Explain Like I'm Five

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/

Chances are very, very high, that you are not nearly interesting enough to warrant someone utilizing said back door to discover your stash of furry lewds. The primary target for an exploit like this, is either nation state level (industrial/political espionage, tampering with financial markets, etc.) or criminal enterprise level going after high value targets. Trying to dragnet every random whoever to see if they have data worth compromising wouldn’t be much of a money maker.

That said, this is one of the dangers of using a rolling release. I was running endeavourOS and was likely exposed to the back door for a while. I’ve since switched back to Fedora, which was only exposed on its testing branch (rawhide).

TL;DR don't worry (for now) - it only impacts rpm and deb builds and impacted releases only really made it into OpenSuSe tumbleweed - if you're running bleeding edge maybe you need to worry a little.

A laymans explanation about what happens is that the malicious package uses an indirect linkage (via systemd) to openssh and overrides a crypto function which either:

• allows access to the system to a particular key
• allows remote code execution with a particular key

Or both!

I have secondhand info that privately the reverse engineering is more advanced, but nobody wants to lead with bad info.

As for what you should do? Unless you're running an rpm or deb based distro and you have version 5.6.0 or 5.6.1 of xz-utils installed, not much. If you are, well, that comes down to your threat model and paranoia level: either upgrade (downgrade) the package to a non-vulnerable version or dust off and nuke the site from orbit; it's the only way to be sure.

My system is too broken for this malware to work. I use Arch btw.

TL;DR: Simply downgrade to a version before 5.6.0, or follow the official recommendations for your distro. For Arch, for example, simply upgrade your system.

Explanation (from my understanding ): a malicious developer snuck a backdoor into xz, starting with version 5.6.0,and thankfully it was caught before it could do much damage. This seems to only affect Fedora and Debian based distros, or otherwise distros where ssh is patched to link to systemd, which in turn links to xz. Arch doesn't seem to be affected, but they took some preventative action. Again, follow the announcements from your distro, or just downgrade xz.

It is not yet clear what a malicious actor can do with that backdoor, but it seems, in affected systems, it enables remote code execution (if you don't know what that means, just know it's really bad), but last I checked security researchers were still analyzing the code. Things move fast, so maybe by now it is known.

Based on this very handy HN comment the long and short of it is that it would probably only have been a problem if you were running:

• A very recent version of liblzma5 - 5.6.0 or 5.6.1. This was added in the last month or so. If you're not on a rolling release distro, your version is probably older.

• A debian or RPM based distro of Linux on x86_64. In an apparent attempt to make reverse engineering harder, it does not seem to apply when built outside of deb or rpm packaging. It is also specific to Linux.

• Running OpenSSH sshd from systemd. OpenSSH as patched by some distros only pulls in libsystemd for logging functionality, which pulls in the compromised liblzma5.

So if all of those weren't true for you, you're most likely fine. Not a guarantee though since the backdoor's still being analyzed and that comment is a couple of days old, but as far as I can tell it's still reasonably accurate.

It would appear I explain things to five year olds very differently than people on Lemmy

Listening to Клетка while reading about this situation feels so cyber-esque.