In this article, we analyze XZ backdoor behavior inside OpenSSH, after it has achieved RSA-related function hook.
XZ Utils cyberattack likely not an isolated incident
Kaspersky analysis of the backdoor recently found in XZ, which is used in many popular Linux distributions and in OpenSSH server process.
The thwarted XZ Utils supply chain attack was years in the making. Now, clues suggest nation-state hackers were behind the persona that inserted the malicious code.
On March 29, right before Easter weekend, we received notifications about something unusual happening with the open-source project XZ Utils, which provides lossless data compression on virtually all Unix-like operating systems, including Linux.
The initial warning was sent to the Open Source Security mailing list sent by Andres Freund, who discovered that XZ Utils versions 5.6.0 and 5.6.1 are impacted by a backdoor. A few hours later, the US government’s CISA and OpenSSF warned about a critical problem: an installed XZ backdoored version could lead to unauthorized remote access.
Andres Freund published the existence of the xz attack on 2024-03-29 to the public oss-security@openwall mailing list. The day before, he alerted Debian security and the (private) distros@openwall list. In his mail, he says that he dug into this after “observing a few odd symptoms around liblzma (part of the xz package) on Debian sid installations over the last weeks (logins with ssh taking a lot of CPU, valgrind errors).”
At a high level, the attack is split in two pieces: a shell script and an object file. There is an injection of shell code during configure, which injects the shell code into make. The shell code during make adds the object file to the build. This post examines the shell script. (See also my timeline post.)
notes, honeypot, and exploit demo for the xz backdoor (CVE-2024-3094) - amlweems/xzbot
Malicious updates made to a ubiquitous tool were a few weeks away from going mainstream.
CVE-2024-3094 is the new hot one and it’s extremely critical; however, impact should be limited as most normal linux distros are unaffected. Here’s some stuff to know:
This is still a new situation. There is a lot we don't know. We don't know if there are more possible exploit paths. We only know about this one path. Please update your systems regardless. Unknown unknowns are safer than known unknowns.
This is a living document. Everything in this document is made in good faith of being accurate, but like I just said; we don't know much about what's going on.
esterday Andres Freund emailed oss-security@ informing the community of the discovery of a backdoor in xz/liblzma, which affected OpenSSH server (huge respect for noticing and investigating this). Andres' email is an amazing summary of the whole drama, so I'll skip that. While admittedly most juicy and interesting part is the obfuscated binary with the backdoor, the part that caught my attention – and what this blogpost is about – is the initial part in bash and the simple-but-clever obfuscation methods used there. Note that this isn't a full description of what the bash stages do, but rather a write down of how each stage is obfuscated and extracted.
This page is short for now but it will get updated as I learn more about the incident. Most likely it will be during the first week of April 2024.
The Git repositories of XZ projects are on git.tukaani.org.
xz.tukaani.org DNS name (CNAME) has been removed. The XZ projects currently don’t have a home page. This will be fixed in a few days.
Red Hat Information Risk and Security and Red Hat Product Security learned that the latest versions of the “xz” tools and libraries contain malicious code that appears to be intended to allow unauthorized access.
