The npm package 'checkout-storybook-default' version 35.5.1 contains malicious code that, upon requiring the package, loads a polyfill script which reconstructs command-and-control hostnames at runtime. It downloads an opaque binary payload over HTTPS using a spoofed user-agent and can fallback to a covert DNS-TXT channel. The payload is saved to a hidden cache path with a decoy filename, given executable permissions, and executed detached from the parent process. The malware includes sandbox evasion techniques and uses marker files to prevent repeated execution. This behavior is unrelated to the package's stated functionality.