GhostLock (CVE-2026-43499) is a Linux kernel flaw that has existed in all major distributions since 2011. The vulnerability was introduced in Linux kernel version 2.6.39 and was fixed in version 7.1. It requires no special configuration or elevated privileges to exploit. An unprivileged local attacker can trigger a use-after-free condition in the rt_mutex_remove_waiter function by causing a requeue-PI deadlock. The bug allows manipulation of a kernel stack pointer, enabling arbitrary writes and privilege escalation to root, and can be used to escape containers. Researchers demonstrated the issue by leaking the kernel image address with a prefetch timing attack, reclaiming the freed stack frame through the PR_SET_MM_MAP system call, and forging a fake rt_mutex_waiter that overwrites the inet6_protos table to gain control of a kernel function. A subsequent write to the core_pattern sysctl makes the core dump file world‑writable, completing the privilege escalation. The kernel patch updates remove_waiter to lock the task that owns the waiter before clearing its pi_blocked_on field. Distributions are urged to apply the update or upgrade to the latest long‑term support release. The vulnerability was publicly disclosed on July 7, 2026, and a working exploit is available in the open‑source research project.