MAL-2026-5526 Malicious code in chai-check-error (npm)

[email protected] impersonates the legitimate chaijs/check-error utility (copied README, author metadata, repository URL, and exported API surface) and adds a malicious payload. package.json declares "postinstall": "node index.js", and index.js calls _initMsgCache() at module top level so the same code path also fires on every require(). _initMsgCache derives an AES-256-CBC key/IV from a hardcoded byte array _d mixed via a _sbox(0x9E3779B1,...) routine, decrypts a 165-byte ciphertext into an HTTPS URL, fetches that URL with require('https').get(...), parses the JSON response, and executes the cookie field as JavaScript through new Function('require', mod)(require). The destination URL is intentionally obfuscated and the surrounding comments frame the routine as a benign "internal message cache" / "locale-aware message formatting" feature, but getMessage never reads _msgCache — the cache framing is cover-story. Any developer who installs this package — whether intentionally or by confusing it with chai's check-error — runs arbitrary attacker-controlled JavaScript under their Node process at install time and again on every import.