Versions of the npm CLI prior to 6.13.4 are vulnerable to an Arbitrary File Overwrite. It fails to prevent existing globally-installed binaries to be overwritten by other package installations. For example, if a package was installed globally and created a serve binary, any subsequent installs of packages that also create a serve binary would overwrite the previous serve binary. This behavior is still allowed in local installations and also through install scripts. This vulnerability bypasses a user using the --ignore-scripts install option.
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.