esm.sh CDN service has arbitrary file write via tarslip

Exploitation

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

CVSS

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

EPSS

• CVE-2025-65025: 0.57% estimated exploitation activity in the next 30 days; percentile 47.28 (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.

Summary The esm.sh CDN service is vulnerable to a Path Traversal (CWE-22) vulnerability during NPM package tarball extraction. An attacker can craft a malicious NPM package containing specially crafted file paths (e.g., package/../../tmp/evil.js). When esm.sh downloads and extracts this package, files may be written to arbitrary locations on the server, escaping the intended extraction directory. Uploading files containing ../ in the path is not allowed on official registries (npm, GitHub), but the X-Npmrc header allows specifying any arbitrary registry. By setting the registry to an attacker-controlled server via the X-Npmrc header, this vulnerability can be triggered. Details file: server/npmrc.go line: 552-567 The code uses path.Join(pkgDir, name), which normalizes the path and allows sequences like ../../ to escape the intended package directory. PoC Test On - esm.sh Official Docker Image (latest version) - python 3.11 - flask (for attacker registry server) Step 1. Create…

Published by the source

19 Nov 2025, 20:30 UTC

Last modified by the source

27 Nov 2025, 08:29 UTC

Source last checked

26 Oct 2026, 15:13 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-h3mw-4f23-gwpw

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# Patch Next advisory brief: CVE-2025-65025

Advisory: esm.sh CDN service has arbitrary file write via tarslip
IDs: CVE-2025-65025, GHSA-h3mw-4f23-gwpw
Record: https://patchnext.com/advisories/cve-2025-65025 (revision 1, source checked 26 Oct 2026, 15:13 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/esm-dev/esm.sh 0.0.0-20251117232647-9d77b88c3207. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/esm-dev/esm.sh: affected < 0.0.0-20251117232647-9d77b88c3207; fixed in 0.0.0-20251117232647-9d77b88c3207

## Suggested inspection (read-only)
- Go github.com/esm-dev/esm.sh: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/esm-dev/esm.sh.
- 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://github.com/advisories/GHSA-h3mw-4f23-gwpw (GitHub-reviewed advisory GHSA-h3mw-4f23-gwpw lists affected ranges: Go github.com/esm-dev/esm.sh >=0 <0.0.0-20251117232647-9d77b88c3207)

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