Note: This Rapid Response article has been written with AI assistance. Acknowledgments: Special thanks to Jevon Ang, Michael Elford, Jordan Sexton, Armelle French, Stephanie Fairless, Juzzy Allen, Ryan Dowd, Chad Hudson, Lindon Wass, James Maclachlan, James Northey, Josh Kiriakoff, Jai Minton, and Max Rogers for their contributions to this investigation and response. TL;DR: Huntress has observed active exploitation of a supply chain compromise targeting the axios npm package -- one of the most widely used JavaScript libraries, with over 100 million weekly downloads. The attack delivered a cross-platform Remote Access Trojan (RAT) to macOS, Windows, and Linux systems via a malicious dependency injected into backdoored axios releases. Organizations should immediately audit their dependencies for axios@1.14.1 or axios@0.30.4, treat any system that installed either version as compromised, and follow the remediation guidance below. Background On March 31, 2026, a coordinated supply chain attack was executed against the axios npm package. An attacker compromised the npm credentials of the lead maintainer account (jasonsaayman) and manually published two backdoored releases: axios@1.14.1 (tagged latest) and axios@0.30.4 (tagged legacy). These versions introduced a phantom dependency -- plain-crypto-js@4.2.1 ... a package that had not existed before that day and is never actually imported by axios code. Its sole purpose was to execute a postinstall script that drops and runs a cross-platform RAT targeting macOS, Windows, and Linux. axios is a promise-based HTTP client used extensively across the JavaScript and Node.js ecosystem. It is a transitive dependency for countless packages, CI/CD pipelines, developer workstations, and production applications worldwide. The scope of this compromise is significant: any environment that ran npm install and resolved to axios@1.14.1 or axios@0.30.4 during the approximately three-hour exposure window may have executed the malicious payload automatically with no user interaction required. The malicious versions were published during overnight hours (just after midnight UTC,