vpnnotify

vpnnotify is a tool that will send a user a slack message when they connect to a VPN session. The goal of this tool is to let people know when connections are initiated on their behalf -- with the goal being that if a connection occurs without the user knowing, they could contact their CIRT.

vpnnotify builds off of the support OpenVPN has for a client connect script. This script will run when a client successfully connects to the VPN. OpenVPN exposes several environment variables for the script it runs to use. The ones vpnnotify currently uses are common_name (the login name) and untrusted_ip (the IP of the connection).

There are many improvements that could be made to vpnnotify -- as it is, we know that this is fairly environment specific. We open sourced in hopes that we could help level up other security operations teams and make another tool that would contribute to the community.

Prerequisites

In order to use vpnnotify you'll need to have the following:

• LDAP server with the slackUser object class
• Redis to store last logged in state
• OpenVPN - we've tested with 2.3.12 and later
• FQDNs that have either dev or prod in them as an indicator of environment

slackUser Object Class

This adds a SlackName attribute to a record. If you use OpenLDAP with LDIF configuration, this schema LDIF will work:

dn: cn=slackuser,cn=schema,cn=config
objectClass: olcSchemaConfig
cn: slackuser
olcAttributeTypes: ( 1.3.6.1.4.1.48697.1.2.1.3.1 NAME 'slackName' DESC 'Slack
  at-name' EQUALITY caseIgnoreMatch SUBSTR caseIgnoreSubstringsMatch
  SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 SINGLE-VALUE)
olcObjectClasses: ( 1.3.6.1.4.1.48697.1.2.1.4.1 NAME 'slackUser' DESC 'Slack
  User' SUP top AUXILIARY MUST (slackName) )

Building and Installing

Building vpnnotify is as easy as running go build. You could use FPM to make it into a package that could install to /usr/bin, if you wanted.

Configuration

vpnnotify uses a configuration file which is, by default, in /etc/vpnnotify.json. You can override this with the VPNNOTIFY_CONFIG environment variable.

Example Configuration

Here's a sample configuration file:

{
  "GeoIPEnabled": true,
  "GeoIPPath": "/opt/GeoLite2-City_20170502/GeoLite2-City.mmdb",
  "LDAPBaseDN": "dc=cool,dc=io",
  "LDAPPort": 389,
  "LDAPServer": "ldap.cool.io",
  "LDAPSkipVerify": false,
  "LDAPUserAttrib": "uid",
  "RedisDB": 0,
  "RedisPassword": "seCretsRc00l",
  "RedisPort": 6379,
  "RedisServer": "redis.cool.io",
  "RedisTLS": true,
  "RenotifyTime": 7200,
  "SlackKey": "xozz-blah-moreblah",
  "TemplatePath": "/etc/vpnnotify.msg"
}

Configuration Attributes

Variable	Type	Purpose	Possible Value
GeoIPEnabled	Bool	Whether to use GeoIP. Consult their license terms.	true, false
GeoIPPath	String	Path to the GeoIP MMDB file	/opt/cooldb.mmdb
LDAPBaseDN	String	Base DN for your LDAP server	dc=cool,dc=io
LDAPPort	Int	Port for the LDAP server (must use StartTLS)	389
LDAPServer	String	FQDN for LDAP server (must use StartTLS)	ldap.cool.io
LDAPSkipVerify	Bool	Whether to check the TLS certificate (for testing only!)	false (you should keep it false)
LDAPUserAttrib	String	The attribute by which to look up users	uid
RedisDB	Int	The database number to use	0
RedisPassword	String	A password for Redis	secret
RedisPort	Int	A port for Redis	6379
RedisServer	String	FQDN for the Redis Server	redis.cool.io
RedisTLS	Bool	Attempt to talk to Redis using TLS	true, false
RenotifyTime	Int	Number of seconds to not renotify a user if from same IP	7200
SlackKey	String	The key for Slack	xozz-...
TemplatePath	String	A path to a go template file	/etc/vpnnotify.msg

The Template

This is where you actually put the message that will be sent via Slack. Here's a sample message template:

You just started a VPN session into *{{.Env}}* from {{.IP}}{{if eq .GeoIP true}} ({{if ne .City ""}}{{.City}}, {{end}}{{if ne .State ""}}{{.State}},{{end}}{{if ne .Country ""}} {{.Country}}{{end}}){{end}}. If this wasn't you, please reach out to ops immediately.

There aren't a lot of variables to use in the template. Here's what is available right now:

Variable	Type	Purpose
Env	String	The environment the person logged into (dev/prod/???)
IP	String	The connecting IP address
GeoIP	Bool	If GeoIP is enabled
City	String	GeoIP: City
Country	String	GeoIP: Country
State	String	GeoIP: State or other municipal division

Configuring OpenVPN

Set client-connect = /path/to/vpnnotify in your OpenVPN config. That's it.

Testing

You can run vpnnotify locally. On the command line, run VPNNOTIFY_CONFIG=./vpnnotify.json common_name=username untrusted_ip=8.8.8.8 ./vpnnotify which will simulate username logging into the VPN from 8.8.8.8.

When you test, you may want to set RenotifyTime shorter, depending on what you're testing.

Contributing

There are a few things we know could use some improvement:

• We currently infer environment based on the OpenVPN host's hostname - maybe this should be done via the configuration file? (ideal for first time contributors!)
• We alert on the positive condition (known user successfully connects). What about users who don't have the slackUser attribute? Are there other negative conditions we're missing?
• vpnnotify is fairly unsophisticated. Some statistical analysis would be extremely helpful in dialing down "alert fatigue" with the caveat that any statistical analysis should not require too much "extra" to run

We're open to pull requests, and we're looking forward to reading yours!