{"cve":"CVE-2021-3656","nvd":{"published":"2022-03-04T19:15:08.677","modified":"2026-06-17T04:05:30.877","status":"Modified","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H","score":8.8},"cwes":["CWE-862"],"references":["https://bugzilla.redhat.com/show_bug.cgi?id=1983988","https://git.kernel.org/pub/scm/virt/kvm/kvm.git/commit/?id=c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc","https://github.com/torvalds/linux/commit/c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc","https://www.openwall.com/lists/oss-security/2021/08/16/1","https://bugzilla.redhat.com/show_bug.cgi?id=1983988"],"products":["fedoraproject:fedora","linux:linux_kernel","redhat:3scale_api_management","redhat:codeready_linux_builder","redhat:enterprise_linux","redhat:enterprise_linux_desktop","redhat:enterprise_linux_eus","redhat:enterprise_linux_for_ibm_z_systems","redhat:enterprise_linux_for_ibm_z_systems_eus","redhat:enterprise_linux_for_power_big_endian","redhat:enterprise_linux_for_power_little_endian","redhat:enterprise_linux_for_power_little_endian_eus","redhat:enterprise_linux_for_real_time","redhat:enterprise_linux_for_real_time_for_nfv","redhat:enterprise_linux_for_real_time_for_nfv_tus","redhat:enterprise_linux_for_real_time_tus","redhat:enterprise_linux_for_scientific_computing","redhat:enterprise_linux_server","redhat:enterprise_linux_server_aus","redhat:enterprise_linux_server_for_power_little_endian_update_services_for_sap_solutions","redhat:enterprise_linux_server_tus","redhat:enterprise_linux_server_update_services_for_sap_solutions","redhat:enterprise_linux_workstation","redhat:openstack","redhat:software_collections","redhat:virtualization_host"],"source":"nvd","synced_at":"2026-10-19T21:28:04.509275555+00:00"},"epss":{"cve":"CVE-2021-3656","score":0.00658,"percentile":0.51486,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}