Node Version Manager (nvm) is a POSIX-compliant shell function for managing multiple node.js versions. In versions 0.27.0 through 0.40.8, when a project's .npmrc sets prefix, nvm use tells the user to run nvm use --delete-prefix, which runs npm config delete prefix and npm config delete globalconfig in the current directory without naming a config file. npm loads the project .npmrc before deciding which file to edit, so that file chooses the target: userconfig=~/.bashrc makes npm rewrite ~/.bashrc as ini (corrupting it), and location=global with globalconfig= leaves the chosen file at mode 0666, which on a shared machine lets another local user write to it. The attacker (the author of a cloned repository or archive, or a local user who can write a shared parent directory) chooses the file but not the bytes written, and no project code runs. Version 0.41.0 no longer lets a project .npmrc select which config file --delete-prefix edits.
Until upgrading, do not run nvm use --delete-prefix in an untrusted project directory; remove the prefix setting from your own npmrc files by hand instead.
Upgrade to nvm 0.41.0 or later.