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Co-authored by James Robinson and Jeff Kessler
As rapidly as wide-area networking (WAN) and remote access strategies with associated technologies are changing, we’re always surprised by the amount of time some security professionals and auditors dedicate to the either/or debate between split tunnel and full tunnel connectivity.
History can partially explain how we got here. Long before COVID-19 reared its ugly head, corporate security teams were already grappling with how best to protect remote connectivity. First, they directed all employees working remotely to reach the corporate network via VPN, which meant all traffic was routed through the firewall/VPN concentrator in the enterprise data center. When these users were only, or primarily, accessing applications housed inside the corporate network, that made sense, although bandwidth limitations sometimes reduced application performance. A middle ground many of us found (we liked to call it splint-tunneling) was also to enable direct connections for “approved” cloud services while everything else was sent to the data center. However, this approach still had weaknesses including the abuse of these exposed cloud services and the lack of visibility by security teams. As cloud solutions became more and more prevalent, forcing traffic traveling from remote offices to cloud-based applications (and vice versa) to make a pitstop in the data center began to make less and less sense.
The easy solution was to reduce unnecessary backhauling to the data center by letting remote machines talk directly to the internet. Many security teams implemented “split tunneling,” by which traffic that needs to pass through the corporate network utilizes VPN connections, while traffic that is headed to the internet goes there directly without visiting the data center at all.
But easy is not security and split tunneling raises massive red flags for security teams. Internet browsers, software-as-a-service (SaaS) applications, and streaming technologies create new attack vectors for malware. Unless these solutions’ data streams flow through the corporate firewall, the company is relying solely on endpoint protection solutions for threat detection and mitigation. If a DNS or ICMP attack were to succeed in bypassing endpoint security, not only could it be used as a covert channel, but it could also be the entry point to the enterprise over the VPN connection. Historically security teams have not had good visibility into these kinds of attacks where the command and control traffic is asynchronous to the tunneled traffic that goes into the enterprise. Furthermore, these split-tunneled systems were mini-pivot points allowing the compromise of a system to be entry into data center secured systems and applications.
Split tunneling was already problematic and controversial before COVID. It was hard to manage the complexity of source to destination ports and protocols resulting in many companies using an all or none approach to accessing systems/apps or requiring jump boxes and other technologies to be offered up for end-users. Then the pandemic hit, leading businesses around the world to send large portions of their workforce home. And for companies that were still relying on full tunnel connectivity a year ago, backhauling all traffic through the data center, the sudden COVID-driven leap in traffic volume slowed performance to a crawl for WAN end users. Scalability was also hard to measure for the unexpected increase in volume. This rush for procuring and implementing additional infrastructure to support the increased volume of traffic didn’t allow for much time to secure, harden, and monitor this new infrastructure.
Secure multipoint tunneling offers another option
What, then, is a security team to do when Microsoft 365, Google Workspace, and even teleconferencing applications like Zoom underpin almost every facet of corporate operations? Should security leaders insist on VPN backhauling, adding latency that may undermine employee productivity? Should they use PAC files and other technologies which add complexity and have complex models for management? Or should they eliminate filtering on internet traffic, with all the dangers that approach entails?
My answer, as a security leader who’s been tested plenty, is neither of the above. Instead, security teams should expand their horizons and consider a third solution to the dilemma—secure multipoint tunneling. It’s a model of network architecture in which remote traffic enters the corporate network only if the data center is its final destination. But unlike split tunneling, secure multipoint tunneling does not leave other traffic unprotected. As the name implies, secure multipoint tunneling routes communications to and from cloud-based resources through a second tunnel, which is protected by a cloud firewall.