But it would be nice to have a similar digram like OP’s to understand how exactly it does the RCE and implements the SSH backdoor. If we understand how, maybe we can take measures to prevent similar exploits in the future.
I think ideas about prevention should be more concerned with the social engineering aspect of this attack. The code itself is certainly cleverly hidden, but any bad actor who gains the kind of access as Jia did could likely pull off something similar without duplicating their specific method or technique.
I imagine if this attacker wasn’t in a rush to get the backdoor into the upcoming Debian and Fedora stable releases he would have been able to notice and correct the increased CPU usage tell and remain undetected.
Basically, if you have a patched SSH client with the right ED448 key you can have the gigged sshd on the other side run whatever commands you want. The demo just does id > /tmp/.xz but it could be whatever command you want.
Authentication bypass should give you interactive access. “I’m in” like. Remote code execution only allows you to run a command, without permanent access. You can use some RCE vulnerabilities to bypass authentication, but not all.
Under the right circumstances this interference could potentially enable a malicious actor to break sshd authentication and gain unauthorized access to the entire system remotely.
—Wikipedia, sourced to RedHat
Of course, the authentication bypass allows remote code execution.
From what I’ve heard so far, it’s NOT an authentication bypass, but a gated remote code execution.
There’s some discussion on that here: https://bsky.app/profile/filippo.abyssdomain.expert/post/3kowjkx2njy2b
But it would be nice to have a similar digram like OP’s to understand how exactly it does the RCE and implements the SSH backdoor. If we understand how, maybe we can take measures to prevent similar exploits in the future.
I think ideas about prevention should be more concerned with the social engineering aspect of this attack. The code itself is certainly cleverly hidden, but any bad actor who gains the kind of access as Jia did could likely pull off something similar without duplicating their specific method or technique.
Ideally you need a double-blind checking mechanism definitionally impervious to social engineering.
That may be possible in larger projects but I doubt you can do much in where you have very few maintainers.
I bet the lesson here for future attackers is: do not affect start-up time.
I imagine if this attacker wasn’t in a rush to get the backdoor into the upcoming Debian and Fedora stable releases he would have been able to notice and correct the increased CPU usage tell and remain undetected.
Somebody wrote a PoC for it: https://github.com/amlweems/xzbot#backdoor-demo
Basically, if you have a patched SSH client with the right ED448 key you can have the gigged sshd on the other side run whatever commands you want. The demo just does
id > /tmp/.xzbut it could be whatever command you want.deleted by creator
5.6.1 in fact made it less resources-intensive, but the distro happened to not have updated yet when Freund discovered the backdoor.
Authentication bypass should give you interactive access. “I’m in” like. Remote code execution only allows you to run a command, without permanent access. You can use some RCE vulnerabilities to bypass authentication, but not all.
deleted by creator
Here is an alternative Piped link(s):
https://www.piped.video/watch?v=jqjtNDtbDNI
Piped is a privacy-respecting open-source alternative frontend to YouTube.
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Of course, the authentication bypass allows remote code execution.