The XZ Backdoor: A Wake-Up Call for Open-Source Software Supply Chains

What happened

The recent discovery of a sophisticated backdoor in the widely used open-source data compression library XZ (1) should be an alarm reminder of the critical need to secure our software supply chains.

What happened? A previously trusted GitHub contributor gradually gained control of the XZ project over two years before injecting malicious code (1). The backdoor allowed attackers to execute commands on systems running the compromised software. Five suspicious GitHub accounts helped vouch for the attacker's credibility (2).

Why it matters

This "insider threat" attack on open-source code is nearly unprecedented (1). Open-source software is a pillar of the digital economy, but projects often need more resources and overworked volunteer maintainers. Attackers exploited this to compromise a critical, widely-used component. If left undetected, the backdoor could have potentially led to breaches of countless downstream applications and systems, posing a significant threat to our digital infrastructure.

Potential supply chain impact

1. XZ is a widely used data compression library. Many applications and systems depend on XZ, so a backdoor in XZ could potentially compromise many downstream users. This is similar to how the SolarWinds hack impacted many organizations by compromising a widely used IT management tool.
2. The incident has been likened to "an insider threat in the open source ecosystem." Open source software is foundational to many software supply chains, so an 'insider threat' in open source could have wide-ranging supply chain implications.
3. There were attempts to include the compromised XZ version in the Debian, Fedora, and Ubuntu distributions. Had these attempts succeeded, the backdoor could have been distributed to many systems via standard software update mechanisms, compromising many software supply chains.

Prevention strategies

• Increase funding, resources, and oversight for critical open-source projects
• Establish review processes to verify code contributions, even from trusted sources
• Use software composition analysis tools to analyze open-source dependencies
• Foster a culture of healthy contribution and maintenance in open-source
• Create contingency plans for security incidents in key open-source components

The XZ incident should serve as a rallying point for government, industry, and the open-source community to unite and implement systemic improvements to the security and sustainability of the open-source software supply chain. Your active participation is crucial in this collective effort. Failing to act risks the integrity of the digital infrastructure we all depend on.

References

Sakellariadis, J. (2024, March 31). Thwarted supply-chain hack sets off alarm bells across DC. Politico. https://www.politico.com/news/2024/03/31/thwarted-supply-chain-hack-alarm-bells-00149877?cid=apn

Boehs, E. (2024, March 29). Everything I know about the XZ backdoor. https://boehs.org/node/everything-i-know-about-the-xz-backdoor