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Fencer Vulns
high 8.8

CVE-2021-3656 json

A flaw was found in the KVM's AMD code for supporting SVM nested virtualization.

published 2022-03-04 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-26951

cvss
8.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.7%
EPSS 0.7% chance of exploitation in 30 days, percentile 51%
public exploits
0
none known

Summary

A flaw was found in the KVM's AMD code for supporting SVM nested virtualization. The flaw occurs when processing the VMCB (virtual machine control block) provided by the L1 guest to spawn/handle a nested guest (L2). Due to improper validation of the "virt_ext" field, this issue could allow a malicious L1 to disable both VMLOAD/VMSAVE intercepts and VLS (Virtual VMLOAD/VMSAVE) for the L2 guest. As a result, the L2 guest would be allowed to read/write physical pages of the host, resulting in a crash of the entire system, leak of sensitive data or potential guest-to-host escape.

Patch / fix

  • linux linux_kernel 4.14.245, 4.19.205, 5.4.142, 5.10.60, 5.13.12
  • linux Debian 14, Debian 13, Debian 12 5.14.6-1

debian advisories DEBIAN-CVE-2021-3656

  • linux Ubuntu 18.04 LTS 4.15.0-156.163
  • linux Ubuntu 20.04 LTS 5.4.0-84.94
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1111.118
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1056.59
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1052.56
  • linux-gke Ubuntu 20.04 LTS 5.4.0-1052.55
  • linux-kvm Ubuntu 18.04 LTS 4.15.0-1099.101
  • linux-kvm Ubuntu 20.04 LTS 5.4.0-1046.48

ubuntu advisories UBUNTU-CVE-2021-3656

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

  • kernel RHEL 7 3.10.0-1160.45.1.el7
  • perf RHEL 7 3.10.0-1160.45.1.el7
  • bpftool RHEL 7 3.10.0-1160.45.1.el7
  • python-perf RHEL 7 3.10.0-1160.45.1.el7
  • kernel-kdump RHEL 7 3.10.0-1160.45.1.el7
  • kernel-tools RHEL 7 3.10.0-1160.45.1.el7
  • kernel-tools-libs RHEL 7 3.10.0-1160.45.1.el7
  • kernel-bootwrapper RHEL 7 3.10.0-1160.45.1.el7

red hat advisories RHSA-2021:3801RHSA-2021:3987RHSA-2021:3812RHSA-2021:4056RHSA-2021:4088RHSA-2021:3802

  • kernel-syms SLES for SAP 12 SP4, SLES 12 SP4-LTSS, OpenStack Cloud Crowbar 9 +1 more 4.12.14-95.83.2
  • kernel-source SLES for SAP 12 SP4, SLES 12 SP4-LTSS, OpenStack Cloud Crowbar 9 +1 more 4.12.14-95.83.2
  • kernel-default SLES for SAP 12 SP4, SLES 12 SP4-LTSS, SLE Live Patching 12 SP4 +3 more 4.12.14-95.83.2
  • kernel-syms SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 4.12.14-150.78.1
  • kernel-source SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 4.12.14-150.78.1
  • kernel-default SLES for SAP 15, SLES 15-LTSS, SLE Live Patching 15 +3 more 4.12.14-150.78.1
  • kernel-vanilla SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 4.12.14-150.78.1
  • kernel-obs-build SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 4.12.14-150.78.2

suse advisories SUSE-SU-2021:3972-1SUSE-SU-2021:3969-1SUSE-SU-2021:3876-1SUSE-SU-2021:3415-1SUSE-SU-2021:3205-2SUSE-SU-2021:3217-1

  • kernel-source openSUSE Tumbleweed 5.14.6-1.4
  • kernel-source openSUSE Tumbleweed 6.6.17-1.1
  • kernel-default openSUSE Leap 15.3 4.12.14-197.102.2
  • kernel-vanilla openSUSE Leap 15.3 4.12.14-197.102.2
  • kernel-kvmsmall openSUSE Leap 15.3 4.12.14-197.102.2
  • kernel-zfcpdump openSUSE Leap 15.3 4.12.14-197.102.2
  • dtb-aarch64 openSUSE Leap 15.3 5.3.18-59.24.1
  • kernel-64kb openSUSE Leap 15.3 5.3.18-59.24.1

opensuse advisories openSUSE-SU-2024:10728-1openSUSE-SU-2024:13704-1openSUSE-SU-2021:3876-1openSUSE-SU-2021:3205-1openSUSE-SU-2021:3179-1openSUSE-SU-2021:1271-1

  • kernel-rt Rocky Linux 8 4.18.0-305.25.1.rt7.97.el8_4
  • kernel Rocky Linux 8 4.18.0-305.25.1.el8_4

rocky linux advisories RLSA-2021:4088RLSA-2021:4056

  • linux-hardened Arch Linux 5.13.13.hardened1-1
  • linux Arch Linux 5.13.12.arch1-1
  • linux-zen Arch Linux 5.13.12.zen1-1
  • linux-lts Arch Linux 5.10.60-1

arch linux advisories AVG-2234AVG-2295AVG-2296AVG-2297

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-2021-3656 updated cvss 8.8

kernel: SVM nested virtualization issue in KVM (VMLOAD/VMSAVE)

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat CodeReady Linux Builder (v. 8) kernel-debuginfo-common-x86_64 4.18.0-305.25.1.el8_4, kernel-debuginfo-common-aarch64 4.18.0-305.25.1.el8_4, kernel-debuginfo-common-ppc64le 4.18.0-305.25.1.el8_4
    fixed: vendor fix RHSA-2021:4056
  • Red Hat CodeReady Linux Builder EUS (v. 8.1) kernel-debuginfo-common-x86_64 4.18.0-147.56.1.el8_1, kernel-debuginfo-common-aarch64 4.18.0-147.56.1.el8_1, kernel-debuginfo-common-ppc64le 4.18.0-147.56.1.el8_1
    fixed: vendor fix RHSA-2021:3676
  • Red Hat CodeReady Linux Builder EUS (v. 8.2) kernel-debuginfo-common-x86_64 4.18.0-193.68.1.el8_2, kernel-debuginfo-common-aarch64 4.18.0-193.68.1.el8_2, kernel-debuginfo-common-ppc64le 4.18.0-193.68.1.el8_2
    fixed: vendor fix RHSA-2021:3904
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-305.25.1.el8_4, kernel 4.18.0-305.25.1.el8_4, bpftool 4.18.0-305.25.1.el8_4, kernel-core 4.18.0-305.25.1.el8_4, kernel-tools 4.18.0-305.25.1.el8_4, python3-perf 4.18.0-305.25.1.el8_4, +15 more
    fixed: vendor fix RHSA-2021:4056
  • Red Hat Enterprise Linux BaseOS EUS (v. 8.1) perf 4.18.0-147.56.1.el8_1, kernel 4.18.0-147.56.1.el8_1, bpftool 4.18.0-147.56.1.el8_1, kernel-core 4.18.0-147.56.1.el8_1, kernel-tools 4.18.0-147.56.1.el8_1, python3-perf 4.18.0-147.56.1.el8_1, +15 more
    fixed: vendor fix RHSA-2021:3676
  • Red Hat Enterprise Linux BaseOS EUS (v. 8.2) perf 4.18.0-193.68.1.el8_2, kernel 4.18.0-193.68.1.el8_2, bpftool 4.18.0-193.68.1.el8_2, kernel-core 4.18.0-193.68.1.el8_2, kernel-tools 4.18.0-193.68.1.el8_2, python3-perf 4.18.0-193.68.1.el8_2, +15 more
    fixed: vendor fix RHSA-2021:3904
  • Red Hat Enterprise Linux Client (v. 7) perf 3.10.0-1160.45.1.el7, kernel 3.10.0-1160.45.1.el7, bpftool 3.10.0-1160.45.1.el7, python-perf 3.10.0-1160.45.1.el7, kernel-tools 3.10.0-1160.45.1.el7, kernel-tools-libs 3.10.0-1160.45.1.el7, +2 more Red Hat Enterprise Linux Client Optional (v. 7) kernel-debuginfo-common-x86_64 3.10.0-1160.45.1.el7 Red Hat Enterprise Linux ComputeNode Optional (v. 7) kernel-debuginfo-common-x86_64 3.10.0-1160.45.1.el7
    fixed: vendor fix RHSA-2021:3801
show 21 more
  • Red Hat Enterprise Linux for Real Time (v. 7) kernel-rt 3.10.0-1160.45.1.rt56.1185.el7, kernel-rt-trace 3.10.0-1160.45.1.rt56.1185.el7, kernel-rt-debuginfo-common-x86_64 3.10.0-1160.45.1.rt56.1185.el7 Red Hat Enterprise Linux for Real Time for NFV (v. 7) kernel-rt 3.10.0-1160.45.1.rt56.1185.el7, kernel-rt-kvm 3.10.0-1160.45.1.rt56.1185.el7, kernel-rt-trace 3.10.0-1160.45.1.rt56.1185.el7, kernel-rt-debug-kvm 3.10.0-1160.45.1.rt56.1185.el7, kernel-rt-trace-kvm 3.10.0-1160.45.1.rt56.1185.el7, kernel-rt-debuginfo-common-x86_64 3.10.0-1160.45.1.rt56.1185.el7
    fixed: vendor fix RHSA-2021:3802
  • Red Hat Enterprise Linux Real Time (v. 8) kernel-rt 4.18.0-305.25.1.rt7.97.el8_4, kernel-rt-core 4.18.0-305.25.1.rt7.97.el8_4, kernel-rt-modules 4.18.0-305.25.1.rt7.97.el8_4, kernel-rt-debug-core 4.18.0-305.25.1.rt7.97.el8_4, kernel-rt-debug-modules 4.18.0-305.25.1.rt7.97.el8_4, kernel-rt-modules-extra 4.18.0-305.25.1.rt7.97.el8_4, +2 more
    fixed: vendor fix RHSA-2021:4088
  • Red Hat Enterprise Linux Real Time EUS (v. 8.2) kernel-rt 4.18.0-193.68.1.rt13.118.el8_2, kernel-rt-core 4.18.0-193.68.1.rt13.118.el8_2, kernel-rt-modules 4.18.0-193.68.1.rt13.118.el8_2, kernel-rt-debug-core 4.18.0-193.68.1.rt13.118.el8_2, kernel-rt-debug-modules 4.18.0-193.68.1.rt13.118.el8_2, kernel-rt-modules-extra 4.18.0-193.68.1.rt13.118.el8_2, +2 more
    fixed: vendor fix RHSA-2021:3909
  • Red Hat Enterprise Linux Real Time for NFV (v. 8) kernel-rt 4.18.0-305.25.1.rt7.97.el8_4, kernel-rt-kvm 4.18.0-305.25.1.rt7.97.el8_4, kernel-rt-core 4.18.0-305.25.1.rt7.97.el8_4, kernel-rt-modules 4.18.0-305.25.1.rt7.97.el8_4, kernel-rt-debug-kvm 4.18.0-305.25.1.rt7.97.el8_4, kernel-rt-debug-core 4.18.0-305.25.1.rt7.97.el8_4, +4 more
    fixed: vendor fix RHSA-2021:4088
  • Red Hat Enterprise Linux Real Time for NFV EUS (v. 8.2) kernel-rt 4.18.0-193.68.1.rt13.118.el8_2, kernel-rt-kvm 4.18.0-193.68.1.rt13.118.el8_2, kernel-rt-core 4.18.0-193.68.1.rt13.118.el8_2, kernel-rt-modules 4.18.0-193.68.1.rt13.118.el8_2, kernel-rt-debug-kvm 4.18.0-193.68.1.rt13.118.el8_2, kernel-rt-debug-core 4.18.0-193.68.1.rt13.118.el8_2, +4 more
    fixed: vendor fix RHSA-2021:3909
  • Red Hat Enterprise Linux Server (v. 7) perf 3.10.0-1160.45.1.el7, kernel 3.10.0-1160.45.1.el7, bpftool 3.10.0-1160.45.1.el7, python-perf 3.10.0-1160.45.1.el7, kernel-kdump 3.10.0-1160.45.1.el7, kernel-tools 3.10.0-1160.45.1.el7, +7 more
    fixed: vendor fix RHSA-2021:3801
  • Red Hat Enterprise Linux Server AUS (v. 7.6) perf 3.10.0-957.84.1.el7, kernel 3.10.0-957.84.1.el7, bpftool 3.10.0-957.84.1.el7, python-perf 3.10.0-957.84.1.el7, kernel-tools 3.10.0-957.84.1.el7, kernel-tools-libs 3.10.0-957.84.1.el7, +2 more
    fixed: vendor fix RHSA-2021:3812
  • Red Hat Enterprise Linux Server AUS (v. 7.7) perf 3.10.0-1062.59.1.el7, kernel 3.10.0-1062.59.1.el7, bpftool 3.10.0-1062.59.1.el7, python-perf 3.10.0-1062.59.1.el7, kernel-tools 3.10.0-1062.59.1.el7, kernel-tools-libs 3.10.0-1062.59.1.el7, +2 more
    fixed: vendor fix RHSA-2021:3987
  • Red Hat Enterprise Linux Server E4S (v. 7.6) perf 3.10.0-957.84.1.el7, kernel 3.10.0-957.84.1.el7, python-perf 3.10.0-957.84.1.el7, kernel-tools 3.10.0-957.84.1.el7, kernel-tools-libs 3.10.0-957.84.1.el7, kernel-bootwrapper 3.10.0-957.84.1.el7, +3 more
    fixed: vendor fix RHSA-2021:3812
  • Red Hat Enterprise Linux Server E4S (v. 7.7) perf 3.10.0-1062.59.1.el7, kernel 3.10.0-1062.59.1.el7, bpftool 3.10.0-1062.59.1.el7, python-perf 3.10.0-1062.59.1.el7, kernel-tools 3.10.0-1062.59.1.el7, kernel-tools-libs 3.10.0-1062.59.1.el7, +4 more
    fixed: vendor fix RHSA-2021:3987
  • Red Hat Enterprise Linux Server Optional (v. 7) kernel-debuginfo-common-ppc64 3.10.0-1160.45.1.el7, kernel-debuginfo-common-x86_64 3.10.0-1160.45.1.el7, kernel-debuginfo-common-ppc64le 3.10.0-1160.45.1.el7
    fixed: vendor fix RHSA-2021:3801
  • Red Hat Enterprise Linux Server Optional AUS (v. 7.6) kernel-debuginfo-common-x86_64 3.10.0-957.84.1.el7
    fixed: vendor fix RHSA-2021:3812
  • Red Hat Enterprise Linux Server Optional AUS (v. 7.7) kernel-debuginfo-common-x86_64 3.10.0-1062.59.1.el7
    fixed: vendor fix RHSA-2021:3987
  • Red Hat Enterprise Linux Server Optional E4S (v. 7.6) kernel-debuginfo-common-x86_64 3.10.0-957.84.1.el7, kernel-debuginfo-common-ppc64le 3.10.0-957.84.1.el7
    fixed: vendor fix RHSA-2021:3812
  • Red Hat Enterprise Linux Server Optional E4S (v. 7.7) kernel-debuginfo-common-x86_64 3.10.0-1062.59.1.el7, kernel-debuginfo-common-ppc64le 3.10.0-1062.59.1.el7
    fixed: vendor fix RHSA-2021:3987
  • Red Hat Enterprise Linux Server Optional TUS (v. 7.6) kernel-debuginfo-common-x86_64 3.10.0-957.84.1.el7
    fixed: vendor fix RHSA-2021:3812
  • Red Hat Enterprise Linux Server Optional TUS (v. 7.7) kernel-debuginfo-common-x86_64 3.10.0-1062.59.1.el7
    fixed: vendor fix RHSA-2021:3987
  • Red Hat Enterprise Linux Server TUS (v. 7.6) perf 3.10.0-957.84.1.el7, kernel 3.10.0-957.84.1.el7, bpftool 3.10.0-957.84.1.el7, python-perf 3.10.0-957.84.1.el7, kernel-tools 3.10.0-957.84.1.el7, kernel-tools-libs 3.10.0-957.84.1.el7, +2 more
    fixed: vendor fix RHSA-2021:3812
  • Red Hat Enterprise Linux Server TUS (v. 7.7) perf 3.10.0-1062.59.1.el7, kernel 3.10.0-1062.59.1.el7, bpftool 3.10.0-1062.59.1.el7, python-perf 3.10.0-1062.59.1.el7, kernel-tools 3.10.0-1062.59.1.el7, kernel-tools-libs 3.10.0-1062.59.1.el7, +2 more
    fixed: vendor fix RHSA-2021:3987
  • Red Hat Enterprise Linux Workstation (v. 7) perf 3.10.0-1160.45.1.el7, kernel 3.10.0-1160.45.1.el7, bpftool 3.10.0-1160.45.1.el7, python-perf 3.10.0-1160.45.1.el7, kernel-tools 3.10.0-1160.45.1.el7, kernel-tools-libs 3.10.0-1160.45.1.el7, +2 more Red Hat Enterprise Linux Workstation Optional (v. 7) kernel-debuginfo-common-x86_64 3.10.0-1160.45.1.el7
    fixed: vendor fix RHSA-2021:3801
  • Red Hat Enterprise Linux 7 perf, kernel, kernel-alt, python-perf, kernel-kdump, kernel-tools, +3 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +82 more Red Hat Enterprise Linux BaseOS EUS (v. 8.2) kernel-headers 4.18.0-193.68.1.el8_2
    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

0.66% chance of exploitation in the next 30 days, higher than 51% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 8.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
NVD 2.0 7.2 AV:L/AC:L/Au:N/C:C/I:C/A:C

Affected products

  • n/a KVM

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns 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.