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

> Attackers can inject JavaScript via CSS files served by esm.sh, leading to XSS in browsers or RCE in Electron apps.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 19 Nov 2025
- **Updated:** 20 Nov 2025
- **Also known as:** GHSA-hcpf-qv9m-vfgp, GO-2025-4139

## What is CVE-2025-65026?

CVE-2025-65026 is a medium-severity code injection vulnerability in esm-dev esm.sh, published on 19 Nov 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

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.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation), CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2025-65026?

3 open source packages ship an affected version, including github.com/esm-dev/esm.sh. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/esm-dev/esm.sh` | Go | All versions | 0.0.0-20251118065157-87d2f6497574 |
| `github.com/esm-dev/esm.sh` | Go | All versions | 0.0.0-20251118065157-87d2f6497574 |
| `github.com/esm-dev/esm.sh` | Go | All versions | 0.0.0-20251118065157-87d2f6497574 |

Products: Esm Esm.sh.

## How do I fix CVE-2025-65026?

Upgrade github.com/esm-dev/esm.sh to 0.0.0-20251118065157-87d2f6497574 or later.

## Is CVE-2025-65026 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-65026 exists.

## Other vulnerabilities in esm-dev esm.sh

- [CVE-2025-50180](https://insights.sbomify.com/CVE-2025-50180/): esm.sh is vulnerable to full-response SSRF (high 8.7)
- [CVE-2026-27730](https://insights.sbomify.com/CVE-2026-27730/): esm.sh has SSRF localhost/private-network bypass in `/http(s)` module route (high 8.6)
- [CVE-2025-65025](https://insights.sbomify.com/CVE-2025-65025/): esm.sh CDN service has arbitrary file write via tarslip (high 8.2)
- [CVE-2026-23644](https://insights.sbomify.com/CVE-2026-23644/): esm.sh has path traversal in `extractPackageTarball` that enables file writes from malicious packages (high 7.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-65026 and fix it if it is affected.

What it is: CVE-2025-65026 is a medium-severity code injection vulnerability in esm-dev esm.sh, published on 19 Nov 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-65026 exists.

Affected packages and fixed versions:
- github.com/esm-dev/esm.sh (Go): affected all versions; fixed in 0.0.0-20251118065157-87d2f6497574
- github.com/esm-dev/esm.sh (Go): affected all versions; fixed in 0.0.0-20251118065157-87d2f6497574
- github.com/esm-dev/esm.sh (Go): affected all versions; fixed in 0.0.0-20251118065157-87d2f6497574

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-65026/ (Markdown: https://insights.sbomify.com/CVE-2025-65026/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-65026
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-65026
- OSV: https://osv.dev/vulnerability/CVE-2025-65026

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-65026/
Summaries are generated and may contain mistakes; the official description above is the record.