CVE-2026-102657
esm.sh: web.NewHandler allows arbitrary file read via encoded dot-segment path traversal
esm.sh is a no-build content delivery network (CDN) for web development. Prior to server version 137_7, the documented web.NewHandler static file server in web/handler.go joins the URL-decoded r.URL.Path with Config.AppDir without verifying that the result remains inside the configured application directory. URL-encoded dot segments such as %2e%2e bypass the plain traversal redirect performed by Go's ServeMux, allowing an unauthenticated remote attacker to make the server open and return files outside Config.AppDir that are readable by the server process. The confirmed impact is file disclosure only, and the issue is reachable with Dev disabled. This issue is fixed in server version 137_7.
Fixes and workarounds
No remediation reported in collected sources.
Missing remediation information is not evidence that no patch exists.
Affected products and versions
| Product | Versions | Authority |
|---|---|---|
| esm.sh esm-dev |
< 137_7 (affected) | CNA: GitHub_M |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 3.1 / 7.5 high |
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N | CNA: GitHub_M |
Exploit evidence
No exploit evidence in collected sources. This is not proof of no exploitation.
References
- https://github.com/esm-dev/esm.sh/security/advisories/GHSA-g3c2-rjq2-c763CNA: GitHub_M · x_refsource_CONFIRM
- https://github.com/esm-dev/esm.sh/pull/1376CNA: GitHub_M · x_refsource_MISC
- https://github.com/esm-dev/esm.sh/commit/468b6b2a4b4dfec334cf6b33b01fcd4e5cd93bedCNA: GitHub_M · x_refsource_MISC
- https://github.com/esm-dev/esm.sh/commit/fc3b345e73aeaa0b7a05b6f27d91c05fdf5f9b53CNA: GitHub_M · x_refsource_MISC
- https://github.com/esm-dev/esm.sh/releases/tag/v137_7CNA: GitHub_M · x_refsource_MISC
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