The npm package datetime-fmt-xutil version 1.0.0 contains malicious code in its postinstall.js script. This script opens a TCP connection to a hardcoded IP address and pipes a shell to the remote endpoint, granting interactive shell access to an attacker. The malicious behavior executes unconditionally during npm install and uses fallback methods with bash and python3 to establish the reverse shell. Failures are reported via HTTP GET requests to the attacker's server. The package's legitimate date-formatting functionality is a cover for this reverse-shell payload.