# CVE-2026-120421: Eclipse Mojarra reflected XSS in URL client window mode

Source: https://junglewise.ai/threats/cve-2026-120421-in-eclipse-mojarra-versions-2-2-0-through-4-0-28-4-1-0-through-4  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-04. Updated: 2026-11-04  
License: CC BY 4.0 with a link back

CVE-2026-120421 · Severity: medium · CVSS 6.1 · Published 2026-11-04

Eclipse Mojarra is a Java framework for building web applications. When URL client window mode is enabled and `h:button` components are used, an attacker can inject malicious JavaScript through a crafted URL parameter. The injected script runs in the victim's browser when they click the button, allowing session hijacking, credential theft, or malware distribution.

Vendors: [Eclipse](https://junglewise.ai/threats/vendors/eclipse).

## Quick answers

**Is CVE-2026-120421 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-120421 being exploited in the wild.

**How severe is CVE-2026-120421?** Medium severity, with a CVSS score of 6.1, published 4 November 2026.

**Which products and versions are affected?** Eclipse Mojarra 2.2.0 through 4.0.28, 4.1.0 through 4.1.19, 5.0.0-M1 through 5.0.0-M11.

**Is there a fix for CVE-2026-120421?** Yes: fixed in 4.0.29, 4.1.20, 5.0.0-M12. Until then: Do not enable URL client window mode (keep `jakarta.faces.CLIENT_WINDOW_MODE` at its default `none`). Alternatively, validate the `jfwid` and `jakarta.faces.ClientWindow` parameters using a servlet filter or reverse proxy with a character whitelist such as `[A-Za-z0-9_:.-]`, or replace `h:button` with `h:link` on affected pages.</anigation>
<parameter name="timeline">[{"kind":"disclosed","at":"2026-11-04"}] Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-120421 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-120421?** Check whether you run Eclipse Mojarra at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in 4.0.29, 4.1.20, 5.0.0-M12

Do not enable URL client window mode (keep `jakarta.faces.CLIENT_WINDOW_MODE` at its default `none`). Alternatively, validate the `jfwid` and `jakarta.faces.ClientWindow` parameters using a servlet filter or reverse proxy with a character whitelist such as `[A-Za-z0-9_:.-]`, or replace `h:button` with `h:link` on affected pages.</anigation>
<parameter name="timeline">[{"kind":"disclosed","at":"2026-11-04"}]

## Technical details

The vulnerability is a reflected cross-site scripting (CWE-79) in the client window ID parameter handling. When URL client window mode is active, the `jfwid` or `jakarta.faces.ClientWindow` request parameter is appended to generated URLs without URL-encoding. The `h:button` renderer then includes this URL in a JavaScript string literal without escaping, allowing JavaScript injection. With CSP nonce enabled, the injected script executes on page load inside the nonce-protected script element, bypassing Content Security Policy protections.

## Affected products

- Eclipse Mojarra 2.2.0 through 4.0.28, 4.1.0 through 4.1.19, 5.0.0-M1 through 5.0.0-M11

## References

- [https://gitlab.eclipse.org/security/cve-assignment/-/work_items/536](https://gitlab.eclipse.org/security/cve-assignment/-/work_items/536)
- [https://gitlab.eclipse.org/security/vulnerability-reports/-/work_items/1332](https://gitlab.eclipse.org/security/vulnerability-reports/-/work_items/1332)