EUVD-2026-265722

fkie_cve-2025-59342

esm.sh is a nobuild content delivery network(CDN) for modern web development. In 136 and earlier, a path-traversal flaw in the handling of the X-Zone-Id HTTP header allows an attacker to cause the application to write files outside the intended storage location. The header value is used to build a filesystem path but is not properly canonicalized or restricted to the application’s storage base directory. As a result, supplying ../ sequences in X-Zone-Id causes files to be written to arbitrary directories. Version 136.1 contains a patch.

GHSA-g2h5-cvvr-7gmw — esm.sh has arbitrary file write via path traversal in `X-Zone-Id` header

Affected: Go: github.com/esm-dev/esm.sh

## Summary

A path-traversal flaw in the handling of the `X-Zone-Id` HTTP header allows an attacker to cause the application to write files outside the intended storage location. The header value is used to build a filesystem path but is not properly canonicalized or restricted to the application’s storage base directory. As a result, supplying `../` sequences in `X-Zone-Id` causes files to be written to arbitrary directories (example observed: `~/.esmd/modules/transform/<id>/` instead of `~/.esmd/storage/modules/transform`).

**Severity:** Medium

**Component / Endpoint:**

`POST /transform` — handling of `X-Zone-Id` header

The vulnerable code is in https://github.com/esm-dev/esm.sh/blob/main/server/router.go#L116 and https://github.com/esm-dev/esm.sh/blob/main/server/router.go#L411

**Impact:** Arbitrary file creation / overwrite outside intended storage directory (file write to attacker-controlled path). Possible remote code execution, persistence, tampering with application files, or facilitating further path-traversal attacks.

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## Proof of Concept (POC)

Request (attacker-supplied `X-Zone-Id` contains path traversal):

``` POST /transform HTTP/1.1 Host: localhost:8888 User-Agent: Den/8.7.1 Accept: */* Connection: keep-alive Referer: http://localhost:9999/ Content-Type: application/json X-Zone-Id: ../../modules/transform/c245626ef6ca0fd9ee37759c5fac606c6ec99daa/ Content-Length: 325

{ "filename": "example2.js", "lang": "js", "code": "console.log('hello');",…

openSUSE-SU-2025:15576-1 — govulncheck-vulndb-0.0.20250924T192141-1.1 on GA media

govulncheck-vulndb-0.0.20250924T192141-1.1 on GA media

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EUVD-2026-265722

fkie_cve-2025-59342

GHSA-g2h5-cvvr-7gmw — esm.sh has arbitrary file write via path traversal in `X-Zone-Id` header

openSUSE-SU-2025:15576-1 — govulncheck-vulndb-0.0.20250924T192141-1.1 on GA media