[arch-announce] The xz package has been backdoored

From: "Arch Linux: Recent news updates: David Runge" arch-announce@lists.archlinux.org

TL;DR: Upgrade your systems and container images now!

As many of you may have already read 1, the upstream release tarballs for xz in version 5.6.0 and 5.6.1 contain malicious code which adds a backdoor.

This vulnerability is tracked in the Arch Linux security tracker 2.

The xz packages prior to version 5.6.1-2 (specifically 5.6.0-1 and 5.6.1-1) contain this backdoor.

We strongly advise against using affected release artifacts and instead downloading what is currently available as latest version!

Upgrading the system

It is strongly advised to do a full system upgrade right away if your system currently has xz version 5.6.0-1 or 5.6.1-1 installed:

pacman -Syu

Regarding sshd authentication bypass/code execution

From the upstream report 1:

> openssh does not directly use liblzma. However debian and several other distributions patch openssh to support systemd notification, and libsystemd does depend on lzma.

Arch does not directly link openssh to liblzma, and thus this attack vector is not possible. You can confirm this by issuing the following command:

ldd "$(command -v sshd)"

However, out of an abundance of caution, we advise users to remove the malicious code from their system by upgrading either way. This is because other yet-to-be discovered methods to exploit the backdoor could exist.

URL: https://archlinux.org/news/the-xz-package-has-been-backdoored/