Ensuring Yocto System Security: How to Detect and Mitigate SSH Backdoors via XZ LibLZMA

Homepage Ensuring Yocto System Security: How to Detect and Mitigate SSH Backdoors via XZ LibLZMA

In recent developments, the xz utility and its underlying liblzma library, essential components for Linux compression, have been identified as compromised.

This alarming revelation came from discovering a sophisticated supply chain attack aimed at introducing a backdoor in SSH, potentially allowing unauthorized remote access.

This article explains the risks, the versions affected, and how you can protect your systems, with a special focus on the Yocto Project, where Witekio, a Yocto Gold Member, plays a pivotal role in ensuring security and reliability for its hundreds of Yocto-based clients a year.

The XZ LibLZMA Attack Explained:

A highly coordinated attack targeted versions 5.6.0 and 5.6.1 of liblzma, a library used for data compression in the Linux ecosystem.

The intent was to inject a backdoor within SSH functionalities, thus compromising the integrity and security of affected systems.

Fortunately, the open-source community quickly identified and mitigated the threat before it could become widespread.

However, distributions on the cutting edge, like Arch Linux, found themselves at risk.

Is Your Yocto Build Safe?

For those utilizing the Yocto Project, the risk is minimal unless you engage in practices that integrate bleeding-edge or unstable releases.

The mainstream Yocto builds typically do not incorporate such recent library versions, but vigilance is crucial. Developers incorporating modules and dependencies that fetch updates outside standard repositories should be particularly cautious.

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How to Check for Compromised Systems:

To safeguard your infrastructure, it’s imperative to perform regular checks and updates.

A useful tool for this is the xz_liblzma_check script developed by Witekio engineer Brandon Lin, available on GitHub.

This script scans executables in /usr/bin/ or any specified directory to detect any linkage to the compromised liblzma versions, thus helping you identify and mitigate risks swiftly.

Witekio’s Role in Enhancing Security:

As a Yocto Gold Member, Witekio is exceptionally positioned to support device makers in securing their embedded systems and IoT devices.

Our expertise spans across embedded architecture, security enhancements, and comprehensive IoT solutions.

Whether you need assistance in optimizing your Yocto builds, implementing robust security measures, or tailoring your embedded applications, Witekio is your trusted partner.

We ensure that your projects not only meet but exceed industry standards for security and performance.


The recent supply chain attack on liblzma underscores the continuous need for vigilance in software security, especially in embedded and IoT ecosystems.

We encourage all developers and system administrators to update their systems regularly, utilize the xz_liblzma_check tool, and reach out to Witekio for any specialized support in embedded systems development and security.

Alternatively –if you have an in-house dev team, check out our off-the-shelf Linux tools (The Embedded Kit) for maintenance and testing.

Want to talk to our team about your device security?

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Georgie Ryan Casling - Content Manager
01 May 2024