high
8.8
CWE
862
Advisory Published
CVE Published
CVE Published
Updated

CVE-2021-3656

First published: Tue 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 "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.

Credit: secalert@redhat.com

Affected SoftwareAffected VersionHow to fix
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
debian/linux
5.10.223-1
5.10.226-1
6.1.123-1
6.1.128-1
6.12.12-1
6.12.13-1
Linux Kernel>=4.13<4.14.245
Linux Kernel>=4.15<4.19.205
Linux Kernel>=4.20<5.4.142
Linux Kernel>=5.5<5.10.60
Linux Kernel>=5.11<5.13.12
Linux Kernel=5.14
Linux Kernel=5.14-rc1
Linux Kernel=5.14-rc2
Linux Kernel=5.14-rc3
Linux Kernel=5.14-rc4
Linux Kernel=5.14-rc5
Linux Kernel=5.14-rc6
Fedora=33
Fedora=34
All of
redhat software collections
redhat enterprise Linux server=7.0
redhat openstack=13
Red Hat 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
redhat 3scale api management=2.0
Any of
Red Hat Enterprise Linux=7.0
Red Hat Enterprise Linux=8.0
All of
redhat codeready Linux builder
Any of
Red Hat 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
redhat virtualization host=4.0
Any of
Red Hat Enterprise Linux=7.0
Red Hat Enterprise Linux=8.0
redhat software collections
redhat enterprise Linux server=7.0
redhat 3scale api management=2.0
Red Hat Enterprise Linux=7.0
Red Hat 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

Remedy

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 ```

Remedy

https://git.kernel.org/pub/scm/virt/kvm/kvm.git/commit/?id=c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc

Remedy

https://github.com/torvalds/linux/commit/c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc

Remedy

Disable nested virtualisation when loading the KVM AMD module: modprobe kvm_amd nested=0

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Reference Links

Parent vulnerabilities

(Appears in the following advisories)

Frequently Asked Questions

  • 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.

  • How do I fix CVE-2021-3656?

    To mitigate CVE-2021-3656, users should upgrade to the patched kernel versions provided by Red Hat.

  • 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.

  • 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.

  • 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.

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