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Arbitrary File Creation/Overwrite via insufficient symlink protection due to directory cache poisoning using symbolic links

High severity GitHub Reviewed Published Aug 31, 2021 in isaacs/node-tar • Updated Feb 7, 2024

Package

npm tar (npm)

Affected versions

>= 5.0.0, < 5.0.10
>= 6.0.0, < 6.1.9
>= 3.0.0, < 4.4.18

Patched versions

5.0.10
6.1.9
4.4.18

Description

Impact

Arbitrary File Creation, Arbitrary File Overwrite, Arbitrary Code Execution

node-tar aims to guarantee that any file whose location would be modified by a symbolic link is not extracted. This is, in part, achieved by ensuring that extracted directories are not symlinks. Additionally, in order to prevent unnecessary stat calls to determine whether a given path is a directory, paths are cached when directories are created.

This logic was insufficient when extracting tar files that contained two directories and a symlink with names containing unicode values that normalized to the same value. Additionally, on Windows systems, long path portions would resolve to the same file system entities as their 8.3 "short path" counterparts. A specially crafted tar archive could thus include directories with two forms of the path that resolve to the same file system entity, followed by a symbolic link with a name in the first form, lastly followed by a file using the second form. It led to bypassing node-tar symlink checks on directories, essentially allowing an untrusted tar file to symlink into an arbitrary location and subsequently extracting arbitrary files into that location, thus allowing arbitrary file creation and overwrite.

The v3 branch of node-tar has been deprecated and did not receive patches for these issues. If you are still using a v3 release we recommend you update to a more recent version of node-tar. If this is not possible, a workaround is available below.

Patches

6.1.9 || 5.0.10 || 4.4.18

Workarounds

Users may work around this vulnerability without upgrading by creating a custom filter method which prevents the extraction of symbolic links.

const tar = require('tar')

tar.x({
  file: 'archive.tgz',
  filter: (file, entry) => {
    if (entry.type === 'SymbolicLink') {
      return false
    } else {
      return true
    }
  }
})

Users are encouraged to upgrade to the latest patched versions, rather than attempt to sanitize tar input themselves.

Fix

The problem is addressed in the following ways, when comparing paths in the directory cache and path reservation systems:

  1. The String.normalize('NFKD') method is used to first normalize all unicode to its maximally compatible and multi-code-point form.
  2. All slashes are normalized to / on Windows systems (on posix systems, \ is a valid filename character, and thus left intact).
  3. When a symbolic link is encountered on Windows systems, the entire directory cache is cleared. Collisions related to use of 8.3 short names to replace directories with other (non-symlink) types of entries may make archives fail to extract properly, but will not result in arbitrary file writes.

References

@isaacs isaacs published to isaacs/node-tar Aug 31, 2021
Reviewed Aug 31, 2021
Published to the GitHub Advisory Database Aug 31, 2021
Published by the National Vulnerability Database Aug 31, 2021
Last updated Feb 7, 2024

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Local
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

EPSS score

0.130%
(49th percentile)

CVE ID

CVE-2021-37712

GHSA ID

GHSA-qq89-hq3f-393p

Source code

Credits

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