@npmcli/arborist, the library that calculates dependency trees and manages the nodemodules folder hierarchy for the npm command line interface, aims to guarantee that package dependency contracts will be met, and the extraction of package contents will always be performed into the expected folder. This is, in part, accomplished by resolving dependency specifiers defined in package.json manifests for dependencies with a specific name, and nesting folders to resolve conflicting dependencies. When multiple dependencies differ only in the case of their name, Arborist's internal data structure saw them as separate items that could coexist within the same level in the nodemodules hierarchy. However, on case-insensitive file systems (such as macOS and Windows), this is not the case. Combined with a symlink dependency such as file:/some/path, this allowed an attacker to create a situation in which arbitrary contents could be written to any location on the filesystem. For example, a package pwn-a could define a dependency in their package.json file such as "foo": "file:/some/path". Another package, pwn-b could define a dependency such as FOO: "file:foo.tgz". On case-insensitive file systems, if pwn-a was installed, and then pwn-b was installed afterwards, the contents of foo.tgz would be written to /some/path, and any existing contents of /some/path would be removed. Anyone using npm v7.20.6 or earlier on a case-insensitive filesystem is potentially affected. This is patched in @npmcli/arborist 2.8.2 which is included in npm v7.20.7 and above.

Impact

Arbitrary File Creation, Arbitrary File Overwrite, Arbitrary Code Execution

@npmcli/arborist, the library that calculates dependency trees and manages the nodemodules folder hierarchy for the npm command line interface, aims to guarantee that package dependency contracts will be met, and the extraction of package contents will always be performed into the expected folder.

This is accomplished by extracting package contents into a project's nodemodules folder.

If the nodemodules folder of the root project or any of its dependencies is somehow replaced with a symbolic link, it could allow Arborist to write package dependencies to any arbitrary location on the file system.

Note that symbolic links contained within package artifact contents are filtered out, so another means of creating a nodemodules symbolic link would have to be employed.

1. A preinstall script could replace nodemodules with a symlink. (This is prevented by using --ignore-scripts.) 2. An attacker could supply the target with a git repository, instructing them to run npm install --ignore-scripts in the root. This may be successful, because npm install --ignore-scripts is typically not capable of making changes outside of the project directory, so it may be deemed safe.

Patches

2.8.2 (included in npm v7.20.7 and above)

Workarounds

Do not run npm install on untrusted codebases, without first ensuring that the nodemodules directory in the project is not a symbolic link.

Fix

Prior to extracting any package contents, the nodemodules folder into which it is extracted is verified to be a real directory. If it is not, then it is removed.

Caveat: if you are currently relying on creating a symbolic link to the nodemodules folder in order to share dependencies between projects, then that will no longer be possible. Please use the npm link command, explicit file:... dependencies, and/or workspaces to share dependencies in a development environment.

An issue was discovered in an npm 5.7.0 2018-02-21 pre-release (marked as "next: 5.7.0" and therefore automatically installed by an "npm upgrade -g npm" command, and also announced in the vendor's blog without mention of pre-release status). It might allow local users to bypass intended filesystem access restrictions because ownerships of /etc and /usr directories are being changed unexpectedly, related to a "correctMkdir" issue.

A flaw was found in npm. This security issue occurs because the npm pack ignores root-level ".gitignore" and ".npmignore" file exclusion directives when run in a workspace or with a workspace flag (for example, --workspaces, --workspace=<name>). Anyone who has run 'npm pack' or 'npm publish' inside a workspace has published files into the npm registry they did not intend to include. This flaw exposes sensitive information to an unauthorized user or an attacker.