Threat Level: green Handler on Duty: Didier Stevens

SANS ISC: VPN Access and Activity Monitoring SANS ISC InfoSec Forums

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VPN Access and Activity Monitoring

Because most individuals are going to have to work remotely from home, the activity that should be scrutinized over the coming weeks would be ports associated with VPN like OpenVPN (1194) or SSL VPN (TCP/UDP 443, IPsec/IKEv2 UDP 500/4500) with their associated logs to ensure these services are accessed by the right individuals and are not abused, exploited or compromised. It will be very important the VPN service is patched and up-to-date because there will be way more scrutiny (scanning) against these services. Capturing metrics about performance and availability will be very important to ensure mission critical systems and applications can be accessed to avoid downtime.

Some difficult questions will need to be answers:

How many concurrent users can login at the same time?
Will the vpn corporate policy be relaxed to accommodate the maximum of employees?
Who gets priority access if the appliance or service cannot support everyone?
How much bandwidth a typical user use?
Do you split access time between users (i.e. each gets 2 hours)?
Number of VPN license or MFA token available
Are users allowed to use the personal computer?
If personal computers are allowed:

  • What is their security posture (patches, AV update, etc)?
  • Can they be trusted?
  • What files or shares are employees allowed to access?

What are the alternative?


Guy Bruneau IPSS Inc.
My Handler Page
Twitter: GuyBruneau
gbruneau at isc dot sans dot edu


511 Posts
ISC Handler
Mar 15th 2020
Some additional website to check:

From SANS Security Awareness:…
From US-CERT on Enterprise VPN Security:…

511 Posts
ISC Handler
I ran into trouble with session affinity not being respected because of UDP vs TCP, so if you're doing online conferencing then switch to TCP to ensure your sessions don't break.

Also be careful mixing VPNs simultaneously in case VPN A's addressing overlaps with VPN B's etc..

If you're an expert user, then boost performance/UX/privacy by running your own recursive DNS server locally like Unbound over DoT/DoH.


1 Posts
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