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Comment on How does the xz incident impacts the average user ? #xz

Jimmycrackcrack@lemmy.ml ⁨8⁩ ⁨months⁩ ago

I’m still confused exactly what the circumstances would be where this worked as the attacker intended. Would simply having the infected liblzma version on the system create the vulnerability or does something have to happen to invoke it and then what? What’s he chain of events that would have happened had this worked perfectly and gone undetected? I tried to read some of the more detailed analysis but the stuff went way over my head.

Also, what about Mac OS? Can the package create any vulnerability there if installed via homebrew as it’s reported to have done in some cases? Or is that environment also not right for it to work?

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neatchee@lemmy.world ⁨8⁩ ⁨months⁩ ago
Here’s how it was intended to work:

debian, fedora, or another RPM-based distribution updates references to liblzma to 5.6.x in their latest release

the package repository is updated (usually through automation) by getting the infected tarball and compiling it into an RPM which is added to the repo

if the package is built using glibc and the gnu linker, and for a system that uses systemd, the exploit is enabled during compilation of the x86-64 version of the package; otherwise the result is normal

when an application is installed that depends on liblzma, possibly during OS installation itself, the infected RPM package from the package repository is downloaded and installed

in this particular case, OpenSSH was the primary target; if the attacker wanted to, it could have targeted any web-facing service that uses liblzma such as OpenSSL + Apache/nginx, etc

when the OpenSSH server is started on an infected system, it loads the infected liblzma binary

the attacker starts an SSH connection to the infected server, having already known about the server or by scanning the internet for visible ssh servers

during creation of the SSH connection, one of the steps is to negotiate encryption using an RSA key. The attacker uses a specially formed RSA key only available to the attacker that also contains a chunk of code (the “payload”) that they want executed on the server

liblzma is utilized to compress data in transit; when the infected liblzma decompresses the RSA key on the server, the exploit recognizes the attacker’s special RSA key and executes the payload on the host system. Otherwise, the ssh session continues as normal
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- NeatNit@discuss.tchncs.de ⁨8⁩ ⁨months⁩ ago
  Thank you! I believe this is what the OP was asking, and it’s definitely what I wanted to know :)
  
  Do we know what the payload is?
  
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  - neatchee@lemmy.world ⁨8⁩ ⁨months⁩ ago
    Arbitrary. It could be whatever they wanted at any time
    
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