CVE-2026-100821

Undergoing Analysis Undergoing Analysis - In Progress

Firefox Site Isolation Flaw in Panning and Zooming Component

Publication date: 2026-09-29

Last updated on: 2026-10-13

Assigner: Mozilla Corporation

Description

Site isolation issue in the Panning and Zooming component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-09-29

Last Modified

2026-10-13

Generated

2026-10-19

AI Q&A

2026-09-29

EPSS Evaluated

2026-10-18

NVD

CVE-2026-100821

EUVD

EUVD-2026-88800

Affected Vendors & Products

Vendor	Product	Version / Range
mozilla	firefox	From 154.0.0 (inc) to 157.0.0 (exc)
mozilla	thunderbird	From 154.0 (inc) to 157.0 (exc)
mozilla	firefox	to 115.42.0 (exc)
mozilla	thunderbird	to 140.17.0 (exc)
mozilla	thunderbird	From 141.0 (inc) to 153.4.0 (exc)
mozilla	firefox	From 116.0.0 (inc) to 140.17.0 (exc)
mozilla	firefox	From 141.0.0 (inc) to 153.4.0 (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 the Panning and Zooming component of Firefox. 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 between sites.

Detection Guidance

Detection requires checking Firefox version against patched releases. Compare installed version with Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, or Firefox ESR 140.17. Use commands like 'firefox --version' or check 'about:support' in Firefox.

Impact Analysis

An attacker could exploit this to access sensitive data from other websites you have open, such as cookies, session tokens, or personal information. This could lead to account hijacking, data theft, or unauthorized actions on your behalf.

Compliance Impact

The provided CVE data does not specify how this vulnerability impacts compliance with standards like GDPR or HIPAA. The description only mentions a site isolation issue in the Panning and Zooming component without details on data exposure or regulatory implications.

Mitigation Strategies

Update Firefox to the latest patched version immediately. For ESR users, upgrade to Firefox ESR 153.4 or 115.42. For standard releases, upgrade to Firefox 157 or ESR 140.17. Disable unnecessary extensions if updates are delayed.

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