CVE-2026-74962

Undergoing Analysis Undergoing Analysis - In Progress

Site Isolation Bypass in Firefox via Cookies Component

Publication date: 2026-08-18

Last updated on: 2026-08-19

Assigner: Mozilla Corporation

Description

Site isolation issue in the Networking: Cookies component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-08-18

Last Modified

2026-08-19

Generated

2026-09-08

AI Q&A

2026-08-18

EPSS Evaluated

2026-09-07

NVD

CVE-2026-74962

EUVD

EUVD-2026-60660

Affected Vendors & Products

Vendor	Product	Version / Range
mozilla	thunderbird	From 141.0 (inc) to 153.1.0 (exc)
mozilla	thunderbird	to 140.14.0 (exc)
mozilla	firefox	to 140.14.0 (exc)
mozilla	firefox	From 141.0.0 (inc) to 153.1.0 (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 Networking: Cookies component. Site isolation is a security feature that separates content from different websites to prevent malicious sites from accessing data from other sites. A flaw in this component could allow unauthorized access or manipulation of cookies across different sites.

Detection Guidance

This vulnerability is specific to Firefox versions before 154, Firefox ESR 140.14, and Firefox ESR 153.1. Detection involves checking installed Firefox versions. Use commands like 'firefox --version' or check package managers (e.g., 'apt list --installed | grep firefox' for Debian/Ubuntu). If versions are below the fixed releases, the system is vulnerable.

Impact Analysis

If exploited, this vulnerability could allow an attacker to steal or manipulate cookies from other websites, potentially leading to session hijacking, unauthorized account access, or exposure of sensitive data stored in cookies.

Compliance Impact

This vulnerability could lead to unauthorized access to personal data, which may violate GDPR's data protection requirements or HIPAA's safeguards for protected health information. Organizations using affected Firefox versions may face compliance risks if exploited.

Mitigation Strategies

Update Firefox to version 154 or later, Firefox ESR 140.14 or later, or Firefox ESR 153.1 or later to address the site isolation issue in the Networking: Cookies component.

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