CVE-2021-3656: High severity linux kernel vulnerability
Published Jul 20, 2021
·Updated
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 "virtext" 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.
Affected Software
101 affected componentsFixes available
redhat/kernel-rt<0:3.10.0-1160.45.1.rt56.1185.el7
0:3.10.0-1160.45.1.rt56.1185.el7
redhat/kernel<0:3.10.0-1160.45.1.el7
0:3.10.0-1160.45.1.el7
redhat/kernel<0:3.10.0-957.84.1.el7
0:3.10.0-957.84.1.el7
redhat/kernel<0:3.10.0-1062.59.1.el7
0:3.10.0-1062.59.1.el7
redhat/kernel-rt<0:4.18.0-305.25.1.rt7.97.el8_4
0:4.18.0-305.25.1.rt7.97.el8_4
redhat/kernel<0:4.18.0-305.25.1.el8_4
0:4.18.0-305.25.1.el8_4
redhat/kernel<0:4.18.0-147.56.1.el8_1
0:4.18.0-147.56.1.el8_1
redhat/kernel-rt<0:4.18.0-193.68.1.rt13.118.el8_2
0:4.18.0-193.68.1.rt13.118.el8_2
redhat/kernel<0:4.18.0-193.68.1.el8_2
0:4.18.0-193.68.1.el8_2
redhat/kernel<5.14
5.14
Linux Linux kernel>=4.13<4.14.245
Linux Linux kernel>=4.15<4.19.205
Linux Linux kernel>=4.20<5.4.142
Linux Linux kernel>=5.5<5.10.60
Linux Linux kernel>=5.11<5.13.12
Linux Linux kernel=5.14
Linux Linux kernel=5.14-rc1
Linux Linux kernel=5.14-rc2
Linux Linux kernel=5.14-rc3
Linux Linux kernel=5.14-rc4
Linux Linux kernel=5.14-rc5
Linux Linux kernel=5.14-rc6
Fedoraproject Fedora=33
Fedoraproject Fedora=34
All of the following
redhat Software Collections
redhat Enterprise Linux Server=7.0
redhat Openstack=13
redhat Enterprise Linux=8.0
redhat Enterprise Linux Desktop=7.0
redhat Enterprise Linux Eus=8.1
redhat Enterprise Linux Eus=8.2
redhat Enterprise Linux Eus=8.4
redhat Enterprise Linux For Ibm Z Systems=7.0
redhat Enterprise Linux For Ibm Z Systems=8.0
redhat Enterprise Linux For Ibm Z Systems Eus=8.1
redhat Enterprise Linux For Ibm Z Systems Eus=8.2
redhat Enterprise Linux For Ibm Z Systems Eus=8.4
redhat Enterprise Linux For Power Big Endian=7.0
redhat Enterprise Linux For Power Little Endian=7.0
redhat Enterprise Linux For Power Little Endian=8.0
redhat Enterprise Linux For Power Little Endian Eus=8.1
redhat Enterprise Linux For Power Little Endian Eus=8.2
redhat Enterprise Linux For Power Little Endian Eus=8.4
redhat Enterprise Linux For Real Time=7
redhat Enterprise Linux For Real Time=8
redhat Enterprise Linux For Real Time For Nfv=7
redhat Enterprise Linux For Real Time For Nfv=8
redhat Enterprise Linux For Real Time For Nfv Tus=8.2
redhat Enterprise Linux For Real Time For Nfv Tus=8.4
redhat Enterprise Linux For Real Time Tus=8.2
redhat Enterprise Linux For Real Time Tus=8.4
redhat Enterprise Linux For Scientific Computing=7.0
redhat Enterprise Linux Server=7.0
redhat Enterprise Linux Server Aus=7.6
redhat Enterprise Linux Server Aus=7.7
redhat Enterprise Linux Server Aus=8.2
redhat Enterprise Linux Server Aus=8.4
redhat Enterprise Linux Server For Power Little Endian Update Services For Sap Solutions=7.6
redhat Enterprise Linux Server For Power Little Endian Update Services For Sap Solutions=8.1
redhat Enterprise Linux Server For Power Little Endian Update Services For Sap Solutions=8.2
redhat Enterprise Linux Server For Power Little Endian Update Services For Sap Solutions=8.4
redhat Enterprise Linux Server Tus=7.6
redhat Enterprise Linux Server Tus=7.7
redhat Enterprise Linux Server Tus=8.2
redhat Enterprise Linux Server Tus=8.4
redhat Enterprise Linux Server Update Services For Sap Solutions=7.6
redhat Enterprise Linux Server Update Services For Sap Solutions=7.7
redhat Enterprise Linux Server Update Services For Sap Solutions=8.1
redhat Enterprise Linux Server Update Services For Sap Solutions=8.2
redhat Enterprise Linux Server Update Services For Sap Solutions=8.4
redhat Enterprise Linux Workstation=7.0
All of the following
redhat 3scale API Management=2.0
Any of the following
redhat Enterprise Linux=7.0
redhat Enterprise Linux=8.0
All of the following
redhat Codeready Linux Builder
Any of the following
redhat Enterprise Linux=8.0
redhat Enterprise Linux Eus=8.1
redhat Enterprise Linux Eus=8.2
redhat Enterprise Linux Eus=8.4
redhat Enterprise Linux For Power Little Endian=8.0
redhat Enterprise Linux For Power Little Endian Eus=8.1
redhat Enterprise Linux For Power Little Endian Eus=8.2
redhat Enterprise Linux For Power Little Endian Eus=8.4
All of the following
redhat Virtualization Host=4.0
Any of the following
redhat Enterprise Linux=7.0
redhat Enterprise Linux=8.0
redhat Software Collections
redhat Enterprise Linux Server=7.0
redhat 3scale API Management=2.0
redhat Enterprise Linux=7.0
redhat Enterprise Linux=8.0
redhat Codeready Linux Builder
redhat Enterprise Linux Eus=8.1
redhat Enterprise Linux Eus=8.2
redhat Enterprise Linux Eus=8.4
redhat Enterprise Linux For Power Little Endian=8.0
redhat Enterprise Linux For Power Little Endian Eus=8.1
redhat Enterprise Linux For Power Little Endian Eus=8.2
redhat Enterprise Linux For Power Little Endian Eus=8.4
redhat Virtualization Host=4.0
debian/linux
5.10.223-15.10.234-16.1.129-16.1.135-16.12.22-16.12.25-1
Remediation
Information
This vulnerability can be mitigated by disabling the nested virtualization feature:
```
# modprobe -r kvm_amd
# modprobe kvm_amd nested=0
```
Disabling VLS (Virtual VMLOAD/VMSAVE) is an alternative mitigation:
```
# modprobe kvm_amd vls=0
```
Mitigation
Disable nested virtualisation when loading the KVM AMD module:
modprobe kvm_amd nested=0
Event History
Aug 16, 2021
CVE Published
12:00 PM
Mar 4, 2022
CVE Published
via MITRE·06:41 PM
Data Sourced
via MITRE·06:41 PM
DescriptionWeakness
Jan 11, 2024
Data Sourced
via Launchpad·11:58 PM
Description
Apr 28, 2025
Data Sourced
via Ubuntu·04:30 AM
RemedyDescriptionSeverityAffected Software
Parent advisories
This vulnerability appears in the following advisories.
Frequently Asked Questions
1
What is the severity of CVE-2021-3656?
CVE-2021-3656 has been assigned a severity rating of medium, indicating a moderate risk to the affected systems.
2
How do I fix CVE-2021-3656?
To mitigate CVE-2021-3656, users should upgrade to the patched kernel versions provided by Red Hat.
3
What systems are affected by CVE-2021-3656?
CVE-2021-3656 affects various versions of the Red Hat Enterprise Linux kernel and other related Linux distributions.
4
Can CVE-2021-3656 be exploited remotely?
Yes, CVE-2021-3656 can potentially be exploited remotely if an attacker gains access to the virtual machine environment.
5
What is the nature of the vulnerability described in CVE-2021-3656?
CVE-2021-3656 involves improper validation of the 'virt_ext' field in KVM's AMD code for nested virtualization.