Copyright © 2012 Red Hat, Inc. All rights reserved. Moderate 2026-11-03T11:25:14 kernel: kernel: hyperv: Memory corruption via unallocated hypercall output page 4.1 CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H CWE-787

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.

A flaw was found in the Linux kernel's Hyper-V subsystem. When operating in an AMD Secure Encrypted Virtualization-Secure Nested Paging (SEV-SNP) confidential virtual machine without a paravisor, the kernel fails to allocate an output buffer for hypervisor communication. Consequently, querying virtual processor information causes the hypervisor to write into unallocated guest memory, which can lead to memory corruption, system instability, or a Denial of Service (DoS).

Red Hat Enterprise Linux 10 Fix deferred kernel Red Hat Enterprise Linux 6 Not affected kernel Red Hat Enterprise Linux 7 Not affected kernel Red Hat Enterprise Linux 7 Not affected kernel-rt Red Hat Enterprise Linux 8 Not affected kernel Red Hat Enterprise Linux 8 Not affected kernel-rt Red Hat Enterprise Linux 9 Fix deferred kernel Red Hat Enterprise Linux 9 Not affected kernel-rt Red Hat OpenShift Container Platform 4 Not affected openshift/ose-rhel-coreos-8 Red Hat OpenShift Container Platform 4 Fix deferred openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 Fix deferred openshift/ose-rhel-coreos-10 Red Hat OpenShift Container Platform 5 Fix deferred openshift/ose-rhel-coreos-9 https://www.cve.org/CVERecord?id=CVE-2026-99258 https://nvd.nist.gov/vuln/detail/CVE-2026-99258 https://git.kernel.org/stable/c/2b561786c9076a892ef8b8f416c9828bc87ed44f https://git.kernel.org/stable/c/7b74c117e2aac78e0f723e1c9c3644451c56b0d9 https://git.kernel.org/stable/c/bc8ca0f4769627ae7d04e7ffdbd20de4f27a9bf9 https://git.kernel.org/stable/c/bdba5f1b8bd0d18b1df61f769b559ed272902489