Bluechip Computer Systems LLC, Recent ransomware attacks like Wanna and Petya have spread largely
unchecked through corporate networks in recent months, extorting money to
restore your data and regain control of your computers. Modern firewalls are
purpose-built to defend against these kinds of attacks, but they need to be
given an opportunity to do their job. In this whitepaper we’ll discuss how these
attacks work, how they can be stopped, and best practices for configuring your
firewall and network to give you the best protection possible.

How Recent Ransomware Attacks Spread

Wanna, Petya, and other ransomware attacks have crippled countless organizations.
Together, these two attacks have infected hundreds of thousands of computers all around
the globe. These particular attacks spread by exploiting a vulnerability in Microsoft’s Server
Message Block (SMB) network file-sharing protocol. This protocol is ubiquitous on corporate
LANs and allows computers to discover each other for the purpose of sharing files and other
resources like printers. It can also be used for file sharing outside the firewall if the necessary
ports (TCP 139 and/or 445) are opened or forwarded on the firewall.
The particular exploit used by Wanna and Petya is known as EternalBlue. EternalBlue allows
remote code execution by sending carefully crafted messages across the network to the
vulnerable SMB service on computers running Microsoft Windows.
In general, every networked system, whether it’s running Windows, Linux, Mac OS, or
some other operating system, relies on a variety of services for network functionality,
and occasionally new vulnerabilities are discovered in these services that can have dire
consequences if maliciously exploited.

In the case of the EternalBlue exploit, Microsoft quickly issued a patch for this vulnerability
once it was publicized, but hackers took advantage of the fact that rolling out patches in
organizations is a considerable undertaking and were able to launch these attacks before
many systems had been updated.

Even in the most diligent organizations, there’s always a gap between vulnerability discovery
and patch deployment, which is why it’s so important to have leading next-gen technology
protecting your network and endpoints from these kinds of attacks.
So how can you protect your organization from letting these attacks into the network in the
first place? And if an attack should somehow penetrate your network, how can you prevent it
from propagating or moving laterally, infecting other systems in its wake?

Blocking Network Exploits

IPS (Intrusion Prevention System) is a critical security component of any next-gen firewall
as it performs deep packet inspection of network traffic to identify vulnerability exploits and
block them before they reach a target host. IPS looks for patterns or anomalies in the code
that either match a specific exploit or a broader target vulnerability.

As with the EternalBlue exploit discussed earlier, these attacks typically attempt to send
malicious inputs to a host application or service to compromise it and gain some level of
control to ultimately execute code – such as a ransomware payload in the case of Wanna
and Petya.

Firewall Best Practices to Block Ransomware Attacks like Wanna and Petya
A Sophos Whitepaper July 2017

Blocking File-Based Ransomware Payloads

While Wanna and Petya spread like worms, many ransomware variants leverage social
engineering tricks through phishing email attacks, spam, or web downloads to gain
entry to your network through more conventional means. These attacks often start as
cleverly crafted malware lurking in common files like Microsoft Office documents, PDFs,
or executables such as updates for common trusted applications. Hackers have become
very effective at making these files seem benign or obfuscating the malware to get past
traditional signature-based antivirus detection.
As a result of this new breed of file-based malware, sandboxing technology has become
an essential security layer at your network perimeter. Fortunately, cloud-based sandboxing
typically doesn’t require any additional hardware or software deployment – it simply
identifies suspect files at the gateway and sends them to a safe sandboxing infrastructure in
the cloud to detonate active content and monitor the behavior over time. It can be extremely
effective at blocking unknown threats like new ransomware attacks before they enter the

Best Practices for Firewall and Network Configuration

Unfortunately, many organizations operate with a flat network topology – with all their endpoints
connected into a common switch fabric. This topology compromises protection by enabling easy
lateral movement or propagation of network attacks within the Local Area Network since the firewall
has no visibility or control over the traffic through the switch.

A best practice is to segment the LAN into smaller subnets using zones or VLANs and then connecting
these together through the firewall to enable the application of anti-malware and IPS protection
between segments that can effectively identify and block threats attempting to move laterally on the

Whether you use zones or VLANs depends on your network segmentation strategy and scope, but
both offer similar security capabilities by providing the option to apply suitable security and control
over traffic movement between segments. Zones are ideal for smaller segmentation strategies
or networks with unmanaged switches. VLANs are the preferred method for segmenting internal
networks in most cases and offer the ultimate in flexibility and scalability, but require the use (and
configuration) of managed Layer 3 switches.

While it’s a best practice to segment your network, there’s no “best” way to segment a network.
You can segment your network by user type (internal, contractors, guests), by department (sales,
marketing, engineering), by service, device or role type (VoIP, Wi-Fi, IoT, computers, servers) or any
combination that makes sense for your network architecture. But generally, you will want to segment
less trusted and more vulnerable parts of your network from the rest, and also segment large networks
into smaller segments all with the aim of reducing the risk of threat penetration and propagation.

Sophos XG Firewall includes all the technology needed to help protect your organization from
the latest attacks like Wanna and Petya. In particular, XG Firewall includes one of the best
performing and most effective IPS engines on the market as recently confirmed by NSS
Labs. Our IPS patterns are updated frequently to detect the latest vulnerabilities and, in the
case of Wanna and Petya, had received pattern updates well before these outbreaks. And
since the initial attacks, additional patterns have been added to catch new variants.
XG Firewall also enables excellent protection against the spread of attacks on your network,
but as with any security product it must be given an opportunity to do its job.

Proper deployment and configuration is key to reducing the surface area of attack and minimizing
the risk and potential scope of propagation. XG Firewall offers flexible and easy segmentation
tools like zones and VLANs to secure your LAN and reduce the risk of lateral movement.
Firewall Best Practices to Block Ransomware Attacks like Wanna and Petya

And you don’t need to rip-and-replace anything to get all the great benefits of XG Firewall,
Intercept X, and Synchronized Security. You can deploy XG Firewall in-line with your existing
firewall, and Intercept X alongside your existing desktop antivirus client. Together they give
you unparalleled protection against ransomware and other advanced attacks. It’s next-gen
protection against next-gen threats.