CVE-2026-74956 is a vulnerability in Mozilla Firefox's DOM Service Workers component that allows bypassing the same-origin policy. The same-origin policy is a fundamental browser security mechanism that restricts how documents or scripts loaded from one origin can interact with resources from another origin. This vulnerability could potentially allow unauthorized access to resources across origins. Mozilla fixed this issue in Firefox 154 and Firefox ESR 153.1 as part of a broader security update addressing multiple vulnerabilities. The vendor advisory explicitly states the fix and moderate impact level.

The vulnerability enables bypassing the same-origin policy in the Service Workers component, potentially allowing cross-origin access that should be restricted. This could lead to unauthorized information disclosure or other security issues related to origin isolation. However, the vendor rates the impact as moderate and no active exploitation has been reported.

Mozilla has released official fixes for this vulnerability in Firefox 154 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, remediation depends on applying the vendor's patches. No additional mitigation steps are specified or required beyond updating to the fixed versions.