The story of the XZ backdoor is not simply about a clever attacker or an observant engineer. It is about the structural reality of the modern internet, a global digital economy built on layers of software that resemble a Jenga tower, where each block looks small in isolation but removing the wrong one sends the whole structure wobbling.
At the centre of this incident was XZ Utils, a compression library that most people have never heard of and never will. It has no venture funding, no marketing team, no public profile worth speaking of. It simply and quietly compresses data inside Linux systems across the planet, and for years it was maintained largely as a side project by someone doing it in their spare time. That arrangement is not unusual. It is, in fact, entirely normal.
1. The Printer, the Philosophy, and the Scale Explosion
Linux grew out of a philosophical objection to closed systems. When Richard Stallman was unable to modify proprietary printer software to fix a jam notification issue at MIT in the nineteen eighties, his frustration triggered the Free Software movement, the GNU project built the tooling that followed, and Linus Torvalds eventually wrote the kernel that brought it all together into a system anyone could inspect, modify, and redistribute.
That openness enabled extraordinary growth, to the point where Linux now runs cloud infrastructure, financial systems, telecommunications networks, mobile devices, and most of the modern web, and it is genuinely difficult to find a sector that does not depend on it in some form. But that same openness also enabled scale without proportional funding, and the gap between those two things is where the danger lives.
Many foundational open source projects are maintained by individuals or very small teams who work evenings and weekends, some of whom receive sponsorship and many of whom do not, while the world runs on their code and their day job might be something entirely unrelated. XZ was one of those projects: important but not famous, critical but not celebrated, infrastructure in the purest sense, invisible until it fails.
2. The Jenga Tower Nobody Admits Exists
The internet is like a Jenga tower in which each block represents a library, a tool, a protocol, a dependency, and on top of those blocks sit applications, and on top of applications sit services, and on top of services sit entire economies. Here is what that looks like in simplified form:
+----------------------+
| Banking Platforms |
+----------------------+
| Cloud Services |
+----------------------+
| Web Servers |
+----------------------+
| SSH OpenSSL |
+----------------------+
| glibc XZ Utils |
+----------------------+
| Linux Kernel |
+----------------------+
| Hardware |
+----------------------+Each layer assumes the stability of the one beneath it, and the higher you build, the less you tend to think about the blocks at the bottom. The danger is not only that a block can be malicious, but that a block can be fragile because it is maintained by someone exhausted, under-resourced, or overwhelmed, and as the tower grows taller, the importance of those smallest blocks only increases. What began as a modest compression utility becomes a critical dependency for authentication pathways in operating systems deployed globally, and a tiny project becomes systemic not through any deliberate design decision but as an emergent property of reuse.
3. When Side Hustles Become Critical Infrastructure
The uncomfortable truth is that much of the modern internet rests on projects that began as side hustles, where a developer scratched an itch, the tool gained adoption, it became a dependency, other tools depended on it, and soon thousands of organisations found themselves relying on something that was never designed with global criticality in mind.
XZ was reportedly struggling to keep up with maintenance, and burnout is common in small open source projects where issue queues grow, release management becomes stressful, and contributors come and go with little warning. When someone new arrives offering help in that environment, their assistance is usually welcomed without much suspicion, which is precisely what happened here, as a contributor gradually gained trust and influence before eventually acquiring the ability to introduce a malicious change. The attack was patient rather than loud, exploiting social dynamics as much as technical pathways, and the Jenga analogy sharpens considerably in this light: if one block at the bottom is tired, distracted, or under pressure, the integrity of the entire tower becomes contingent on their resilience.
4. The Anatomy of Stacked Dependence
Modern systems are compositional in ways that most of the people who depend on them never consider. A bank does not write its own operating system; it deploys Linux, which depends on libraries, which depend on other libraries, with package managers resolving thousands of dependencies automatically and largely invisibly. A simplified dependency cascade looks like this:
Financial Application
|
+-- Web Framework
|
+-- System Libraries
|
+-- Compression Library
|
+-- Maintained by Two HumansThe top of this chain might generate billions in revenue while the bottom is maintained by volunteers with limited time, and that disproportion is not a criticism of open source so much as a reality of scale. Reuse is efficient, it avoids duplication, it accelerates innovation, but it also concentrates risk in ways that are easy to ignore when everything is working, which is most of the time, which is precisely what makes the risk so easy to ignore.
The XZ backdoor was discovered because a developer noticed that SSH logins were slightly slower than expected, and that anomaly triggered deeper analysis that exposed the malicious code before it propagated widely into stable enterprise releases. The tower shook, but it did not fall.
5. Transparency Is Necessary but Not Sufficient
The original Linux philosophy assumed that openness would lead to rapid detection of problems, and in many cases it does, but openness does not guarantee attention, and code can be entirely public and still effectively unreviewed if no one has the bandwidth to inspect it carefully. When projects graduate from hobbyist tools to critical infrastructure, the maintenance model must evolve with them, because it cannot continue to rely purely on goodwill and spare time when the economic value extracted from these projects so dramatically exceeds the funding reinvested into them.
The Jenga tower metaphor reveals another uncomfortable truth here: the higher the tower grows, the more stable it appears to the people building on top of it, and the easier it becomes to assume that because it has not fallen, it is safe. In reality the structural tension increases with height, and the XZ incident should not be framed as an isolated near miss but as a signal that foundational layers require sustained investment, governance, and scrutiny that is proportional to their actual impact on the systems that depend on them.
6. The Structural Lesson
Linux began with a protest against closed control, flourished because distributed collaboration outperformed central planning, and now underpins global infrastructure in ways that its original architects could not have anticipated. The internet is not a single system but a stack of interdependent components assembled over decades, in which small projects become massive through reuse, side hustles become systemic dependencies, and invisible libraries become authentication gateways for the global economy.
The Jenga tower still stands, which is reassuring, and also a reminder that the smallest blocks at the bottom are precisely the ones that deserve the most attention.