In a nutshell, a backdoor was intentionally planted by a malicious actor in xz Utils, an open-source data compression utility widely used in Linux and other Unix-like operating systems. This discovery was made by Andres Freund, a developer and engineer working on Microsoft’s PostgreSQL offerings. He was troubleshooting performance problems on a Debian system. Specifically, SSH logins were consuming excessive CPU cycles and generating errors with Valgrind, a memory debugging tool. Through sheer luck and Freund’s careful eye, he eventually discovered that these issues were the result of updates made to xz Utils. Upon closer inspection, he found that updates to xz Utils were the result of a maliciously inserted backdoor. The backdoor, present in xz Utils versions 5.6.0 and 5.6.1, manipulated the sshd executable, allowing anyone with a predetermined encryption key to upload and execute arbitrary code on affected devices.