When Older Windows Systems Won't Die

In a week when multiple vulnerabilities made headlines, a standout was CVE-2019-0708: a critical remote code execution (RCE) bug in Windows' Remote Desktop Services (RDS), formerly Terminal Services, affecting several in-support and out-of-support versions of Windows.

Microsoft reports that the RCE flaw, which has not yet been seen exploited in the wild, could be weaponized as a worm if exploited. The vulnerability is pre-authentication and requires no user interaction. Any future malware could propagate from vulnerable computer to vulnerable computer, similar to the way WannaCry spread to machines around the world in 2017.

How it works: once authenticated, attackers could connect to a target system via Remote Desktop Protocol (RDP) and send specially crafted requests. RDP is not vulnerable but it is part of the attack chain. If successful, the attacker could execute malicious code on the target system; install programs; view, edit, or delete data; or create new accounts with full user rights.

The fear of cybercriminals writing exploits for the bug prompted Microsoft to release security fixes and workarounds for older versions of Windows: Windows 2003 and XP in addition to still-supported Windows 7, Server 2008, and Server 2008 R2. In a blog post on the update, Simon Pope, director of the Microsoft Security Response Center (MSRC), called the out-of-band patch "unusual" and emphasized businesses to patch all affected systems as quickly as possible to prevent an attack.

But while a legacy patch may be rare for Microsoft, it's with good reason: many companies still run older versions of Windows due to the complications and challenges of system upgrades. And leaving those systems without a patch for the new, wormable RCE flaw would leave them exposed to possible such attacks.

After Microsoft disclosed the flaw, Alert Logic researchers scanned more than 4,000 customer sites to determine which were vulnerable. Of those, they found 61% of workloads run Windows 7 and Windows 2008, and 2.4% run Windows XP and 2003 – meaning nearly two-thirds of all businesses included are using older or unsupported versions of the operating system.

"One of the reasons that small and medium sized businesses were particularly affected is due to the fact that these organizations are more likely to run older systems, as their budgets and staffing constraints make it harder to upgrade," says Rohit Dhamankar, vice president of threat intelligence products at Alert Logic, adding that constant monitoring for them is "essential."

Kelly White, founder and CEO at RiskRecon, says it's "highly likely" cybercriminals are developing an exploit for this particular bug. Similar to the flaw exploited in the WannaCry campaign, CVE-2019-0708 has several traits to motivate attackers: exploitation yields remote system compromise, the service is commonly exposed online, it is remotely exploitable, and it doesn't require authentication to execute. A RiskRecon analysis of 10,000 companies showed 13% operate RDP on Internet-facing systems, putting them at higher risk for attack.

"Due to those factors, it's the perfect combination that motivates security researchers and exploit writers to write the exploit code for this, because a lot can be gained," he explains. "For the hackers, it's gold."

As we saw with WannaCry, thousands of legacy systems remain unpatched because they're running fragile software stacks nobody wants to touch, notes, Satya Gupta, cofounder and CTO at Virsec. But patching is always slower and more difficult than organizations want to admit because it's a disruptive process and can cause unintended problems. While businesses should act on Microsoft's alerts as soon as possible, there remain issues for "unpatchable" systems.

For Industrial Control Systems, Patching is Perilous

"Microsoft used a few key words in their advisory that should get everyone's attention: WannaCry, worm, pre-authentication, and remote code execution," says David Atch, vice president of security research at CyberX, a Boston-based IoT and ICS security company. In a recent analysis of traffic from more than 850 production OT networks, CyberX found 53% of websites were still running outdated versions of Windows, including Windows XP and 2000. Forty percent of industrial sites have at least one direct connection to the Internet.

Industrial firms will remember the damage caused by WannaCry, which "spread like wildfire" and disrupted production at Boeing, Honda, Nissan, Renault, FedEx, and Telefonica, he adds. CVE-2019-0708 gives attackers the ability to install backdoors, ransomware, and cryptomining malware on ICS/SCADA systems to disable safety controllers or shut down manufacturing lines. Many industrial companies rely on RDS to give remote operators and engineers access to control system environments. An attacker could target one machine to install code that could wreak havoc across the network.

"ICS environments are at greater risk of attackers exploiting this vulnerability due to such environments operating older Windows systems and systems that receive less frequent updates," explain Dragos intelligence analyst Selena Larson, and vulnerability analyst K. Reid Wightman, in a blog post on the bug. Engineering workstations, human machine interfaces, data historians, and OPC servers all run Windows, they point out.

Unlike most IT systems where "just patch" is frequent advice, Atch notes that patching ICS systems is a challenge because the process causes downtime and may being instabilities to production processes. "Upgrading to newer versions of Windows is also challenging because many of these systems are still running applications that were developed 10 or 15 years ago – especially in manufacturing environments – and upgrading them may cause applications to stop working, requiring access to developers that may no longer be available," he says.

Atch recommends a risk-based approach, and to prioritize patching for Internet-facing systems and corporate jumpbox systems that provide secure remote access from the IT network to the ICS network. He also advises network segmentation of the OT network, and isolating the OT network from IT network, to prevent the spread of malware in the event of an attack.

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