CVE-2026-84140

Modified Modified - Updated After Analysis

DOM Navigation Site Isolation Bypass in Firefox

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:
Percentile:

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-2026-84140

EUVD

EUVD-2026-69088

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 vulnerability is a site isolation issue in the DOM Navigation component of Firefox. It was patched in Firefox 155 and Firefox ESR 153.2. Site isolation is a security feature that separates different websites to prevent malicious sites from accessing data from other sites.

Detection Guidance

This vulnerability is specific to Firefox versions before 155 and Firefox ESR before 153.2. Detection involves checking installed Firefox versions. On Linux, run 'firefox --version' or 'dpkg -l firefox' (Debian/Ubuntu) or 'rpm -qa firefox' (RHEL/Fedora). On Windows, check 'Programs and Features' or run 'where firefox' in Command Prompt. If versions are below 155 or 153.2 respectively, the system is vulnerable.

Impact Analysis

An attacker could exploit this to access sensitive data from other sites you visit, such as login credentials or personal information. This could lead to identity theft, financial loss, or unauthorized access to accounts.

Compliance Impact

The provided CVE data does not specify how this vulnerability impacts compliance with standards like GDPR or HIPAA. The description focuses on a site isolation issue in Firefox's DOM Navigation component, fixed in versions 155 and ESR 153.2, but lacks details on regulatory implications.

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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