CVE-2026-53361 AF_Unix GC vs. MSG_PEEK use-after-free container escape

A use-after-free vulnerability (CVE-2026-53361) exists in the Linux kernel's AF_UNIX socket garbage collector that allows unprivileged users to escape containers by exploiting a race condition between garbage collection and MSG_PEEK operations. The bug occurs because the garbage collector's gc_in_progress flag can read as false mid-collection, allowing a concurrent MSG_PEEK to take a reference that the collector doesn't account for, resulting in a freed socket still being in use. Multiple kernel versions including Linux 6.12 and Ubuntu 24.04 are vulnerable, with patches available in recent kernel updates.