The recent widespread attacks of WannaCry and NotPetya both used known vulnerabilities of legacy operating systems, namely SMB v1 protocol. In general, known vulnerabilities are easy to mitigate as long as patches and updates are provided. But in these cases, many organizations seem to have ignored the advice to patch their systems — or maybe not.

There are two main reasons for this negligence: Either organizations are not aware of the presence of legacy systems, or updating these systems isn’t as easy as it sounds.

In some environments, those legacy systems host applications that control vital business processes. Replacing or updating proprietary software is costly and sometimes virtually impossible, but that doesn’t mean you have to accept the risk of using legacy systems. The following security principles can help to minimize this risk at reasonable costs.

Identify Legacy Systems

Visibility and knowledge about the organization’s environment are crucial to an effective cyberdefense strategy. A discovery scan is a very efficient method to identify legacy systems. It also provides information about the network architecture and vulnerabilities on any system. Vulnerability scans should be done regularly from inside and outside the network.

Isolation and Strict Access Control

Systems that are no longer supported with patches should be quarantined from any other system environment, especially endpoint networks. A single legacy system can be the gateway for malware to spread throughout a network.

You must also ensure that those systems are not directly accessible from the internet, and guarantee that any communication with them is restricted to minimal need. This can be achieved by placing these systems in their own network segment behind a router or firewall.


Every system should be hardened according to its purpose. This is especially important for legacy systems. Hardening means to disable any unnecessary service and implement least privilege concepts to reduce the general exposure. Even legacy operating systems such as the outdated Windows versions 2000–2003 can be hardened through measures such as disabling the SMB protocol.


The purpose of security monitoring is to ensure that the system fulfills the defined security baseline and detects suspicious activities as early as possible. Since many attacks go hand in hand with starting or stopping processes or altering permissions, monitoring should include security configuration and authentication events. Security monitoring is especially vital for legacy systems.

These measures can help you reduce the risks that arise when updating a system is simply not an option. However, in most cases, vigilant updating and patch management are the keys to protecting your network from undead threats lurking within your legacy systems.

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