A stealth attack came close to compromising the world’s computers
I n 2020 XKCD, a popular online comic strip, published a cartoon depicting a teetering arrangement of blocks with the label: “all modern digital infrastructure”. Perched precariously at the bottom, holding everything up, was a lone, slender brick: “A project some random person in Nebraska has been thanklessly maintaining since 2003.” The illustration quickly became a cult classic among the technically minded, for it highlighted a harsh truth: the software at the heart of the internet is maintained not by giant corporations or sprawling bureaucracies but by a handful of earnest volunteers toiling in obscurity. A cyber-security scare in recent days shows how the result can be near-disaster.
On March 29th Andres Freund, an engineer at Microsoft, published a short detective story. In recent weeks he had noticed that SSH—a system to log on securely to another device over the internet—was running about 500 milliseconds more slowly than expected. Closer inspection revealed malicious code embedded deep inside XZ Utils, a piece of software designed for compressing data used inside the Linux operating system, which runs on virtually all publicly accessible internet servers. Those servers ultimately undergird the internet, including vital financial and government services. The malware would have served as a “master key”, allowing attackers to steal encrypted data or plant other malware.
The most interesting part of the story is how it got there. XZ Utils is open-source software, which means that its code is public and can be inspected or modified by anyone. In 2022 Lasse Collin, the developer who maintained it, found that his “unpaid hobby project” was becoming more onerous amid long-term mental-health issues. A developer going by the name Jia Tan, who had created an account the previous year, offered to help. For more than two years they contributed helpful code on hundreds of occasions, building up trust. In February they smuggled in the malware.
