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 (v2.0.3)
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 4be5341026246870818e28b53202b001426a5aec , < 31f29749ee970c251b3a7e5b914108425940d089 (git)
Affected: 4be5341026246870818e28b53202b001426a5aec , < 5adcdeb57007ccf8ab7ac20bf787ffb6fafb1a94 (git)
Affected: 4be5341026246870818e28b53202b001426a5aec , < e3ea1895df719c4ef87862501bb10d95f4177bed (git)
Affected: 4be5341026246870818e28b53202b001426a5aec , < 5104d7ffcf24749939bea7fdb5378d186473f890 (git)
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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)
Create a notification for this product.
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-04T21:37:58+00:00",
      "cve": "CVE-2021-46977",
      "id": "CVE-2021-46977",
      "initial_release_date": "2021-01-01T00:00:00+00:00",
      "product_status:known_affected": "42",
      "product_status:known_not_affected": "156",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: KVM: VMX: Disable preemption when probing user return MSRs",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-46977.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-07-31T01:34:47Z",
      "cve": "CVE-2021-46977",
      "id": "CVE-2021-46977",
      "initial_release_date": "2024-03-01T04:08:01Z",
      "product_status:known_not_affected": "292",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2021-46977",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2021-46977.json",
      "version": "17"
    },
    "vulnrichment": {
      "containers": "{\"adp\": [{\"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\"]}], \"providerMetadata\": {\"orgId\": \"af854a3a-2127-422b-91ae-364da2661108\", \"shortName\": \"CVE\", \"dateUpdated\": \"2024-08-04T05:24:38.401Z\"}}, {\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2021-46977\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2024-06-21T16:27:41.559362Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2024-06-21T16:27:46.953Z\"}}], \"cna\": {\"title\": \"KVM: VMX: Disable preemption when probing user return MSRs\", \"metrics\": [{\"cvssV3_1\": {\"version\": \"3.1\", \"baseScore\": 7.8, \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H\"}, \"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\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.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"4be5341026246870818e28b53202b001426a5aec\", \"lessThan\": \"31f29749ee970c251b3a7e5b914108425940d089\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"4be5341026246870818e28b53202b001426a5aec\", \"lessThan\": \"5adcdeb57007ccf8ab7ac20bf787ffb6fafb1a94\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"4be5341026246870818e28b53202b001426a5aec\", \"lessThan\": \"e3ea1895df719c4ef87862501bb10d95f4177bed\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"4be5341026246870818e28b53202b001426a5aec\", \"lessThan\": \"5104d7ffcf24749939bea7fdb5378d186473f890\", \"versionType\": \"git\"}], \"programFiles\": [\"arch/x86/include/asm/kvm_host.h\", \"arch/x86/kvm/vmx/vmx.c\", \"arch/x86/kvm/x86.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"5.5\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"5.5\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.10.38\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.11.22\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.11.*\"}, {\"status\": \"unaffected\", \"version\": \"5.12.5\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.12.*\"}, {\"status\": \"unaffected\", \"version\": \"5.13\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"arch/x86/include/asm/kvm_host.h\", \"arch/x86/kvm/vmx/vmx.c\", \"arch/x86/kvm/x86.c\"], \"defaultStatus\": \"affected\"}], \"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\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"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\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.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.38\", \"versionStartIncluding\": \"5.5\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.11.22\", \"versionStartIncluding\": \"5.5\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.12.5\", \"versionStartIncluding\": \"5.5\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.13\", \"versionStartIncluding\": \"5.5\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T08:45:21.421Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2021-46977\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-05T08:45:21.421Z\", \"dateReserved\": \"2024-02-27T18:42:55.944Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2024-02-28T08:13:08.489Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.