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no cvss —

CVE-2026-99258 json

x86/hyperv: Avoid using per-cpu output page in hv_apicid_to_vp_index()

published 6d ago modified 6d ago also EUVD-2026-115769

cvss
—
not scored
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 8%
public exploits
0
none known

Summary

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.

Patch / fix

  • Linux Linux 6.12.115, 6.16, 6.18.59, 7.2.13, 7.3
  • linux Debian 13 6.12.115-1
  • linux Debian 14 7.2.13-1

debian advisories DEBIAN-CVE-2026-99258

  • linux Ubuntu 26.10 7.3.0-10.10
  • linux-aws Ubuntu 26.10 7.3.0-1004.4
  • linux-gcp Ubuntu 26.10 7.3.0-1004.4
  • linux-raspi Ubuntu 26.10 7.3.0-1004.4
  • linux-riscv Ubuntu 26.10 7.3.0-10.10.1
  • linux-oracle Ubuntu 26.10 7.3.0-1004.4
  • linux-realtime Ubuntu 26.10 7.3.0-10.10.1

ubuntu advisories UBUNTU-CVE-2026-99258

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-99258 updated cvss 4.1

kernel: kernel: hyperv: Memory corruption via unallocated hypercall output page

  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +82 more Red Hat Enterprise Linux 10 kernel Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9, openshift/ose-rhel-coreos-10
    affected: no fix available “Fix deferred”
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-selftests-internal Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.19% chance of exploitation in the next 30 days, higher than 8% of all scored CVEs (FIRST EPSS, 2026-11-09).

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.