this post was submitted on 31 Mar 2024
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Explain Like I'm Five

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ELI5: The Linux xz backdoor situation (pawb.social)
submitted 7 months ago by VinesNFluff@pawb.social to c/explainlikeimfive@lemmy.world
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PLEASE. I keep seeing it in memes. As I understand it the latest version of the xz package (present in rolling release distros like Arch and SUSE Tumbleweed) has "a backdoor", but I have no earthly clue what can be done by malicious folks with access to that backdoor or if I should be afraid or how to check if my distro is compromised or how to prevent damage if it is or (...)

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[–] ashaman2007@lemm.ee 30 points 7 months ago (9 children)

Fairly simple explanation by arstechnica: “The malicious versions [of xz], researchers said, intentionally interfere with authentication performed by SSH, a commonly used protocol for connecting remotely to systems. SSH provides robust encryption to ensure that only authorized parties connect to a remote system. The backdoor is designed to allow a malicious actor to break the authentication and, from there, gain unauthorized access to the entire system. The backdoor works by injecting code during a key phase of the login process.”

Also from the article, you should check if your distro is offering a downgrade from the affected 5.6.x packages. Right now the exploit is not fully understood. For example, openSUSE recommends a full reinstall of Tumbleweed if an SSH server was enabled, just to mitigate risk.

https://arstechnica.com/security/2024/03/backdoor-found-in-widely-used-linux-utility-breaks-encrypted-ssh-connections/

https://news.opensuse.org/2024/03/29/xz-backdoor/

[–] VinesNFluff@pawb.social 9 points 7 months ago* (last edited 7 months ago) (6 children)

I was on EndeavourOS (Arch-derived), but switched to SUSE Tumbleweed like, this weekend.

But hold up

So if the backdoor is all about exploiting ssh to gain full system access, and ssh was never enabled in my OS I'm in the clear regardless?

[–] ashaman2007@lemm.ee 8 points 7 months ago (2 children)

Just to be sure, you should check whether SSHD is enabled: sudo systemctl status sshd.service If you never enabled it and it's disabled+inactive, then no need to reinstall Tumbleweed per the current guidance. Also you can double check your version of xz to make sure it's downgraded, the downgraded version for Tumbleweed should look like this:

sudo zypper search -vi xz
Loading repository data...
Reading installed packages...

S  | Name | Type    | Version               | Arch   | Repository
---+------+---------+-----------------------+--------+------------------
i+ | xz   | package | 5.6.1.revertto5.4-3.2 | x86_64 | update-tumbleweed
    name: xz
[–] VinesNFluff@pawb.social 4 points 7 months ago* (last edited 7 months ago)

Checked. We good. Thanks, stranger.

[–] qaz@lemmy.world 1 points 7 months ago

What if it was enabled but it was disabled in the firewall so it could only be used from the device itself?

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