Netflix

Dependency Confusion Attacks Let Attackers Hijack Internal Library Names in Corporate Builds

A widespread supply chain risk allows attackers to publish packages with internal company names on public registries such as npm and PyPI, causing build systems to pull malicious versions instead of internal ones. The attack works because package managers treat multiple registries as a single list and select the highest version number, with no inherent priority for internal sources. Researcher Alex Birsan demonstrated the technique in February 2021 by registering names harvested from open repositories and error messages, successfully injecting packages into builds at Microsoft, Apple, PayPal, Shopify, Netflix, Tesla and Uber. The malicious code executes during installation because setup scripts and lifecycle hooks run with the privileges of the build agent, exposing environment variables, tokens and internal network access. Mitigation requires a single internal proxy repository that never mixes public responses for internal package names, scoped namespaces bound to private registries, lock files with content hashes, and disabling install scripts where possible. The technique remains effective against any organization that lists both internal and public registries in its build configuration.