TL;DR: Update immediately, especially if SSH is enabled. xz versions 5.6.0 & 5.6.1 are impacted. The article contains links to each distro’s specific instructions of what to do.
https://news.opensuse.org/2024/03/29/xz-backdoor/
Current research indicates that the backdoor is active in the SSH Daemon, allowing malicious actors to access systems where SSH is exposed to the internet.
In summary, the conditions for exploitation seem to be:
- xz version 5.6.0 or 5.6.1
- SSH with a patch that causes xz to be loaded
- SSH daemon enabled
Impact on distros
-
Arch Linux: Backdoor was present, but shouldn’t be able to activate. Updating is still strongly recommended.
-
Debian: Testing, Unstable, and Experimental are affected (update to
xz-utilsversion5.6.1+really5.4.5-1). Stable is not affected. -
Fedora: 41 is affected and should not be used. Fedora 40 may be affected (check the version of
xz). Fedora 39 is not affected. -
FreeBSD: Not affected.
-
Kali: Affected.
-
NixOS: NixOS unstable has the backdoor, but it should not be able to activate. NixOS stable is not affected.
-
OpenSUSE: Tumbleweed and MicroOS are affected. Update to
liblzma5version5.6.1.revertto5.4. Leap is not affected.
FYI: if you run freebsd you are not affected: https://lists.freebsd.org/archives/freebsd-security/2024-March/000248.html
Took me a while to find out so I thought I’d share.
Thanks, edited this into the post (along with the distros listed by LWN)
The story about this backdoor is really wild if it’s true https://lcamtuf.substack.com/p/technologist-vs-spy-the-xz-backdoor
That’s what all of the analysis is pointing to.
Since the analysis is not complete, the other thing people need to remember is that nobody knows if ssh was the only target or just the only one that was noticed. A ton of stuff uses lzma, including web browsers and password safes.
Why ssh? Does ssh use xz?
Ssh uses systemd and systemd uses lzma (xz)
Not directly, but it’s often integrated with systemd which does.
What may not be clear is the connection to SSH. And it’s a trip. Many Linux distros patch sshd to add systemd features, and libsystemd pulls the liblzma library. That means the liblzma initialization code gets run when sshd starts.
https://hackaday.com/2024/03/29/security-alert-potential-ssh-backdoor-via-liblzma/
Yes. ssh’s RSA encryption uses liblzm.
This analysis has some technical information on how it injects itself, conditionally, into deb and rpm from src tar.
Holy c… that’s quite a writeup, and what a rat’s nest of an exploit. A long time ago, I used to know some reverse engineering, then I got an
eval $zrKcTyto the got.plt.Wonder what it turns out to have been doing.
Im new to Linux does this include linux mint since it is based on Debian?
Likely not since most of these are dev or experimental of the latest version.
Check xz --version
If you’re not on the two listed above you’re fine.
As far as I can tell running xz directly should be fine, but for the extra paranoid check the version of the
xz-utilspackage. If it is safe, it will be either less than5.6.0, or it should be5.6.1+really5.4.5-1(xz5.4.5with a spoof version number to ensure compromised systems get the update).awesome thanks I did (xz --version) to check and it is using an unaffected version.
Void Linux is not affected too, they reversed to 5.4.X series the time this was published and it doesn’t use systemd neither patch openssh to use liblzma. https://github.com/void-linux/void-packages/discussions/49614
WSL2 2.1.5:
- (system) CBL-Mariner / Azure Linux: xz-libs 5.2.5-1.cm2
- Ubuntu 22.04.4 LTS: xz-utils 5.2.5-2ubuntu1
- Kali (rolling): Same fix as for Debian Testing (update to xz-utils version 5.6.1+really5.4.5-1)