CVE-2026-100816

Analyzed Analyzed - Analysis Complete

Firefox Site Isolation DOM Networking Component Bypass

Publication date: 2026-09-29

Last updated on: 2026-10-05

Assigner: Mozilla Corporation

Description

Site isolation issue in the DOM: Networking component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 153.4, and Firefox 157.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-09-29

Last Modified

2026-10-05

Generated

2026-10-19

AI Q&A

2026-09-29

EPSS Evaluated

2026-10-18

NVD

CVE-2026-100816

EUVD

EUVD-2026-88795

Affected Vendors & Products

Vendor	Product	Version / Range
mozilla	firefox	to 153.4.0 (exc)
mozilla	firefox	From 154.0.0 (inc) to 157.0.0 (exc)
mozilla	thunderbird	to 153.4.0 (exc)
mozilla	thunderbird	From 154.0 (inc) to 157.0 (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 and Networking components. It allows potential data leakage between different websites due to improper separation of site contexts. The vulnerability was patched in Firefox ESR 153.4 and Firefox 157.

Detection Guidance

This vulnerability is specific to Firefox and Thunderbird versions before 157 (ESR 153.4). Detection involves checking installed versions of these applications. For Firefox, run 'firefox --version' or check 'about:support' in the browser. For Thunderbird, run 'thunderbird --version'. If versions are below 157 or 153.4 (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. This might include cookies, session tokens, or other private information, potentially leading to account hijacking or data theft.

Compliance Impact

This vulnerability could lead to unauthorized data exposure, violating GDPR's data protection principles or HIPAA's confidentiality requirements. Organizations using affected Firefox versions may face compliance violations and potential fines if user data is compromised.

Mitigation Strategies

Update Firefox ESR to version 153.4 or Firefox to version 157 or later to address the site isolation issue in the DOM: Networking component.

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