CVE-2026-84129

Analyzed Analyzed - Analysis Complete

Firefox DOM Navigation Site Isolation Flaw

Publication date: 2026-09-01

Last updated on: 2026-09-03

Assigner: Mozilla Corporation

Description

Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-09-01

Last Modified

2026-09-03

Generated

2026-09-21

AI Q&A

2026-09-01

EPSS Evaluated

2026-09-20

NVD

CVE-2026-84129

EUVD

EUVD-2026-69078

Affected Vendors & Products

Vendor	Product	Version / Range
mozilla	firefox	to 153.2.0 (exc)
mozilla	firefox	From 154.0.0 (inc) to 155.0.0 (exc)
mozilla	thunderbird	to 153.2.0 (exc)
mozilla	thunderbird	From 154.0 (inc) to 155.0 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-346	The product does not properly verify that the source of data or communication is valid.

Attack-Flow Graph

Executive Summary

This is a site isolation issue in Firefox's DOM Navigation component. It allows potential data leakage between different websites due to improper separation of site contexts. The vulnerability was patched in Firefox 155 and Firefox ESR 153.2.

Detection Guidance

This vulnerability is specific to Firefox 155 and Firefox ESR 153.2. To detect it, check your Firefox version using commands like 'firefox --version' or 'about:support' in Firefox. If your version is below 155 (standard) or 153.2 (ESR), the system is vulnerable.

Impact Analysis

An attacker could exploit this to access sensitive data from one website while you are logged into another site. This could lead to theft of cookies, session tokens, or other private information across different browsing contexts.

Compliance Impact

The provided CVE data does not specify how this vulnerability affects compliance with standards like GDPR or HIPAA. The vulnerability involves a site isolation issue in Firefox's DOM Navigation component, but no direct impact on regulatory compliance is mentioned.

Mitigation Strategies

Update Firefox to version 155 or later and Firefox ESR to version 153.2 or later to address the site isolation issue in the DOM Navigation component.

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