syslog-ng VS systemd

Syslog-ng can feed splunk directly via HEC without having to use heavy forwarders. Earlier you had to hand configure it via the http () destination, v4.2 added this via a separate destination driver. https://github.com/syslog-ng/syslog-ng/releases/tag/syslog-ng-4.2.0

What we do internally is use [syslog-ng](https://github.com/syslog-ng/syslog-ng) to read the journald socket and push to a remote and into Kafka. I think journald works well as a structured logging tool, but it's certainly deficient in other ways

[12] https://github.com/syslog-ng/syslog-ng/releases/tag/syslog-ng-3.31.1

https://github.com/systemd/systemd/issues/32028#issuecomment...

There are some very compelling arguments made there if you care to read them

The PR for changing compression libraries to use dlopen() was opened several weeks before the xz-utils backdoor was revealed.

https://github.com/systemd/systemd/pull/31550

I find this the most plausible explanation by far:

* The highly professional outfit simply did not see teknoraver's commit to remove liblzma as standard dependency of systemd build scripts coming.

* The race was on between their compromised code and that commit. They had to win it, with as large a window as possible.

* This caused serious errors.

* The performance regression is __not__ big. It's lucky Andres caught it at all. It's also not necessarily all that simple to remove it. It's not simply a bug in a loop or some such.

* The payload of the 'hack' contains fairly easy ways for the xz hackers to update the payload. They actually used it to remove a real issue where their hackery causes issues with valgrind that might lead to discovering it, and they also used it to release 5.6.1 which rewrites significant chunks; I've as yet not read, nor know of any analysis, as to why they changed so much.

Extra info for those who don't know:

https://github.com/systemd/systemd/commit/3fc72d54132151c131...

That's a commit that changes how liblzma is a dependency of systemd. Not because the author of this commit knew anything was wrong with it. But, pretty much entirely by accident (although removing deps was part of the point of that commit), almost entirely eliminates the value of all those 2 years of hard work.

And that was with the finish line in sight for the xz hackers: On 24 feb 2024, the xz hackers release liblzma 5.6.0 which is the first fully operational compromised version. __12 days later systemd merges a commit that means it won't work__.

So now the race is on. Can they get 5.6.0 integrated into stable releases of major OSes _before_ teknoraver's commit that removes liblzma's status as direct dep of systemd?

I find it plausible that they knew about teknoraver's commit _just before_ Feb 24th 2024 (when liblzma v5.6.0 was released, the first backdoored release), and rushed to release ASAP, before doing the testing you describe. Buoyed by their efforts to add ways to update the payload which they indeed used - March 8th (after teknoraver's commit was accepted) it was used to fix the valgrind issue.

So, no, I don't find this weird, and I don't think the amateurish aspects should be taken as some sort of indication that parts of the outfit were amateuristic. As long as it's plausible that the amateuristic aspects were simply due to time pressure, it sounds like a really bad idea to make assumptions in this regard.

On 2024-02-29, a PR was sent to stop linking liblzma into libsystemd [0].

Kevin Beaumont speculated [1] that "Jia Tan" saw this and immediately realized it would have neutered the backdoor and thus began to rush to avoid losing the very significant amount of work that went into this exploit; I think he's right. That rush caused the crashing seen in 5.6.0 and the lack of polish which could have eliminated or reduced the performance regressions which were the entire reason this was caught in the first place; they simply didn't have the time because the window had started to close and they didn't want all their work to be for nothing.

[0]: https://github.com/systemd/systemd/pull/31550

[1]: https://doublepulsar.com/inside-the-failed-attempt-to-backdo...

sshd is started by systemd.

systemd has several ways of starting programs and waiting until they're "ready" before starting other programs that depend on them: Type=oneshot, simple, exec, forking, dbus, notify, ...

A while back, several distro maintainers found problems with using Type=exec (?) and chose Type=notify instead. When sshd is ready, it notifies systemd. How you do notification is you send a datagram to systemd's unix domain socket. That's about 10 lines of C code. But to make life even simpler, systemd also provides the one-line sd_notify() call, which is in libsystemd.so. This library is so other programmers can easily integrate with systemd.

So the distro maintainers patched sshd to use the sd_notify() function from libsystemd.so

What else is in libsystemd.so? That's right, systemd also does logging. All the logging functions are in there, so user programs can do logging the systemd way. You can even _read_ logs, using the functions in libsystemd.so. For example, sd_journal_open_files().

By the way... systemd supports the environment variable SYSTEMD_JOURNAL_COMPRESS which can be LZ4, XZ or ZSTD, to allow systemd log files to be compressed.

So, if you're a client program, that needs to read systemd logs, you'll call sd_journal_open_files() in libsystemd.so, which may then need liblz4, liblzma or libzstd functions.

These compression libraries could be dynamically loaded, should sd_journal_open_files() need them - which is what https://github.com/systemd/systemd/pull/31550 submitted on the 29th February this year did. But clearly that's not in common use. No, right now, most libsystemd.so libraries have headers saying "you'll need to load liblz4.so, liblzma.so and libzstd before you can load me!", so liblzma.so gets loaded for the logging functions that sshd doesn't use, so the distro maintainers of sshd can add 1 line instead of 10 to notify systemd that sshd is ready.

They just added an example to the documentation[0] of how to implement the sd_notify protocol without linking to libsystemd, so a little bit of discarding systemd (or at least parts of it) does seem to be part of the solution.

[0] https://github.com/systemd/systemd/pull/32030/files

I think this analysis is more interesting if you consider these two events in particular:

2024-02-29: On GitHub, @teknoraver sends pull request to stop linking liblzma into libsystemd.[1]

2024-03-20: The attacker is now a co-contributor for a patchset proposed to the Linux kernel, with the patchset adding the attacker as a maintainer and mirroring activity with xz-utils.

A theory is that the attacker saw the sshd/libsystemd/xz-utils vector as closing soon with libsystemd removing its dependency on xz-utils. When building a Linux kernel image, the resulting image is compressed by default with gzip [3], but can also be optionally compressed using xz-utils (amongst other compression utilities). There's a lot of distributions of Linux which have chosen xz-utils as the method used to compress kernel images, particularly embedded Linux distributions.[4] xz-utils is even the recommended mode of compression if a small kernel build image is desired.[5] If the attacker can execute code during the process of building a new kernel image, they can cause even more catastrophic impacts than targeting sshd. Targeting sshd was always going to be limited due to targets not exposing sshd over accessible networks, or implementing passive optical taps and real time behavioural analysis, or receiving real time alerts from servers indicative of unusual activity or data transfers. Targeting the Linux kernel would have far worse consequences possible, particularly if the attacker was targeting embedded systems (such as military transport vehicles [6]) where the chance of detection is reduced due to lack of eyeballs looking over it.

[1] https://github.com/systemd/systemd/pull/31550

[2] https://lkml.org/lkml/2024/3/20/1004

[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...

[4] https://github.com/search?q=CONFIG_KERNEL_XZ%3Dy&type=code

[5] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...

[6] https://linuxdevices.org/large-military-truck-runs-embedded-...