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From Trust to Threat: The XZ Utils Backdoor and Its Impact on OT Security

By Vince Kuchar, CEO of RMC & Brad Bekampis, Senior Cybersecurity Specialist

As the landscape of cybersecurity continues to change, it’s not uncommon to encounter threats that redefine our understanding of vulnerability and resilience.

The recent discovery of a covert and sophisticated backdoor in ‘XZ Utils’ – a set of libraries crucial to Linux operating systems – serves as a stark reminder of this constant battle.

Initially detected by PostgreSQL maintainer Andres Freund, the backdoor exposed a significant vulnerability affecting a wide range of Linux distributions. This discovery triggered urgent responses from the cybersecurity community, including security advisories from the Cybersecurity and Infrastructure Security Agency (CISA), underscoring the pervasive risks inherent to software supply chains.

The breach demonstrates a fundamental vulnerability in the trust mechanisms underpinning software development, especially in open-source projects. In this scenario, the attacker built trust and credibility over approximately three years, all while routinely updating core software components and libraries. After establishing trust over a long period of legitimate activities, the attacker inserted a backdoor into a routine update of XZ Utils, jeopardizing millions of systems via an exposed Secure Shell (SSH) service – a maneuver reflective of a sophisticated cyber operator with advanced capabilities and significant resources. Such elaborate and sustained efforts to infiltrate widespread internet infrastructure are often characteristic of well-resourced organizations or nation-state actors.

It illuminates a tension at the heart of software security: the balance between openness and trust. While open-source software offers transparency, allowing anyone to scrutinize and detect flaws, it also opens the door for sophisticated attackers to subtly introduce vulnerabilities. The discovery of the backdoor by a Microsoft engineer, prompted by a slight delay during a routine login, underscores the element of chance in such detections. This discovery highlights the necessity of vigilant and continuous monitoring of software systems, reminding us that what might seem like minor anomalies could potentially be indicators of significant threats.

When Patching Backfires: The Hidden Risks of Software Updates

Furthermore, this situation compels us to examine the trust we place in software updates. Just as we rarely question the integrity of a Windows update, users of open-source software generally assume updates are safe and authentic. This breach challenges that assumption and has sparked a debate on the security of open- versus closed-source models. Could an insider at a major company like Microsoft also turn rogue?

Global supply chain attacks are increasingly prevalent because they offer attackers a less guarded route to a wide array of targets. We can apply the fundamentals of this case to OT security, considering the potential consequences if the software that runs our critical infrastructure were compromised in a similar manner.

One might compare it to routinely updating a device without a second thought about security. We trust these updates implicitly, but this incident lays bare the merits of a zero-trust approach, where every modification is scrutinized. Implementing such stringent checks, however, presents its own challenges. Delaying updates might mitigate some risks while leaving systems temporarily vulnerable to other risks – a classic security dilemma.

This highlights the necessity of taking a nuanced approach to patch management. Regular patch management, a cornerstone of OT Vulnerability Management, is typically advocated by cybersecurity experts to safeguard systems against known threats. As we emphasized in our previous RMC blog on OT Vulnerability Management, coordinated patching schedules with vendors are crucial to ensure the security of systems.

However, the XZ Utils case presents an interesting dilemma. While the intent behind regular updates is to secure systems, this incident illustrates how even these protective measures can inadvertently introduce vulnerabilities, particularly through sophisticated supply chain attacks. The breach involved a backdoor embedded in a library used by Linux operating systems, including those in many OT environments as well as systems used by ethical hackers for penetration testing, such as Kali Linux. This not only raises a significant concern about the direct impact on operational technologies but also highlights a potential secondary risk: ethical hackers, relying on these systems for security assessments, might have inadvertently been affected by this update. If they updated their versions of Kali during this time, there’s a real possibility they could have exposed their clients to unnecessary risks.

This deepens the complexity of the issue: what if a similar attack were executed on platforms like OPC Unified Architecture (OPC-UA), widely used in OT environments to allow products from different vendors to communicate with each other? The implications could be far-reaching, affecting not just operational systems but also the very tools used to protect them.

The potential impacts of such an attack could be profound. For example, a vulnerability found in the core components of a protocol like OPC-UA could affect several products and vendors, which could be used to conduct wide-spread attacks against both OPC servers and clients. This scenario was demonstrated and presented at Defcon 31. Claroty researchers (Team 82) presented findings after months of research uncovering dozens of CVEs including denial of service, remote code execution, and more against big-name vendors using OPC-UA. Additionally, they created an open-source exploit framework from the tools developed during their research of OPC-UA. While these vulnerabilities were uncovered by ethical researchers, it raises an important question: how many vulnerabilities in open-source software are identified by unethical groups, who do not publicize their findings, and may seek to negatively impact critical infrastructure.

Rethinking Patch Management: Security Benefits vs. Potential Threats

While it is essential to address known vulnerabilities in any environment, the introduction of new code through patches can also open doors to hidden threats. The inherent risks and benefits of patch management form a double-edged sword, particularly in the open-source domain where transparency can both aid security efforts and expose systems to targeted attacks.

Reflecting on the XZ Utils incident, it’s evident that while patch management is an integral activity within vulnerability management, it is not foolproof. The sophisticated nature of the attack – carried out over years to gain enough trust to introduce a backdoor – highlights an advanced threat landscape where attackers can exploit some of the very mechanisms designed to protect the supply chain.

While the benefits of patching outweigh the risks, this incident serves as a reminder of the low-probability yet high-impact risks of sophisticated supply chain cyberattacks. It emphasizes the need for a more nuanced approach to patch management, particularly in delicate OT environments, where the cost of a breach could extend far beyond data loss and could result in actual physical damage and operational downtime.

The attack on XZ Utils is a unique cybersecurity event given it was an orchestrated and patiently crafted assault on the trust and reliability of open-source ecosystems. The attackers did not rush; they spent years building credibility and integrating themselves within the community to carry out what is arguably one of the most strategically executed supply chain attacks in history. Their methodical approach underscores a dangerous mix of competence and malice, raising important questions about the safety of similar components in OT environments that govern everything from water utilities to power grids.

Enabling Operations with Proactive Security Measures

At RMC, we understand that effective cybersecurity in critical infrastructure isn’t just about reacting to threats – it’s about proactively managing and anticipating them. This is especially critical in the context of patch management, where the right strategies can prevent vulnerabilities from being exploited and mitigate the complexities introduced by necessary updates. Our approach emphasizes not only identifying vulnerabilities but also understanding the broader implications of how patches affect OT environments.

Our expertise in OT cybersecurity, combined with a deep knowledge in penetration testing, positions RMC to provide strategic guidance that transcends traditional security measures. We help organizations navigate the intricate balance between maintaining up-to-date systems and ensuring that these updates prevent the introduction of new vulnerabilities. By comprehensively detailing and understanding these dynamics, we empower our clients to protect their critical operations against both conventional and sophisticated cyber threats.

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