Summaryinfo

A vulnerability was found in capricorn86 happy-dom up to 20.8.8. It has been rated as problematic. This issue affects some unknown processing. Performing a manipulation results in insertion of sensitive information into sent data. This vulnerability is cataloged as CVE-2026-34226. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in capricorn86 happy-dom up to 20.8.8. It has been classified as problematic. This affects an unknown function. The manipulation with an unknown input leads to a insertion of sensitive information into sent data vulnerability. CWE is classifying the issue as CWE-201. The code transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor. This is going to have an impact on confidentiality. The summary by CVE is:

Happy DOM is a JavaScript implementation of a web browser without its graphical user interface. Versions prior to 20.8.9 may attach cookies from the current page origin (`window.location`) instead of the request target URL when `fetch(..., { credentials: "include" })` is used. This can leak cookies from origin A to destination B. Version 20.8.9 fixes the issue.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-34226 since 03/26/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1592 according to MITRE ATT&CK.

Upgrading to version 20.8.9 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch 68324c21d7b98f53f7bb5a7b3e185bda7106e751 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-16893). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Vendor

• capricorn86

Name

• happy-dom

Version

• 20.8.0
• 20.8.1
• 20.8.2
• 20.8.3
• 20.8.4
• 20.8.5
• 20.8.6
• 20.8.7
• 20.8.8

License

• open-source

Website

• Product: https://github.com/capricorn86/happy-dom/

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