• fireshell@lemmy.worldEnglish
    0·
    1 year ago

    Since the actual operation of the liblzma SSH backdoor payload is still unknown, there’s a protocol for securing your impacted systems:

    • Consider all data, including key material and secrets on the impacted system as compromised. Expand the impact to other systems, as needed (for example: if a local SSH key is used to access a remote system then the remote system must be considered impacted as well, within the scope the key provides).

    • Wipe the impacted host and reinstall it from scratch. Use known good install that does not contain the malicious payload. Generate new keys and passwords. Do not reuse any from the impacted systems.

    • Restore configuration and data from backups, but from before the time the malicious liblzma package was installed. However, be careful not to allow potentially leaked credentials or keys to have access to the newly installed system (for example via $HOME/.ssh/authorized_keys).

    This handles the systems themselves. Unfortunately any passwords and other credentials stored, accessed or processed with the impacted systems must be considered compromised as well. Change passwords on web sites and other services as needed. Consider the fact that the attacker may have accessed the services and added ways to restore access via for example email address or phone number in their control. Check all information stored on the services for correctness.

    This is a lot of work, certainly much more than just upgrading the liblzma package. This is the price you have to pay to stay safe. Just upgrading your liblzma package and hoping for the best is always an option, too. It’s up to you to decide if this is a risk worth taking.

    This recovery protocol might change somewhat once the actual operation of the payload is figured out. There might be situations where the impact could be more limited.

    As an example: If it turns out that the payload is fully contained and only allows unauthorized remote access via the tampered sshd, and the host is not directly accessible from the internet (the SSH port is not open to internet) this would mean that it might be possible to clean up the system locally without full reinstall.

    However, do note that the information stored on the system might have still been leaked to outside world. For example leaked ssh keys without a passphrase could still afford the attacker access to remote systems.

    This is a long con, and honestly the only people at fault are the bad actors themselves. Assuming Jia Tan’s GitHub identity and pgp key weren’t compromised by someone else, this backdoor appears to be the culmination of three years of work.

      • OsrsNeedsF2P@lemmy.ml
        0·
        1 year ago

        The backdoor wasn’t in the source code, only in the distributed binary. So reproducible builds would have flagged the tar as not coming from what was in Git

        • Virulent@reddthat.com
          0·
          1 year ago

          Not exactly - it was in the source tarbal available for download from the releases page but not the git source tree.

        • chameleon@kbin.social
          0·
          1 year ago

          Reproducible builds generally work from the published source tarballs, as those tend to be easier to mirror and archive than a Git repository is. The GPG-signed source tarball includes all of the code to build the exploit.

          The Git repository does not include the code to build the backdoor (though it does include the actual backdoor itself, the binary “test file”, it’s simply disused).

          Verifying that the tarball and Git repository match would be neat, but is not a focus of any existing reproducible build project that I know of. It probably should be, but quite a number of projects have legitimate differences in their tarballs, often pre-compiling things like autotools-based configure scripts and man pages so that you can have a relaxed ./configure && make && make install build without having to hunt down all of the necessary generators.

          • flying_sheep@lemmy.ml
            0·
            1 year ago

            Time to change that tarball thing. Git repos come with built in checksums, that should be the way to go.

            • tal@lemmy.todayEnglish
              0·
              1 year ago

              Honestly, while the way they deployed the exploit helped hide it, I’m not sure that they couldn’t have figured out some similar way to hide it in autoconf stuff and commit it.

              Remember that the attacker had commit privileges to the repository, was a co-maintainer, and the primary maintainer was apparently away on a month-long vacation. How many parties other than the maintainer are going to go review a lot of complicated autoconf stuff?

              I’m not saying that your point’s invalid. Making sure that what comes out of the git repository is what goes to upstream is probably a good security practice. But I’m not sure that it really avoids this.

              Probably a lot of good lessons that could be learned.

              • It sounds like social engineering, including maybe use of sockpuppets, was used to target the maintainer, to get him to cede maintainer status.

              • Social engineering was used to pressure package maintainers to commit.

              • Apparently automated software testing software did trip on the changes, like some fuzz-tesing software at Google, but the attacker managed to get changes committed to avoid it. This was one point where a light really did get aimed at the changes. That being said, the attacker here was also a maintainer, and I don’t think that the fuzzer guys consider themselves responsible for identifying security holes. And while it did highlight the use of ifunc, it sounds like it was legitimately a bug. But, still, it might be possible to have some kind of security examination taking place when fuzzing software trips, especially if the fuzzing software isn’t under control of a project’s maintainer (as it was not, here).

              • The changes were apparently aimed at getting in shortly before Ubuntu freeze; the attacker was apparently recorded asking and ensuring that Ubuntu fed off Debian testing. Maybe there needs to be more-attention paid to things that go in shortly before freeze.

              • Part of the attack was hidden in autoconf scripts. Autoconf, especially with generated data going out the door, is hard to audit.

              • As you point out, using a chain that ensures that a backdoor that goes into downstream also goes into git would be a good idea.

              • Distros should probably be more careful about linking stuff to security-critical binaries like sshd. Apparently this was very much not necessary to achieve what they wanted to do in this case; it was possible to have a very small amount of code that performed the functionality that was actually needed.

              • Unless the systemd-notifier changes themselves were done by an attacker, it’s a good bet that the Jia Tan group and similar are monitoring software, looking for dependencies like the systemd-notifier introduction. Looking for similar problems that might affect similar remotely-accessible servers might be a good idea.

              • It might be a good idea to have servers run their auth component in an isolated module. I’d guess that it’d be possible to have a portion of sshd that accepts incoming connections (and is exposed to the outside, unauthenticated world) as an isolated process. That’d be kind of inetd-like functionality. The portion that performed authentication (and is also running exposed to the outside) as an isolated process, and the code that runs only after authentication succeeds run separately, with only the latter bringing in most libraries.

              • I’ve seen some arguments that systemd itself is large and complicated enough that it lends itself to attacks like this. I think that maybe there’s an argument that some sort of distinction should be made between more- or less-security-critical software, and different policies applied. Systemd alone is a pretty important piece of software to be able to compromise. Maybe there are ways to rearchitect things to be somewhat more-resilient and auditable.

              • I’m not familiar with the ifunc mechanism, but it sounds like attackers consider it to be a useful route to hide injected code. Maybe have some kind of auditing system to look for that.

              • The attacker modified the “in the event of an identified security hole” directions to discourage disclosure to anyone except the project for a 90-day embargo period, and made himself the contact point. That would have provided time to continue to use the exploit. In practice, perhaps software projects should not be the only contact point – perhaps it should be the norm to both notify software projects and a separate, unrelated-to-a-project security point. That increases the risk of the exploit leaking, but protects against compromise of the project maintainership.

    • Daniel Quinn@lemmy.caEnglish
      0·
      1 year ago

      Why didn’t this become a thing? Surely in 2024, we should be able to build packages from source and sign releases with a private key.

      • Natanael@slrpnk.net
        0·
        1 year ago

        It’s becoming more of a thing but a lot of projects are so old that they haven’t been able to fix their entire build process yet

    • 30p87@feddit.de
      0·
      1 year ago

      I upgraded to 5.6.0-1 on the 28th Februar already. Over a month ago. On a server. That’s the first time Arch testing has fucked me so hard lol.

      • tal@lemmy.todayEnglish
        0·
        1 year ago

        You probably are fairly safe. Yeah, okay, from a purely-technical standpoint, your server was wide-open to the Internet. But unless some third party managed to identify and leverage the backdoor in the window between you deploying it and it being fixed, only the (probably state-backed) group who are doing this would have been able to make use of it. They probably aren’t going to risk exposing their backdoor by exploiting it on your system unless they believe that you have something that would be really valuable to them.

        Maybe if you’re a critical open-source developer, grabbing your signing keys or other credentials might be useful, given that they seem to be focused on supply-chain attacks, but for most people, they probably just aren’t worth the risk. Only takes them hitting some system with an intrusion-detection system that picks up on the breakin, them leaving behind traces, and some determined person tracking down what happened, and they’ve destroyed their exploit.

  • chameleon@kbin.social
    0·
    1 year ago

    This is a fun one we’re gonna be hearing about for a while…

    It’s fortunate it was discovered before any major releases of non-rolling-release distros were cut, but damn.

    • rolaulten@startrek.website
      0·
      1 year ago

      That’s the scary thing. It looks like this narrowly missed getting into Debian and RH. Downstream downstream that is… everything.

    • tal@lemmy.todayEnglish
      0·
      1 year ago

      Apparently the backdoor reverts back to regular operation if the payload is malformed or the signature from the attacker’s key doesn’t verify. Unfortunately, this means that unless a bug is found, we can’t write a reliable/reusable over-the-network scanner.

      Maybe not. But it does mean that you can write a crawler that slams the door shut for the attacker on any vulnerable systems.

      EDIT: Oh, maybe he just means that it reverts for that single invocation.

  • Wes_Dev@lemmy.ml
    0·
    1 year ago

    Damn fine work all around.

    I know this is an issue fraught with potential legal and political BS, and it’s impossible to check everything without automation these days, but is there an organization that trains and pays people to work as security researchers or QA for open source projects?

    Basically, a watchdog group that finds exploitable security vulnerabilities, and works with individuals or vendors to patch them? Maybe make it a publicly owned and operated group with mandatory reporting of some kind. An international project funded by multiple governments, where it’s harder for a single point of influence to hide exploits, abuse secrets, or interfere with the researchers? They don’t own or control any code, just find security issues and advise.

    I don’t know.

    Just thinking that modern security is getting pretty complicated, with so many moving parts and all.

  • gwendolencopper@kbin.social
    0·
    1 year ago

    could a Flatpak contain one of the backdoored builds of xz or liblzma? Is there a way to check? Would such a thing be exploitable, or does this backdoor only affect ssh servers?

    • chameleon@kbin.social
      0·
      1 year ago

      The base runtime pretty much every Flatpak uses includes xz/liblzma, but none of the affected versions are included. You can poke around in a base runtime shell with flatpak run --command=sh org.freedesktop.Platform//23.08 or similar, and check your installed runtimes with flatpak list --runtime.

      23.08 is the current latest version used by most apps on Flathub and includes xz 5.4.6. 22.08 is an older version you might also still have installed and includes xz 5.2.12. They’re both pre-backdoor.

      It seems there’s an issue open on the freedesktop-sdk repo to revert xz to an even earlier version predating the backdoorer’s significant involvement in xz, which some other distros are also doing out of an abundance of caution.

      So, as far as we know: nothing uses the backdoored version, even if it did use that version it wouldn’t be compiled in (since org.freedesktop.Platform isn’t built using Deb or RPM packaging and that’s one of the conditions), even if it was compiled in it would to our current knowledge only affect sshd, the runtime doesn’t include an sshd at all, and they’re still being extra cautious anyway.

      One caveat: There is an unstable version of the runtime that does have the backdoored version, but that’s not used anywhere (I don’t believe it’s allowed on Flathub since it entirely defeats the point of it).

  • capt_kafei@lemmy.caEnglish
    0·
    1 year ago

    Damn, it is actually scary that they managed to pull this off. The backdoor came from the second-largest contributor to xz too, not some random drive-by.

    • Alex@lemmy.ml
      0·
      1 year ago

      Time to audit all there contributions although it looks like they mostly contribute to xz. I guess we’ll have to wait for comments from the rest of the team or if the whole org needs to be considered comprimised.

        • cjk@feddit.de
          0·
          1 year ago

          Either that or the attacker was very good at choosing their puppet…

          • Alex@lemmy.ml
            0·
            1 year ago

            Well the account is focused on one particular project which makes sense if you expect to get burned at some point and don’t want all your other exploits to be detected. It looks like there was a second sock puppet account involved in the original attack vector support code.

            We should certainly audit other projects for similar changes from other psudoanonymous accounts.

  • fireshell@lemmy.worldEnglish
    0·
    1 year ago

    Some no-name came and without any problems asked to become a maintainer in a project used in almost any distro, took it over, put a backdoor in there and no one had any questions? In this case, everything turned out thanks to pure chance. Noname screwed up his backdoor, which attracted the attention of a guy from Microsoft, and out of boredom, he dug up what was what. And if I hadn’t messed up, or that guy from Microsoft decided to go drink beer instead of poking around in the xz code, then no one would have discovered anything. It’s scary to imagine how many of these nonames are sitting in all these thousands of open source projects, waiting in the wings to roll out a malicious patch.