AnyConnect profile XML that you get from the VPN gateway, on my system, this is /opt/cisco/anyconnect/profile/AnyC-Profile.xml and create a version of it that allows remote users to create connections:

$ sed 's#LocalUsersOnly#AllowRemoteUsers#g' \
  /opt/cisco/anyconnect/profile/AnyC-Profile.xml \
  > /opt/cisco/anyconnect/profile/AnyC-Profile.xml.foo

2/3 - Ensure this new AnyConnect profile is being used

Before starting your VPN connection, copy your modified of the VPN profile. Then, listen for file system changes in this directory and copy the file over whenever the VPN server tries to overwrite your modified VPN profile:

# cp -v /opt/cisco/anyconnect/profile/AnyC-Profile.xml{.foo,};
  inotifywait \
    -q \
    -m \
    -e close_write \
    -r  /opt/cisco/anyconnect/profile/
  | while read f; do
    cp -v /opt/cisco/anyconnect/profile/AnyC-Profile.xml{.foo,};
  done 

3/3 - Start the VPN connection as normal

$ /opt/cisco/anyconnect/bin/vpn connect vpn.example.com

That's it. You should now be able to start the Cisco VPN on a headless machine, like you can with all other VPN I've worked with the last 20 years.

Happy secure surfing!


Licensed under CC BY Creative Commons License ~ ✉ torstein.k.johansen @ gmail ~ 🐦 @torsteinkrause ~