CISA flags CVE-2026-53362 kernel flaw that breaks container isolation assumptions

CISA added CVE-2026-53362, dubbed 'Frag Gap,' to its Known Exploited Vulnerabilities catalog on August 27, 2026, flagging it as actively exploited in the wild. The flaw is an out-of-bounds write in the Linux kernel's IPv6 fragmentation path, carrying a CVSS score of 7.8. Unlike virtual machines, containers share the host's Linux kernel, meaning a kernel-level vulnerability affects all containers and the host simultaneously. An attacker needs only an initial foothold — such as a compromised web app or stolen credentials — and the ability to create a UDP socket to trigger the exploit and corrupt host kernel memory. The vulnerability exposes a widespread misconception that container isolation provides the same security boundary as hypervisor-based virtualization.