Backdoor in xz

The upstream xz repository and the xz tarballs have been backdoored.

This backdoor is very indirect and only shows up when a few known specific criteria are met. Others may be yet discovered! However, this backdoor is at least triggerable by remote unprivileged systems connecting to public SSH ports.

This supply-chain attack targets .deb- and .rpm-based distributions, but the backdoored versions of xz or xz-utils (5.6.0 and 5.6.1) have made it only into rolling-release distributions such as Fedora Rawhide, Debian Testing/Sid, OpenSuse Tumbleweed, and Archlinux (where it is inactive).

The server of this blog is running Debian Testing and had the compromised version of xz-utils installed since March 17. The backdoor was reported last Friday, March 29. I've installed the patch provided by Debian on Saturday, March 30, and examined the system logs, which do not show any evidence that the system has been compromised in any way. In fact, according to my current understanding, the system did not meet all the requirements for the backdoor to be executed. However, I will remain vigilant and let the users of the server know if further action needs to be taken.

More links (in German): Heise 30.03.2024 09:35, Heise 30.03.2024 22:28, Heise 02.04.2024 17:10