CVE-2021-46977 (GCVE-0-2021-46977)

Vulnerability from cvelistv5 – Published: 2024-02-28 08:13 – Updated: 2026-08-05 08:45
VLAI
Title
KVM: VMX: Disable preemption when probing user return MSRs
Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: VMX: Disable preemption when probing user return MSRs Disable preemption when probing a user return MSR via RDSMR/WRMSR. If the MSR holds a different value per logical CPU, the WRMSR could corrupt the host's value if KVM is preempted between the RDMSR and WRMSR, and then rescheduled on a different CPU. Opportunistically land the helper in common x86, SVM will use the helper in a future commit.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-06-21 16:27 UTC
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6992 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 4be5341026246870818e28b53202b001426a5aec , < 31f29749ee970c251b3a7e5b914108425940d089 (git)
Affected: 4be5341026246870818e28b53202b001426a5aec , < 5adcdeb57007ccf8ab7ac20bf787ffb6fafb1a94 (git)
Affected: 4be5341026246870818e28b53202b001426a5aec , < e3ea1895df719c4ef87862501bb10d95f4177bed (git)
Affected: 4be5341026246870818e28b53202b001426a5aec , < 5104d7ffcf24749939bea7fdb5378d186473f890 (git)
guessed Create a notification for this product.
Linux Linux Affected: 5.5
Unaffected: 0 , < 5.5 (semver)
Unaffected: 5.10.38 , ≤ 5.10.* (semver)
Unaffected: 5.11.22 , ≤ 5.11.* (semver)
Unaffected: 5.12.5 , ≤ 5.12.* (semver)
Unaffected: 5.13 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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              "dateUpdated": "2024-08-04T05:24:38.401Z",
              "orgId": "af854a3a-2127-422b-91ae-364da2661108",
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                "url": "https://git.kernel.org/stable/c/5104d7ffcf24749939bea7fdb5378d186473f890"
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            ],
            "title": "CVE Program Container"
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            "metrics": [
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                "other": {
                  "content": {
                    "id": "CVE-2021-46977",
                    "options": [
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                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "no"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2024-06-21T16:27:41.559362Z",
                    "version": "2.0.3"
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              "dateUpdated": "2024-06-21T16:27:46.953Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
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              "defaultStatus": "unaffected",
              "product": "Linux",
              "programFiles": [
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                "arch/x86/kvm/vmx/vmx.c",
                "arch/x86/kvm/x86.c"
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              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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              "versions": [
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            {
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              "product": "Linux",
              "programFiles": [
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                "arch/x86/kvm/vmx/vmx.c",
                "arch/x86/kvm/x86.c"
              ],
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
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                  "status": "affected",
                  "version": "5.5"
                },
                {
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                  "status": "unaffected",
                  "version": "0",
                  "versionType": "semver"
                },
                {
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                  "status": "unaffected",
                  "version": "5.10.38",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.11.*",
                  "status": "unaffected",
                  "version": "5.11.22",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.12.*",
                  "status": "unaffected",
                  "version": "5.12.5",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "*",
                  "status": "unaffected",
                  "version": "5.13",
                  "versionType": "original_commit_for_fix"
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          ],
          "cpeApplicability": [
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                      "versionStartIncluding": "5.5",
                      "vulnerable": true
                    },
                    {
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              "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\u0027s 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."
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          ],
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                "baseSeverity": "HIGH",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
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                  "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\u0027s 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."
                }
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            "dateUpdated": "2026-08-05T08:45:21.421Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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            {
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      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2021-46977",
        "datePublished": "2024-02-28T08:13:08.489Z",
        "dateReserved": "2024-02-27T18:42:55.944Z",
        "dateUpdated": "2026-08-05T08:45:21.421Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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