CVE-2026-74960
Undergoing Analysis Undergoing Analysis - In Progress

Site Isolation Bypass in Firefox WebExtensions

Publication date: 2026-08-18

Last updated on: 2026-08-18

Assigner: Mozilla Corporation

Description
Site isolation issue in the WebExtensions component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1.

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Meta Information

Published
2026-08-18
Last Modified
2026-08-18
Generated
2026-08-18
AI Q&A
2026-08-18
EPSS Evaluated
N/A
NVD
CVE-2026-74960
EUVD
EUVD-2026-60659

Affected Vendors & Products

Showing 8 associated CPEs
Vendor Product Version / Range
mozilla firefox to 154 (inc)
mozilla firefox to 140.14 (inc)
mozilla firefox to 153.1 (inc)
mozilla firefox_esr to 140.14 (inc)
mozilla firefox_esr to 153.1 (inc)
mozilla firefox 154
mozilla firefox_esr 140.14
mozilla firefox_esr 153.1

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a site isolation issue in Firefox's WebExtensions component. Site isolation is a security feature that separates content from different sites to prevent malicious websites from accessing data from other sites. A flaw in this feature could allow an attacker to bypass these protections and access sensitive information across different sites.

Detection Guidance

Detection requires checking Firefox version against patched releases. Compare installed version with Firefox 154, Firefox ESR 140.14, or Firefox ESR 153.1. Use commands like 'firefox --version' or check 'about:support' in Firefox.

Impact Analysis

If exploited, this vulnerability could allow an attacker to access data from other websites you are logged into, such as cookies, session tokens, or sensitive information. This could lead to account takeovers, data theft, or unauthorized actions on your behalf.

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 immediately. Disable WebExtensions if updates are not possible.

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