CVE-2026-74986

Analyzed Analyzed - Analysis Complete

Firefox 154 CSS Parsing Component Site Isolation Issue

Publication date: 2026-08-18

Last updated on: 2026-08-25

Assigner: Mozilla Corporation

Description

Site isolation issue in the CSS Parsing and Computation component. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-08-18

Last Modified

2026-08-25

Generated

2026-09-07

AI Q&A

2026-08-18

EPSS Evaluated

2026-09-06

NVD

CVE-2026-74986

EUVD

EUVD-2026-60698

Affected Vendors & Products

Vendor	Product	Version / Range
mozilla	firefox	to 153.1.0 (exc)
mozilla	thunderbird	to 153.1.0 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-200	The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.

Attack-Flow Graph

Executive Summary

This is a site isolation issue in the CSS Parsing and Computation component of Firefox. It allows potential cross-site data leaks due to improper separation of content from different sites during CSS processing.

Detection Guidance

This vulnerability is specific to Firefox versions before 154, Firefox ESR before 153.1, Thunderbird before 154, and Thunderbird before 153.1. Detection involves checking installed versions of these applications.

Impact Analysis

An attacker could exploit this to access sensitive data from other websites you visit, such as login credentials or personal information, if you use a vulnerable version of Firefox.

Compliance Impact

This vulnerability could lead to unauthorized data exposure, potentially violating GDPR's data protection requirements or HIPAA's safeguards for protected health information if exploited.

Mitigation Strategies

Update Firefox to version 154 or later and Firefox ESR to version 153.1 or later to address the CSS Parsing and Computation component vulnerability.

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