decompress allows arbitrary hardlink creation during archive extraction

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.5 · CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-39243: 0.30% estimated exploitation activity in the next 30 days; percentile 22.95 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

decompress before 4.2.2 allows arbitrary hardlink creation during archive extraction, enabling file read disclosure and file corruption. When processing hardlink entries (type === 'link'), the x.linkname field from the archive is passed directly to fs.link() without validation (index.js line 113). An attacker can craft an archive with a hardlink entry whose linkname is an absolute path to any file on the same filesystem. This creates a hardlink inside the extraction directory that shares the same inode as the target file, enabling both reading and overwriting the original file's content. Hardlinks are limited to files on the same filesystem and cannot target directories.

Published by the source

10 Jul 2026, 00:31 UTC

Last modified by the source

13 Aug 2026, 14:41 UTC

Source last checked

26 Oct 2026, 13:01 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-jwp9-9v96-94mx

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-jwp9-9v96-94mx

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-39243

Advisory: decompress allows arbitrary hardlink creation during archive extraction
IDs: CVE-2026-39243, GHSA-jwp9-9v96-94mx
Record: https://patchnext.com/advisories/cve-2026-39243 (revision 2, source checked 26 Oct 2026, 13:01 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm decompress: affected <= 4.2.1

## Suggested inspection (read-only)
- `npm ls decompress --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on decompress.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-jwp9-9v96-94mx (OSV record GHSA-jwp9-9v96-94mx lists affected ranges: npm decompress >=0 <=4.2.1)
- Verified: https://github.com/advisories/GHSA-jwp9-9v96-94mx (GitHub-reviewed advisory GHSA-jwp9-9v96-94mx lists affected ranges: npm decompress >=0 <=4.2.1)

Commands are suggestions: review each one before running it.