CVE Catalog

CVE-2026-99258

Unknown
Published: Translated: NVD NIST

Summary

In the Linux kernel, hv_apicid_to_vp_index() uses per-CPU hypercall input and output pages. In an SEV-SNP CoCo VM without a paravisor the output page is not allocated, so the hypervisor stores the resulting VP index into memory not allocated by the guest. The fix uses the input page for both input and output.

Risk Assessment

In SEV-SNP CoCo environments this can cause writes outside allocated memory, risking instability or potential compromise of VM isolation. The issue affects Hyper-V configurations with confidential VMs.

Recommendation

Update the Linux kernel to a version containing the hv_apicid_to_vp_index() fix. Higher priority for organizations using SEV-SNP CoCo on Hyper-V.

Other vulnerabilities in Linux kernel

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Original NVD description (English source)

In the Linux kernel, the following vulnerability has been resolved: x86/hyperv: Avoid using per-cpu output page in hv_apicid_to_vp_index() hv_apicid_to_vp_index() currently uses the per-cpu hypercall input and output pages. This function is called when running in VTL2 and when running in an SEV-SNP CoCo VM with no paravisor. In the former case, the output page is allocated, but in the latter case it is not, so the hypervisor stores the output VP index in memory that has not been allocated by the guest. Fix this by using the input page for both input and output. The hypercall has very small input and output, so sharing the same page for both is straightforward. An alternative fix is to allocate the per-cpu output page when running in an SEV-SNP CoCo guest, but this uses significantly more memory, particularly with larger vCPUs counts.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS