CVE-2025-65026: esm.sh CDN service has JS Template Literal Injection in CSS-to-JavaScript

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.