CVE-2021-3656 is a high-severity vulnerability in KVM's AMD SVM nested virtualization code, affecting Fedora, Linux, and Red Hat. It stems from improper validation of the "virt_ext" field in the VMCB, allowing a malicious L1 guest to disable critical intercepts for an L2 guest. This could lead to the L2 guest reading/writing host physical memory, resulting in system crashes, data leaks, or guest-to-host escape. The CVSS score is 8.8 (High), indicating a local attack vector with low complexity and high impact on confidentiality, integrity, and availability. There is no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage.
| Vendor | Product | Version(s) | CPE |
|---|---|---|---|
>= 4.13, < 4.14.245CPE matchmatch criteria | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | ||
>= 4.15, < 4.19.205CPE matchmatch criteria | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | ||
>= 4.20, < 5.4.142CPE matchmatch criteria | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | ||
>= 5.5, < 5.10.60CPE matchmatch criteria | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | ||
>= 5.11, < 5.13.12CPE matchmatch criteria | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
CVSS version used by this source: 3.1
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.2 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.
No media coverage found for this CVE.
The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.
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.
Mar 8, 2022kernel: SVM nested virtualization issue in KVM (VMLOAD/VMSAVE)
Aug 16, 2021