The flaw originates from the removal of the X86_CR4_FRED bit from the CR4 pinned bits mask in the Linux kernel’s x86 CPU code. This change creates a brief period during boot where the FRED MSR is not yet initialized, meaning that if an exception occurs in that window – for example when a SEV‑ES/SNP or TDX guest triggers an exception – the host will experience a triple fault and crash. The impact is a kernel panic that results in a loss of service but does not provide a direct escalation of privileges to an attacker.

All Linux kernel versions that include the broken CR4 pinning logic – specifically the 6.9 series and all 7.0 release candidates up to rc7 – are affected. The issue exists on the default Linux distribution kernels; no user‑space applications are directly impacted.

With a CVSS score of 5.5 the vulnerability is considered of moderate severity. The EPSS score of < 1 % indicates a low likelihood of exploitation in the wild, and the vulnerability is not listed in CISA’s KEV catalog. Exploitation requires privileged kernel access or the ability to run a guest that can trigger an exception during the narrow initialization window, making it less likely to be abused in the real world.