CVE-2026-102657

esm.sh: web.NewHandler allows arbitrary file read via encoded dot-segment path traversal

Published Nov 6, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-g3c2-rjq2-c763 esm.sh: web.NewHandler allows arbitrary file read via encoded dot-segment path traversal
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Esm-dev
Esm-dev esmsh
Vendors & Products Esm-dev
Esm-dev esmsh
Type Values Removed Values Added
Description 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.
Title esm.sh: web.NewHandler allows arbitrary file read via encoded dot-segment path traversal
Weaknesses CWE-22
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Nov 11, 2026, 3:30 AM
Reserved
Sep 29, 2026, 3:56 PM
Status
Deferred
Published
Nov 6, 2026, 9:17 PM
Modified
Nov 11, 2026, 5:19 AM