CVE-2026-74962 is a site isolation issue affecting the Networking: Cookies component in Mozilla Firefox. Site isolation is a security mechanism designed to separate web content from different origins into different processes to prevent data leaks and cross-site attacks. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1 as part of a comprehensive security update addressing multiple vulnerabilities. The Mozilla advisories confirm the fix and categorize the impact of this issue as moderate. No known exploits in the wild have been reported.

The vulnerability could potentially allow a site isolation bypass related to cookie handling in the Networking component, which may lead to unauthorized access to cookie data or cross-origin information leakage. However, the impact is assessed as moderate by Mozilla. There is no indication of active exploitation in the wild. The fix eliminates the risk by correcting the site isolation enforcement.

Mozilla has released official fixes for this vulnerability in Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1. Users and administrators should update to these versions or later to remediate the issue. Since this is not a cloud service, patching the client software is required. No additional mitigation steps are indicated by the vendor advisory.