CVE-2026-12457 is a security vulnerability in Google Chrome's Extensions implementation before version 149.0.7827.155. It involves insufficient data validation that enables a remote attacker, with control over the renderer process, to bypass site isolation protections via a specially crafted HTML page. Site isolation is a key security feature designed to prevent malicious web content from accessing data in other sites' processes. The vulnerability was publicly disclosed on June 17, 2026. No official remediation level or patch details are explicitly stated in the available vendor advisory, though the affected versions include all versions before 149.0.7827.155.

If exploited, this vulnerability could allow an attacker who has already compromised the renderer process to bypass Chrome's site isolation feature, potentially leading to unauthorized access to data across different site processes. This undermines a critical security boundary in the browser, increasing the risk of data leakage or further compromise. However, there are no known exploits in the wild at the time of disclosure.

The vendor advisory linked does not explicitly state the availability of a patch or remediation level. The affected versions include all Chrome versions prior to 149.0.7827.155. Users and administrators should update to version 149.0.7827.155 or later once available to mitigate this vulnerability. Patch status is not yet confirmed—check the vendor advisory for current remediation guidance.