{ "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" ] } ] } ] } }