decimal-format-utilsnpm

The postinstall script scripts/sync-peer.cjs runs npm pack [email protected] (or whatever version is configured via BACKUP_TARGET_VERSION/BACKUP_PAYLOAD_SPEC), extracts the resulting tarball, overwrites every file of the installed v1.0.0 package in place via fs.cpSync over the package root, and then require()s the replaced index.js and awaits from_str(). The effect is that npm install [email protected] executes code from a different, publisher-mutable version at install time, bypassing lockfile pinning and giving the publisher a live remote code execution channel into every install. The package additionally impersonates the big.js maintainer: package.json sets author: Michael Mclaughlin and repository.url: https://github.com/MikeMcl/big.js.git, and the README falsely claims the package is pulled in automatically as a dependency of [email protected]. big.js declares no such dependency. The impersonation appears designed to lure installers into trusting an unrelated publisher whose postinstall then executes arbitrary fetched code.

Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.