{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2021-46977","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2024-02-27T18:42:55.944Z","datePublished":"2024-02-28T08:13:08.489Z","dateUpdated":"2026-08-05T08:45:21.421Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-05T08:45:21.421Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: VMX: Disable preemption when probing user return MSRs\n\nDisable preemption when probing a user return MSR via RDSMR/WRMSR.  If\nthe MSR holds a different value per logical CPU, the WRMSR could corrupt\nthe host's value if KVM is preempted between the RDMSR and WRMSR, and\nthen rescheduled on a different CPU.\n\nOpportunistically land the helper in common x86, SVM will use the helper\nin a future commit."}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The vulnerable probe runs during KVM_CREATE_VCPU in vmx_create_vcpu, reachable only via local /dev/kvm ioctls (KVM_CREATE_VM then KVM_CREATE_VCPU), not from network packets or guest-only operations.\nAC:L - An attacker with KVM access can repeatedly create vCPUs while running concurrent vCPU threads and forcing migrations via affinity/load, so they can drive both the probe and the conditions that leave differing MSR values on CPUs; success does not depend on a victim-controlled state.\nPR:L - The kernel imposes no capability check on /dev/kvm; access is only file permission based, and common deployments (kvm group, nested virt, crosvm) grant this to unprivileged users, so root/admin is not required.\nUI:N - Exploitation requires only attacker-issued KVM ioctls; no separate victim action such as mounting a filesystem or opening a crafted file is needed.\nS:U - The attacker is already host userspace with KVM access; impact remains under the host kernel authority rather than a guest-to-host escape across a VM boundary.\nC:H - User-return MSRs (including LSTAR/TSC_AUX) can still hold guest values while kernel code runs, and the probe's raw WRMSR bypasses user-return tracking, so attacker-controlled guest MSR contents can be planted on another host CPU and enable SYSCALL-path hijacking and arbitrary host memory disclosure.\nI:H - Planting attacker-influenced syscall MSRs (especially LSTAR) onto a host CPU redirects subsequent host SYSCALL entry, which is exploitable for control-flow hijacking and arbitrary host integrity compromise beyond a simple per-CPU TSC_AUX mixup.\nA:H - Corrupting host user-return MSRs (wrong LSTAR/STAR/TSC_AUX) reliably breaks host syscall handling or CPU identity and can cause kernel oopses, panics, or hard system failure on the affected CPU."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/x86/include/asm/kvm_host.h","arch/x86/kvm/vmx/vmx.c","arch/x86/kvm/x86.c"],"versions":[{"version":"4be5341026246870818e28b53202b001426a5aec","lessThan":"31f29749ee970c251b3a7e5b914108425940d089","status":"affected","versionType":"git"},{"version":"4be5341026246870818e28b53202b001426a5aec","lessThan":"5adcdeb57007ccf8ab7ac20bf787ffb6fafb1a94","status":"affected","versionType":"git"},{"version":"4be5341026246870818e28b53202b001426a5aec","lessThan":"e3ea1895df719c4ef87862501bb10d95f4177bed","status":"affected","versionType":"git"},{"version":"4be5341026246870818e28b53202b001426a5aec","lessThan":"5104d7ffcf24749939bea7fdb5378d186473f890","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/x86/include/asm/kvm_host.h","arch/x86/kvm/vmx/vmx.c","arch/x86/kvm/x86.c"],"versions":[{"version":"5.5","status":"affected"},{"version":"0","lessThan":"5.5","status":"unaffected","versionType":"semver"},{"version":"5.10.38","lessThanOrEqual":"5.10.*","status":"unaffected","versionType":"semver"},{"version":"5.11.22","lessThanOrEqual":"5.11.*","status":"unaffected","versionType":"semver"},{"version":"5.12.5","lessThanOrEqual":"5.12.*","status":"unaffected","versionType":"semver"},{"version":"5.13","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.5","versionEndExcluding":"5.10.38"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.5","versionEndExcluding":"5.11.22"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.5","versionEndExcluding":"5.12.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.5","versionEndExcluding":"5.13"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/31f29749ee970c251b3a7e5b914108425940d089"},{"url":"https://git.kernel.org/stable/c/5adcdeb57007ccf8ab7ac20bf787ffb6fafb1a94"},{"url":"https://git.kernel.org/stable/c/e3ea1895df719c4ef87862501bb10d95f4177bed"},{"url":"https://git.kernel.org/stable/c/5104d7ffcf24749939bea7fdb5378d186473f890"}],"title":"KVM: VMX: Disable preemption when probing user return MSRs","x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2024-06-21T16:27:41.559362Z","id":"CVE-2021-46977","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2024-06-21T16:27:50.764Z"}},{"providerMetadata":{"orgId":"af854a3a-2127-422b-91ae-364da2661108","shortName":"CVE","dateUpdated":"2024-08-04T05:24:38.401Z"},"title":"CVE Program Container","references":[{"url":"https://git.kernel.org/stable/c/31f29749ee970c251b3a7e5b914108425940d089","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/5adcdeb57007ccf8ab7ac20bf787ffb6fafb1a94","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/e3ea1895df719c4ef87862501bb10d95f4177bed","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/5104d7ffcf24749939bea7fdb5378d186473f890","tags":["x_transferred"]}]}]}}