CVE Vulnerabilities

CVE-2021-39135

UNIX Symbolic Link (Symlink) Following

Published: Aug 31, 2021 | Modified: Nov 07, 2023
CVSS 3.x
7.8
HIGH
Source:
NVD
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS 2.x
4.4 MEDIUM
AV:L/AC:M/Au:N/C:P/I:P/A:P
RedHat/V2
RedHat/V3
8.1 IMPORTANT
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
Ubuntu
MEDIUM

@npmcli/arborist, the library that calculates dependency trees and manages the node_modules 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 projects node_modules folder. If the node_modules 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 node_modules symbolic link would have to be employed. 1. A preinstall script could replace node_modules 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. This is patched in @npmcli/arborist 2.8.2 which is included in npm v7.20.7 and above. For more information including workarounds please see the referenced GHSA-gmw6-94gg-2rc2.

Weakness

The product, when opening a file or directory, does not sufficiently account for when the file is a symbolic link that resolves to a target outside of the intended control sphere. This could allow an attacker to cause the product to operate on unauthorized files.

Affected Software

Name Vendor Start Version End Version
Npm Npmjs * 7.20.7 (excluding)
Npm Ubuntu bionic *
Npm Ubuntu hirsute *
Npm Ubuntu impish *
Npm Ubuntu kinetic *
Npm Ubuntu lunar *
Npm Ubuntu mantic *
Npm Ubuntu trusty *
Npm Ubuntu upstream *
Npm Ubuntu xenial *

Potential Mitigations

  • Follow the principle of least privilege when assigning access rights to entities in a software system.
  • Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.

References