Security restrictions bypass in Linux kernel - CVE-2021-3656

Vulnerability identifier: #VU56929

CSH Severity: Low

CVSSv4.0: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear

CVE-ID: CVE-2021-3656

CWE-ID: CWE-264

Exploitation vector: Local access

Exploit availability: No public exploit available

Vulnerable software:
Linux kernel

Software vendor:
Linux Foundation

The vulnerability allows a malicious guest to escalate privileges on the system.

The vulnerability exists due to improperly imposed security restrictions within 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.

The vulnerability allows the L2 guest 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.

Install updates from vendor's website.

• https://bugzilla.redhat.com/show_bug.cgi?id=1983988