CVE-2026-124859 is a critical sandbox escape vulnerability in the Storage: Cache API component of Firefox. It arises from incorrect boundary conditions that allow an attacker to break out of the sandbox environment. This flaw was fixed in Firefox 160 and Firefox ESR versions 115.45 and 153.7. The vulnerability has a high CVSS score of 9.6, indicating severe impact on confidentiality, integrity, and availability. No known exploits in the wild have been reported at this time.