A flaw in Linux kernel’s sched/mmcid code causes an infinite loop when a vfork()‑ed task is scheduled. The logic that counts vfork() tasks mistakenly stops the walk when the counted tasks exceed the number of MMCID users, leaving the task’s CID unassigned. Once this occurs, subsequent scheduling attempts cannot acquire a transitional CID and the kernel stalls, resulting in a system freeze and loss of service availability.

The vulnerability affects all Linux kernel releases that include the buggy sched/mmcid implementation and have not yet incorporated the patch found in the linked commits. No specific version numbers are provided, so any current kernel variant lacking these changes could be vulnerable. The impact is limited to Linux systems, irrespective of distribution, as it resides in the core kernel.

The CVSS score is not reported and EPSS is unavailable, but the impact of a kernel stall is consequential. Exploitation would likely require local privileged execution, such as creating a vfork()’ed process with a multithreaded parent. The absence of a KEV listing implies no publicly known exploits, yet the bug’s potential to halt critical services makes it a compelling target for attackers. Until the kernel is patched or upgraded, the risk remains high.