6.1

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2025-65026

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

esm.sh is a nobuild content delivery network(CDN) for modern web development. Prior to version 136, 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. This issue has been patched in version 136.

(GitHub Advisory)

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CVE-2025-65026

CVE-2025-65026:

6.1

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
github.com/esm-dev/esm.sh	go	< 0.0.0-20251118065157-87d2f6497574	0.0.0-20251118065157-87d2f6497574

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability is a template literal injection in the esm.sh CDN service, specifically within the feature that converts CSS to a JavaScript module. The provided description and the fixing commit 87d2f6497574bf4448641a5527a3ac2beba5fd6c clearly point to the esmRouter function in server/router.go as the location of the vulnerable code. The patch shows the removal of a code block that directly wrote CSS content into a JavaScript template literal without proper sanitization. The vulnerable code path was taken when the CSS content did not contain a backtick. An attacker could exploit this by crafting a CSS file containing a malicious JavaScript payload within a ${...} expression. The fix involves always JSON-encoding the CSS content before embedding it in the JavaScript response, thus neutralizing the injection vector. Therefore, esmRouter is the vulnerable function that would appear in a runtime profile during exploitation.

Vulnerable functions

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WAF Protection Rules

WAF Rule

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Reasoning

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