On March 31, 2026, axios — one of the most widely downloaded HTTP client libraries in the JavaScript ecosystem — was backdoored on npm. Malicious versions were live from approximately 00:21 UTC to 03:15 UTC; any npm install or npm update that ran against the registry during that window and resolved to the compromised version executed a postinstall script dropping a cross-platform Remote Access Trojan on the host.
The RAT harvests system credentials, browser session tokens, developer API keys, and .env files, then establishes a persistent C2 channel. The attack is registry-level — any package manager that pulls from npm and executes postinstall hooks was affected, not just the npm CLI.
The window directly overlapped with the release of @anthropic-ai/claude-code v2.1.88 (which also shipped with an accidental source map leak that day), meaning developer machines running a Claude Code install or update during the overlap were simultaneously exposed to the axios RAT payload and the source intelligence enabling precision jailbreak research against Claude Code's internals.
Immediate action: Audit CI/CD logs and local shell history for any npm install or update between 00:21–03:15 UTC on March 31, 2026. If runs occurred without a lockfile or with a caret dependency on axios, treat the host as compromised and begin incident response. Check for persistence mechanisms and unauthorized outbound connections.