esm.sh CDN service has JS Template Literal Injection in CSS-to-JavaScript

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2025-65026: 0.51% estimated exploitation activity in the next 30 days; percentile 43.89 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The esm.sh CDN service contains a Template Literal Injection vulnerability (CWE-94) in its CSS-to-JavaScript module conversion feature. When a CSS file is requested with the ?module query parameter, esm.sh converts it to a JavaScript module by embedding the CSS content directly into a template literal without proper sanitization. An attacker can inject malicious JavaScript code using ${...} expressions within CSS files, which will execute when the module is imported by victim applications. This enables Cross-Site Scripting (XSS) in browsers and Remote Code Execution (RCE) in Electron applications. Root Cause: The CSS module conversion logic (router.go:1112-1119) performs incomplete sanitization - it only checks for backticks (\) but fails to escape template literal expressions (${...}), allowing arbitrary JavaScript execution when the CSS content is inserted into a template literal string. Details File: server/router.go Lines: 1112-1119 When CSS does not contain backticks,…

Published by the source

19 Nov 2025, 20:31 UTC

Last modified by the source

27 Nov 2025, 08:30 UTC

Source last checked

26 Oct 2026, 15:13 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-hcpf-qv9m-vfgp

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# Patch Next advisory brief: CVE-2025-65026

Advisory: esm.sh CDN service has JS Template Literal Injection in CSS-to-JavaScript
IDs: CVE-2025-65026, GHSA-hcpf-qv9m-vfgp
Record: https://patchnext.com/advisories/cve-2025-65026 (revision 1, source checked 26 Oct 2026, 15:13 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/esm-dev/esm.sh 0.0.0-20251118065157-87d2f6497574. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/esm-dev/esm.sh: affected < 0.0.0-20251118065157-87d2f6497574; fixed in 0.0.0-20251118065157-87d2f6497574

## Suggested inspection (read-only)
- Go github.com/esm-dev/esm.sh: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/esm-dev/esm.sh.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-hcpf-qv9m-vfgp (GitHub-reviewed advisory GHSA-hcpf-qv9m-vfgp lists affected ranges: Go github.com/esm-dev/esm.sh >=0 <0.0.0-20251118065157-87d2f6497574)

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