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XZ backdoor in a nutshell (lemmy.zip)

submitted 8 months ago by [email protected] to c/[email protected]

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[–] [email protected] 6 points 8 months ago* (last edited 7 months ago) (2 children)

I am not a security expert, but the scenario they describe sounds exactly like authentication bypass to a layman like me.

According to https://www.youtube.com/watch?v=jqjtNDtbDNI the software installs a malicious library that overwrite the signature verification function of ssh.

I was wondering if the bypass function was designed to be slightly less resource intensive, it probably won't be discovered and will be shipped to production.

Also I have mixed feeling about dynamic linking, on the one hand, it allows projects like harden malloc to easily integrate into the system, on the other hand, it also enables the attacker to hijack the library in a similar fashion.

EDIT: This is a remote code execution exploit, not authentication bypass. The payload is sent as an authentication message and will be executed by the compromised authentication function.

This means:

the payload will be executed as root, since sshd run as root.
the payload will leave no trace in login log.

So this is much worse than ssh authentication bypass.

[–] [email protected] 6 points 8 months ago* (last edited 8 months ago)

5.6.1 in fact made it less resources-intensive, but the distro happened to not have updated yet when Freund discovered the backdoor.

[–] [email protected] 2 points 8 months ago (1 children)

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.

[–] [email protected] 2 points 8 months ago* (last edited 7 months ago)

~~Yeah, but the malicious code replaces the ssh signature verification function to let it allow a specific signature. Hence attacker, with the key, can ssh into any system without proper authentication by ssh.~~

~~This kind of describes authentication by-pass, not just remote code execution...~~

EDIT: it is remote code execution, see the edit of parent comment.