A vulnerability in the Linux kernel futex subsystem involving FUT_OFF_MMSHARED futexes has been fixed. The issue allowed processes to wait on shared futexes referencing a freed memory management structure (MM), causing wakeups to be misdirected to new MMs at the same address. This was addressed by using a unique 64-bit per-MM ID to key FUT_OFF_MMSHARED futexes, preventing cross-MM wakeup consumption.