Linux Kernel Memory CID Out-of-Bounds Clear Bit Flaw

CVE-2026-63799 is a high-severity out-of-bounds (OOB) vulnerability in the Linux kernel's process scheduling subsystem, specifically in the mm_cid (memory context identifier) fixup path. The vulnerability occurs when the kernel attempts to clear a bit for an uninitialized CID value (MM_CID_UNSET) during CPU-to-task fixup operations. This affects systems running vulnerable Linux kernel versions, particularly those using per-CPU mode scheduling where newly forked or exec'd tasks may have uninitialized CIDs. The flaw can lead to memory corruption, kernel crashes, or potential privilege escalation, impacting any organization running affected Linux systems across servers, workstations, and embedded devices.

While Casky.ai currently shows zero matching skills for this specific CVE, practitioners using Casky's 754 security skills mapped to MITRE ATT&CK would typically leverage detection around kernel exploitation patterns, privilege escalation attempts, and system instability indicators. Although direct MITRE ATT&CK technique mapping is unavailable for this CVE, security teams should monitor for techniques such as T1548 (Abuse Elevation Control Mechanism) and T1562 (Impair Defenses) that could result from successful kernel exploitation. Organizations should prioritize kernel patching through their vulnerability management processes and monitor system logs for unexpected kernel panics, memory access violations, or abnormal process behavior that could indicate exploitation attempts.