The mchain-sdk package (version 4.2.5) is a malicious npm package that contains a postinstall hook executing a top-level async immediately-invoked function expression (IIFE) which base64-decodes a URL stored in its configuration. This URL points to an anonymous paste on jsonkeeper.com, from which it fetches attacker-controlled JavaScript code and executes it in a detached child node process. Additionally, the package's main module imports this malicious code immediately on load, triggering the payload even if npm install is run with --ignore-scripts. The package is a typosquatting repackage of the legitimate uhop/stream-chain library, designed to evade casual review by cloning its API surface and documentation. This results in full compromise of any system that installs or runs this package.

Systems with mchain-sdk version 4.2.5 installed or running are fully compromised, as the package executes remote attacker-controlled code with the privileges of the user running the package. This can lead to unauthorized access, data exfiltration, and control over the affected system. Secrets and keys stored on the compromised system are at risk and must be considered exposed.

There is no official patch or fix available for this malicious package. Immediate removal of the mchain-sdk package version 4.2.5 is required. However, removal alone may not eliminate all malicious artifacts or backdoors installed by the package. It is critical to rotate all secrets, keys, and credentials that were stored or used on the compromised system, using a separate, trusted device. Monitor for any suspicious activity and consider a full system rebuild if compromise is suspected.