Cybersecurity researchers have identified a supply chain vulnerability affecting multiple legacy Python packages on PyPI due to the continued inclusion of an outdated bootstrap script (bootstrap.py) associated with the zc.buildout build automation tool. This script attempts to fetch and execute an installation script for the Distribute package from the domain python-distribute.org, which has been defunct and up for sale since 2014. Distribute was a short-lived fork of Setuptools, created to address stagnation in Setuptools development but later merged back, rendering Distribute obsolete. The vulnerable bootstrap script either installs Distribute by default or when invoked with specific command-line options. Because the domain is currently unclaimed, an attacker could acquire it and serve malicious payloads to users who run the bootstrap script, enabling remote code execution and potential data theft. Although the script is written for Python 2 and not automatically executed during package installation, its presence in packages such as Tornado, pypiserver, slapos.core, roman, xlutils, and testfixtures creates an unnecessary attack surface. The risk is exacerbated by the fact that some packages, like slapos.core and Tornado's development versions, still include the vulnerable script. This vulnerability exemplifies the dangers of legacy code and unmaintained dependencies in software supply chains. The threat is supported by historical precedents, such as the 2023 npm fsevents domain takeover attack, which resulted in a critical CVE with a high severity score. Additionally, the discovery of malicious PyPI packages employing remote access trojans underscores the active threat landscape targeting Python ecosystems. While no known exploits targeting this specific vulnerability have been observed, the potential for supply chain compromise remains significant.

For European organizations, this vulnerability poses a tangible risk to software supply chain integrity, particularly for those relying on legacy Python packages that include the vulnerable bootstrap script. If an attacker acquires the python-distribute.org domain, they could serve malicious code during bootstrap script execution, leading to remote code execution on developer or build systems. This could result in the injection of backdoors or malware into software builds, compromising confidentiality, integrity, and availability of software products. The impact extends to development pipelines, continuous integration environments, and production deployments that depend on affected packages. Given the widespread use of Python in European enterprises, academia, and government, the risk of supply chain compromise could affect critical infrastructure, financial institutions, and technology companies. Furthermore, the presence of legacy Python 2 code in some environments may increase exposure, especially in organizations that have not fully migrated to Python 3. The potential for lateral movement and data exfiltration following initial compromise could amplify the damage. Although exploitation requires manual execution of the bootstrap script, social engineering or developer mistakes could trigger the attack. The latent risk also complicates vulnerability management and software audits, as the vulnerable code may be overlooked due to its legacy status.

European organizations should conduct thorough audits of their Python dependencies to identify any packages containing the vulnerable bootstrap.py script referencing python-distribute.org. Immediate steps include removing or updating affected packages to versions that have eliminated the bootstrap script or replaced it with secure alternatives. Developers should be educated about the risks of running legacy bootstrap scripts, especially those requiring Python 2, and discouraged from executing such scripts manually. Build and deployment pipelines should be reviewed to ensure no legacy bootstrap scripts are invoked. Organizations should implement strict supply chain security practices, including verifying package integrity via checksums and signatures, and employing tools that detect hard-coded external fetches from deprecated or untrusted domains. Monitoring for domain registrations of python-distribute.org and related domains can provide early warning of potential takeover attempts. Additionally, migrating all Python codebases to Python 3 reduces the risk of accidental execution of Python 2 scripts. Finally, organizations should consider adopting Software Bill of Materials (SBOM) practices to track dependencies and legacy components systematically.