Site Isolation Vulnerability in Firefox Browser by Mozilla
CVE-2026-100821

4.7MEDIUM

Key Information:

Vendor

Mozilla
Status
Firefox
Thunderbird
Vendor
CVE Published:
29 September 2026

What is CVE-2026-100821?

A site isolation vulnerability in the Panning and Zooming component of Mozilla's Firefox browser could potentially allow attackers to bypass security measures and access sensitive data across different sites. This issue was identified and subsequently resolved in Firefox versions 153.4, 157, 115.42, and 140.17. Users are advised to update to the latest versions to ensure complete protection against potential exploitation of this issue.

Affected Version(s)

Firefox 115.42

Firefox 140.17

Firefox 153.4

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2071784
https://www.mozilla.org/security/advisories/mfsa2026-100/
https://www.mozilla.org/security/advisories/mfsa2026-101/

CVSS V3.1

Score:
4.7
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
None
Availability:
Low
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
Required
Scope:
Changed

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Nguyen Thanh Nguyen
.