The problem, he found, was in the liblzma data compression library, which is part of the XZ package, and he concluded that “The upstream xz repository and the xz tarballs have been backdoored.”
Which Linux distributions have been affected by the backdoored XZ packages?
Red Hat has confirmed that Fedora Rawhide and Fedora Linux 40 beta contained affected versions of the xz libraries, and that no versions of Red Hat Enterprise Linux are affected.
XZ Utils was authored by and is still led by Lasse Collin, but the backdoor was introduced by someone that went by “Jia Tan”, who became – over several years, with the help of sock puppet accounts and trust-building via social engineering – a prolific maintainer of the software, and did other things to keep the existence of the backdoor under wraps.
“The backdoor attempt was a very serious one, with a very high bar of knowledge, research, development and tradecraft to reach this far into the Linux ecosystem. Additionally, changes made by the threat actor on Github span multiple years, and include things like introducing functions incompatible with OSS Fuzzer due to outstanding small issues since 2015, then getting OSS Fuzzer to exclude XZ Utils from scanning last year,” researcher Kevin Beaumont noted.
“The backdoor itself is super well put together, and even includes the ability to remotely deactivate and remove the backdoor via a kill command. Several days in, despite global focus, I haven’t seen anybody who has finished reverse engineering it.”
