CVE-2026-23644: esm.sh has path traversal in `extractPackageTarball` that enables file writes from malicious packages

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-01-18 · updated 2026-06-17
Weakness: CWE-22

Description

esm.sh is a no-build content delivery network (CDN) for web development. Prior to Go pseeudoversion 0.0.0-20260116051925-c62ab83c589e, the software has a path traversal vulnerability due to an incomplete fix. `path.Clean` normalizes a path but does not prevent absolute paths in a malicious tar file. Commit https://github.com/esm-dev/esm.sh/commit/9d77b88c320733ff6689d938d85d246a3af9af16, corresponding to pseudoversion 0.0.0-20260116051925-c62ab83c589e, fixes this issue.

Affected products

esm-dev esm.sh: before 136 — fixed in 136

How to fix

Upgrade to a fixed version: esm-dev esm.sh 136. Check the vendor advisory for mitigations.

References

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