Cybersecurity researchers have identified a significant vulnerability in legacy Python packages that could enable a supply chain compromise through domain takeover attacks. The issue was uncovered by ReversingLabs, which found problematic code in the bootstrap files of a build and deployment automation tool called "zc.buildout."
The vulnerability arises when the bootstrap script is executed, causing it to download and run an installation script for a package called Distribute from a legacy domain, python-distribute.org, which is currently available for purchase. This domain has been up for sale since 2014, presenting a risk if it is acquired by malicious actors.
Several packages on the Python Package Index (PyPI), including tornado, pypiserver, slapos.core, roman, xlutils, and testfixtures, utilize a bootstrap script that connects to this potentially dangerous domain. The script is part of an older bootstrap file that was designed to initialize the Buildout environment and support the installation of Distribute—a fork of the commonly used Setuptools package that has since become obsolete.
The problem stems from the fact that many packages continue to include the bootstrap script, which can either try to install Distribute by default or when specified by a command-line option. As the domain is unclaimed, attackers could exploit this setup to execute malicious code and potentially extract sensitive data.
While some affected packages have made efforts to remove the vulnerable bootstrap script, slapos.core still includes it in its current version. The presence of this outdated script poses an unnecessary attack surface, even though it cannot run on Python 3 without modifications. However, if developers inadvertently run the script, they may expose their systems to attacks.
The risk of domain takeover in software supply chains is not just theoretical. An example from 2023 involved the compromise of the npm package fsevents, where a bad actor took control of an unclaimed cloud resource to distribute malicious executables.
Vladimir Pezo, a researcher from ReversingLabs, emphasized that the vulnerability arises from a programming practice that fetches and executes code from a hard-coded domain, a behavior typically observed in malware. The continued existence of these vulnerable scripts highlights a failure to formally decommission the Distribute module, which leaves countless projects susceptible to potential cyberattacks.
In related news, HelixGuard revealed a malicious package on PyPI named "spellcheckers," which masqueraded as a tool for checking spelling errors but contained harmful code intended to connect to external servers for further payload downloads, thereby executing a remote access trojan (RAT). The package was uploaded on November 15, 2025, and had been downloaded nearly 1,000 times before it was removed.
This situation underscores the ongoing challenges in ensuring the security of software supply chains and the importance of maintaining vigilance against potential vulnerabilities.
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