Posted on Monday, April 1, 2024.
Updated Wednesday, April 3, 2024.
Over a period of over two years, an attacker using the name “Jia Tan”worked as a diligent, effective contributor to the xz compression library,eventually being granted commit access and maintainership.Using that access, they installed a very subtle, carefully hidden backdoor into liblzma,a part of xz that also happens to be a dependency of OpenSSH sshdon Debian, Ubuntu, and Fedora, and other systemd-based Linux systems that patched sshd to link libsystemd.(Note that this does not include systems like Arch Linux, Gentoo, and NixOS, which do not patch sshd.)That backdoor watches for the attacker sending hidden commands at the start of an SSH session,giving the attacker the ability to run an arbitrary command on the target system without logging in:unauthenticated, targeted remote code execution.
The attack was
publicly disclosed on March 29, 2024 andappears to be the first serious known supply chain attack on widely used open source software.It marks a watershed moment in open source supply chain security, for better or worse.
