Cloudanix VulnDB

CVE-2024-40953

None

CVSS

—

EPSS

0.2%

Published

Jul 12, 2024

CISA due date

—

Cloudanix analysis

Monitor only SSVC: Track

A rare timing problem inside the Linux virtualization layer could let one virtual machine interfere with another or crash the host server, so organizations should update their Linux kernels soon.

Exploitation
Local Privilege
Attacker needs
Low Privilege
Complexity
Theoretical
Impact
Other
Component
OS kernel
Class
Race Condition
Remediation
Upgrade
Effort
Medium
Patch risk
Low

What it actually does

Data race on last_boosted_vcpu in kvm_vcpu_on_spin allows torn reads/writes that can produce an out-of-bounds index into the vCPU array when a 32-bit load overlaps a multi-byte store on systems with more than 256 vCPUs.

Why it matters to the business

Virtualization hosts running affected kernels may experience guest instability, crashes, or theoretically unauthorized memory access inside the hypervisor; the issue affects any Linux distribution using KVM and requires kernel upgrades across large fleets.

How an attack unfolds

An attacker would need to trigger concurrent kvm_vcpu_on_spin calls from multiple vCPUs while the compiler emits non-atomic stores; the resulting out-of-bounds array access could be used to read or write kernel memory, though the race window is extremely narrow and no public exploits are known.

How to fix it

Upgrade the Linux kernel to a version containing commit 11a772d5376aa6d3e2e69b5b5c585f79b60c0e17 or later; rebuild and reboot all affected hosts; apply vendor backports where available.

How to confirm the fix worked

Confirm the running kernel contains commit 11a772d5376aa6d3e2e69b5b5c585f79b60c0e17 via git log or package version; re-run KCSAN or similar data-race detectors on kvm_vcpu_on_spin to verify the READ_ONCE/WRITE_ONCE annotations are present.

Typical attack path

  1. Run multiple guests or vCPUs that contend on spin handling in kvm_vcpu_on_spin
  2. Trigger the data race on last_boosted_vcpu via concurrent pause exits
  3. Cause the compiler to emit torn 8-bit stores paired with a 32-bit load
  4. Obtain an index outside the valid vCPU range and dereference the vcpu_array
  5. Attempt to leverage the resulting out-of-bounds access for memory corruption or information disclosure

How to detect it

Search kernel logs and audit trails for KCSAN reports referencing kvm_vcpu_on_spin or last_boosted_vcpu; inspect crash dumps for out-of-bounds accesses involving vcpu_array; correlate with high-frequency pause-exit activity from guest workloads.

What your security team should do

  • Prioritize kernel updates on all KVM hosts within the next maintenance window
  • Monitor vendor advisories for distribution-specific backports of the fix commit
  • Enable kernel memory safety features such as KASAN and KCSAN in test environments to catch similar races
  • Review virtualization workload density to reduce vCPU counts below 256 where feasible until patched

The record

In the Linux kernel, the following vulnerability has been resolved: KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() Use {READ,WRITE}_ONCE() to access kvm->last_boosted_vcpu to ensure the loads and stores are atomic. In the extremely unlikely scenario the compiler tears the stores, it's theoretically possible for KVM to attempt to get a vCPU using an out-of-bounds index, e.g. if the write is split into multiple 8-bit stores, and is paired with a 32-bit load on a VM with 257 vCPUs: CPU0 CPU1 last_boosted_vcpu = 0xff; (last_boosted_vcpu = 0x100) last_boosted_vcpu[15:8] = 0x01; i = (last_boosted_vcpu = 0x1ff) last_boosted_vcpu[7:0] = 0x00; vcpu = kvm->vcpu_array[0x1ff]; As detected by KCSAN: BUG: KCSAN: data-race in kvm_vcpu_on_spin [kvm] / kvm_vcpu_on_spin [kvm] write to 0xffffc90025a92344 of 4 bytes by task 4340 on cpu 16: kvm_vcpu_on_spin (arch/x86/kvm/../../../virt/kvm/kvm_main.c:4112) kvm handle_pause (arch/x86/kvm/vmx/vmx.c:5929) kvm_intel vmx_handle_exit (arch/x86/kvm/vmx/vmx.c:? arch/x86/kvm/vmx/vmx.c:6606) kvm_intel vcpu_run (arch/x86/kvm/x86.c:11107 arch/x86/kvm/x86.c:11211) kvm kvm_arch_vcpu_ioctl_run (arch/x86/kvm/x86.c:?) kvm kvm_vcpu_ioctl (arch/x86/kvm/../../../virt/kvm/kvm_main.c:?) kvm __se_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:904 fs/ioctl.c:890) __x64_sys_ioctl (fs/ioctl.c:890) x64_sys_call (arch/x86/entry/syscall_64.c:33) do_syscall_64 (arch/x86/entry/common.c:?) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) read to 0xffffc90025a92344 of 4 bytes by task 4342 on cpu 4: kvm_vcpu_on_spin (arch/x86/kvm/../../../virt/kvm/kvm_main.c:4069) kvm handle_pause (arch/x86/kvm/vmx/vmx.c:5929) kvm_intel vmx_handle_exit (arch/x86/kvm/vmx/vmx.c:? arch/x86/kvm/vmx/vmx.c:6606) kvm_intel vcpu_run (arch/x86/kvm/x86.c:11107 arch/x86/kvm/x86.c:11211) kvm kvm_arch_vcpu_ioctl_run (arch/x86/kvm/x86.c:?) kvm kvm_vcpu_ioctl (arch/x86/kvm/../../../virt/kvm/kvm_main.c:?) kvm __se_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:904 fs/ioctl.c:890) __x64_sys_ioctl (fs/ioctl.c:890) x64_sys_call (arch/x86/entry/syscall_64.c:33) do_syscall_64 (arch/x86/entry/common.c:?) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) value changed: 0x00000012 -> 0x00000000

Affected packages

Ecosystem Package Introduced Fixed
Debian:11 linux 0 No fix
Debian:11 linux 0 5.10.234-1
Debian:11 linux-6.1 0 6.1.119-1~deb11u1
Debian:12 linux 0 6.1.99-1
Debian:13 linux 0 6.9.7-1
Debian:14 linux 0 6.9.7-1
Linux Kernel 2.6.39 4.19.323
SUSE:Linux Enterprise High Availability Extension 12 SP5 kernel-default 0 4.12.14-122.225.1
SUSE:Linux Enterprise High Availability Extension 15 SP5 kernel-default 0 5.14.21-150500.55.73.1
SUSE:Linux Enterprise High Availability Extension 15 SP6 kernel-default 0 6.4.0-150600.23.17.1
SUSE:Linux Enterprise Live Patching 12 SP5 kernel-default 0 4.12.14-122.225.1
SUSE:Linux Enterprise Live Patching 12 SP5 kgraft-patch-SLE12-SP5_Update_59 0 1-8.3.1
SUSE:Linux Enterprise Live Patching 15 SP5 kernel-default 0 5.14.21-150500.55.73.1
SUSE:Linux Enterprise Live Patching 15 SP5 kernel-livepatch-SLE15-SP5-RT_Update_18 0 1-150500.11.3.1
SUSE:Linux Enterprise Live Patching 15 SP5 kernel-livepatch-SLE15-SP5_Update_17 0 1-150500.11.3.1
SUSE:Linux Enterprise Live Patching 15 SP6 kernel-default 0 6.4.0-150600.23.17.1
SUSE:Linux Enterprise Live Patching 15 SP6 kernel-livepatch-SLE15-SP6-RT_Update_1 0 1-150600.1.5.1
SUSE:Linux Enterprise Live Patching 15 SP6 kernel-livepatch-SLE15-SP6_Update_3 0 1-150600.13.3.1
SUSE:Linux Enterprise Micro 5.5 kernel-default 0 5.14.21-150500.55.73.1
SUSE:Linux Enterprise Micro 5.5 kernel-default-base 0 5.14.21-150500.55.73.1.150500.6.33.8
SUSE:Linux Enterprise Micro 5.5 kernel-rt 0 5.14.21-150500.13.64.1
SUSE:Linux Enterprise Micro 5.5 kernel-source-rt 0 5.14.21-150500.13.64.1
SUSE:Linux Enterprise Module for Basesystem 15 SP5 kernel-64kb 0 5.14.21-150500.55.73.1
SUSE:Linux Enterprise Module for Basesystem 15 SP5 kernel-default 0 5.14.21-150500.55.73.1
SUSE:Linux Enterprise Module for Basesystem 15 SP5 kernel-default-base 0 5.14.21-150500.55.73.1.150500.6.33.8
SUSE:Linux Enterprise Module for Basesystem 15 SP5 kernel-source 0 5.14.21-150500.55.73.1
SUSE:Linux Enterprise Module for Basesystem 15 SP5 kernel-zfcpdump 0 5.14.21-150500.55.73.1
SUSE:Linux Enterprise Module for Basesystem 15 SP6 kernel-64kb 0 6.4.0-150600.23.17.1
SUSE:Linux Enterprise Module for Basesystem 15 SP6 kernel-default 0 6.4.0-150600.23.17.1
SUSE:Linux Enterprise Module for Basesystem 15 SP6 kernel-default-base 0 6.4.0-150600.23.17.1.150600.12.6.2
SUSE:Linux Enterprise Module for Basesystem 15 SP6 kernel-source 0 6.4.0-150600.23.17.1
SUSE:Linux Enterprise Module for Basesystem 15 SP6 kernel-zfcpdump 0 6.4.0-150600.23.17.1
SUSE:Linux Enterprise Module for Development Tools 15 SP5 kernel-docs 0 5.14.21-150500.55.73.2
SUSE:Linux Enterprise Module for Development Tools 15 SP5 kernel-obs-build 0 5.14.21-150500.55.73.1
SUSE:Linux Enterprise Module for Development Tools 15 SP5 kernel-source 0 5.14.21-150500.55.73.1
SUSE:Linux Enterprise Module for Development Tools 15 SP5 kernel-syms 0 5.14.21-150500.55.73.1
SUSE:Linux Enterprise Module for Development Tools 15 SP6 kernel-docs 0 6.4.0-150600.23.17.3
SUSE:Linux Enterprise Module for Development Tools 15 SP6 kernel-obs-build 0 6.4.0-150600.23.17.1
SUSE:Linux Enterprise Module for Development Tools 15 SP6 kernel-source 0 6.4.0-150600.23.17.1
SUSE:Linux Enterprise Module for Development Tools 15 SP6 kernel-syms 0 6.4.0-150600.23.17.1
SUSE:Linux Enterprise Module for Legacy 15 SP5 kernel-default 0 5.14.21-150500.55.73.1
SUSE:Linux Enterprise Module for Legacy 15 SP6 kernel-default 0 6.4.0-150600.23.17.1
SUSE:Linux Enterprise Module for Public Cloud 15 SP5 kernel-azure 0 5.14.21-150500.33.63.1
SUSE:Linux Enterprise Module for Public Cloud 15 SP5 kernel-source-azure 0 5.14.21-150500.33.63.1
SUSE:Linux Enterprise Module for Public Cloud 15 SP5 kernel-syms-azure 0 5.14.21-150500.33.63.1
SUSE:Linux Enterprise Module for Public Cloud 15 SP6 kernel-azure 0 6.4.0-150600.8.8.2
SUSE:Linux Enterprise Module for Public Cloud 15 SP6 kernel-source-azure 0 6.4.0-150600.8.8.2
SUSE:Linux Enterprise Module for Public Cloud 15 SP6 kernel-syms-azure 0 6.4.0-150600.8.8.1
SUSE:Linux Enterprise Real Time 12 SP5 kernel-rt 0 4.12.14-10.197.1
SUSE:Linux Enterprise Real Time 12 SP5 kernel-rt_debug 0 4.12.14-10.197.1
SUSE:Linux Enterprise Real Time 12 SP5 kernel-source-rt 0 4.12.14-10.197.1
SUSE:Linux Enterprise Real Time 12 SP5 kernel-syms-rt 0 4.12.14-10.197.1
SUSE:Linux Enterprise Server 12 SP5 kernel-azure 0 4.12.14-16.194.1
SUSE:Linux Enterprise Server 12 SP5 kernel-default 0 4.12.14-122.225.1
SUSE:Linux Enterprise Server 12 SP5 kernel-source 0 4.12.14-122.225.1
SUSE:Linux Enterprise Server 12 SP5 kernel-source-azure 0 4.12.14-16.194.1
SUSE:Linux Enterprise Server 12 SP5 kernel-syms 0 4.12.14-122.225.1
SUSE:Linux Enterprise Server 12 SP5 kernel-syms-azure 0 4.12.14-16.194.1
SUSE:Linux Enterprise Server for SAP Applications 12 SP5 kernel-azure 0 4.12.14-16.194.1
SUSE:Linux Enterprise Server for SAP Applications 12 SP5 kernel-default 0 4.12.14-122.225.1
SUSE:Linux Enterprise Server for SAP Applications 12 SP5 kernel-source 0 4.12.14-122.225.1
SUSE:Linux Enterprise Server for SAP Applications 12 SP5 kernel-source-azure 0 4.12.14-16.194.1
SUSE:Linux Enterprise Server for SAP Applications 12 SP5 kernel-syms 0 4.12.14-122.225.1
SUSE:Linux Enterprise Server for SAP Applications 12 SP5 kernel-syms-azure 0 4.12.14-16.194.1
SUSE:Linux Enterprise Software Development Kit 12 SP5 kernel-docs 0 4.12.14-122.225.2
SUSE:Linux Enterprise Software Development Kit 12 SP5 kernel-obs-build 0 4.12.14-122.225.1
SUSE:Linux Enterprise Workstation Extension 12 SP5 kernel-default 0 4.12.14-122.225.1
SUSE:Linux Enterprise Workstation Extension 15 SP5 kernel-default 0 5.14.21-150500.55.73.1
SUSE:Linux Enterprise Workstation Extension 15 SP6 kernel-default 0 6.4.0-150600.23.17.1
SUSE:Real Time Module 15 SP5 kernel-rt 0 5.14.21-150500.13.64.1
SUSE:Real Time Module 15 SP5 kernel-rt_debug 0 5.14.21-150500.13.64.1
SUSE:Real Time Module 15 SP5 kernel-source-rt 0 5.14.21-150500.13.64.1
SUSE:Real Time Module 15 SP5 kernel-syms-rt 0 5.14.21-150500.13.64.1
SUSE:Real Time Module 15 SP6 kernel-rt 0 6.4.0-150600.10.5.1
SUSE:Real Time Module 15 SP6 kernel-rt_debug 0 6.4.0-150600.10.5.1
SUSE:Real Time Module 15 SP6 kernel-source-rt 0 6.4.0-150600.10.5.1
SUSE:Real Time Module 15 SP6 kernel-syms-rt 0 6.4.0-150600.10.5.1
Ubuntu:16.04:LTS linux-hwe-edge 0 No fix
Ubuntu:18.04:LTS linux-aws-5.0 0 No fix
Ubuntu:18.04:LTS linux-aws-5.3 0 No fix
Ubuntu:18.04:LTS linux-azure 0 No fix
Ubuntu:18.04:LTS linux-azure-5.3 0 No fix
Ubuntu:18.04:LTS linux-azure-edge 0 No fix
Ubuntu:18.04:LTS linux-gcp 0 No fix
Ubuntu:18.04:LTS linux-gcp-5.3 0 No fix
Ubuntu:18.04:LTS linux-gke-4.15 0 No fix
Ubuntu:18.04:LTS linux-gke-5.4 0 No fix
Ubuntu:18.04:LTS linux-gkeop-5.4 0 No fix
Ubuntu:18.04:LTS linux-hwe 0 No fix
Ubuntu:18.04:LTS linux-hwe-edge 0 No fix
Ubuntu:18.04:LTS linux-oem 0 No fix
Ubuntu:18.04:LTS linux-oracle-5.0 0 No fix
Ubuntu:18.04:LTS linux-oracle-5.3 0 No fix
Ubuntu:20.04:LTS linux 0 No fix
Ubuntu:20.04:LTS linux 0 5.4.0-208.228
Ubuntu:20.04:LTS linux-aws 0 No fix
Ubuntu:20.04:LTS linux-aws 0 5.4.0-1140.150
Ubuntu:20.04:LTS linux-aws-5.11 0 No fix
Ubuntu:20.04:LTS linux-aws-5.13 0 No fix
Ubuntu:20.04:LTS linux-aws-5.15 0 No fix
Ubuntu:20.04:LTS linux-aws-5.15 0 5.15.0-1080.87~20.04.1
Ubuntu:20.04:LTS linux-aws-5.8 0 No fix
Ubuntu:20.04:LTS linux-azure 0 No fix
Ubuntu:20.04:LTS linux-azure 0 5.4.0-1145.152
Ubuntu:20.04:LTS linux-azure-5.11 0 No fix
Ubuntu:20.04:LTS linux-azure-5.13 0 No fix
Ubuntu:20.04:LTS linux-azure-5.15 0 No fix
Ubuntu:20.04:LTS linux-azure-5.15 0 5.15.0-1081.90~20.04.1
Ubuntu:20.04:LTS linux-azure-5.8 0 No fix
Ubuntu:20.04:LTS linux-azure-fde 0 No fix
Ubuntu:20.04:LTS linux-azure-fde-5.15 0 No fix
Ubuntu:20.04:LTS linux-bluefield 0 No fix
Ubuntu:20.04:LTS linux-bluefield 0 5.4.0-1099.106
Ubuntu:20.04:LTS linux-gcp 0 No fix
Ubuntu:20.04:LTS linux-gcp 0 5.4.0-1143.152
Ubuntu:20.04:LTS linux-gcp-5.11 0 No fix
Ubuntu:20.04:LTS linux-gcp-5.13 0 No fix
Ubuntu:20.04:LTS linux-gcp-5.15 0 No fix
Ubuntu:20.04:LTS linux-gcp-5.15 0 5.15.0-1077.86~20.04.1
Ubuntu:20.04:LTS linux-gcp-5.8 0 No fix
Ubuntu:20.04:LTS linux-gke 0 No fix
Ubuntu:20.04:LTS linux-gke-5.15 0 No fix
Ubuntu:20.04:LTS linux-gkeop 0 No fix
Ubuntu:20.04:LTS linux-gkeop-5.15 0 No fix
Ubuntu:20.04:LTS linux-hwe-5.11 0 No fix
Ubuntu:20.04:LTS linux-hwe-5.13 0 No fix
Ubuntu:20.04:LTS linux-hwe-5.15 0 No fix
Ubuntu:20.04:LTS linux-hwe-5.15 0 5.15.0-134.145~20.04.1
Ubuntu:20.04:LTS linux-hwe-5.8 0 No fix
Ubuntu:20.04:LTS linux-ibm 0 No fix
Ubuntu:20.04:LTS linux-ibm 0 5.4.0-1086.91
Ubuntu:20.04:LTS linux-ibm-5.15 0 No fix
Ubuntu:20.04:LTS linux-ibm-5.15 0 5.15.0-1074.77~20.04.1
Ubuntu:20.04:LTS linux-intel-5.13 0 No fix
Ubuntu:20.04:LTS linux-intel-iotg-5.15 0 No fix
Ubuntu:20.04:LTS linux-intel-iotg-5.15 0 5.15.0-1073.79~20.04.2
Ubuntu:20.04:LTS linux-iot 0 No fix
Ubuntu:20.04:LTS linux-iot 0 5.4.0-1048.51
Ubuntu:20.04:LTS linux-kvm 0 No fix
Ubuntu:20.04:LTS linux-kvm 0 5.4.0-1127.136
Ubuntu:20.04:LTS linux-lowlatency-hwe-5.15 0 No fix
Ubuntu:20.04:LTS linux-lowlatency-hwe-5.15 0 5.15.0-133.143~20.04.1
Ubuntu:20.04:LTS linux-oem-5.10 0 No fix
Ubuntu:20.04:LTS linux-oem-5.13 0 No fix
Ubuntu:20.04:LTS linux-oem-5.14 0 No fix
Ubuntu:20.04:LTS linux-oem-5.6 0 No fix
Ubuntu:20.04:LTS linux-oracle 0 No fix
Ubuntu:20.04:LTS linux-oracle 0 5.4.0-1138.147
Ubuntu:20.04:LTS linux-oracle-5.11 0 No fix
Ubuntu:20.04:LTS linux-oracle-5.13 0 No fix
Ubuntu:20.04:LTS linux-oracle-5.15 0 No fix
Ubuntu:20.04:LTS linux-oracle-5.15 0 5.15.0-1075.81~20.04.1
Ubuntu:20.04:LTS linux-oracle-5.8 0 No fix
Ubuntu:20.04:LTS linux-raspi 0 No fix
Ubuntu:20.04:LTS linux-raspi 0 5.4.0-1129.142
Ubuntu:20.04:LTS linux-raspi2 0 No fix
Ubuntu:20.04:LTS linux-riscv 0 No fix
Ubuntu:20.04:LTS linux-riscv-5.11 0 No fix
Ubuntu:20.04:LTS linux-riscv-5.15 0 No fix
Ubuntu:20.04:LTS linux-riscv-5.15 0 5.15.0-1073.77~20.04.1
Ubuntu:20.04:LTS linux-riscv-5.8 0 No fix
Ubuntu:20.04:LTS linux-xilinx-zynqmp 0 No fix
Ubuntu:20.04:LTS linux-xilinx-zynqmp 0 5.4.0-1058.62
Ubuntu:22.04:LTS linux 0 No fix
Ubuntu:22.04:LTS linux 0 5.15.0-133.144
Ubuntu:22.04:LTS linux-allwinner-5.19 0 No fix
Ubuntu:22.04:LTS linux-aws 0 No fix
Ubuntu:22.04:LTS linux-aws 0 5.15.0-1078.85
Ubuntu:22.04:LTS linux-aws-5.19 0 No fix
Ubuntu:22.04:LTS linux-aws-6.2 0 No fix
Ubuntu:22.04:LTS linux-aws-6.5 0 No fix
Ubuntu:22.04:LTS linux-aws-6.8 0 6.8.0-1015.16~22.04.1
Ubuntu:22.04:LTS linux-azure 0 No fix
Ubuntu:22.04:LTS linux-azure 0 5.15.0-1081.90
Ubuntu:22.04:LTS linux-azure-5.19 0 No fix
Ubuntu:22.04:LTS linux-azure-6.2 0 No fix
Ubuntu:22.04:LTS linux-azure-6.5 0 No fix
Ubuntu:22.04:LTS linux-azure-6.8 0 No fix
Ubuntu:22.04:LTS linux-azure-6.8 0 6.8.0-1014.16~22.04.1
Ubuntu:22.04:LTS linux-azure-fde 0 No fix
Ubuntu:22.04:LTS linux-azure-fde 0 5.15.0-1081.90.1
Ubuntu:22.04:LTS linux-azure-fde-5.19 0 No fix
Ubuntu:22.04:LTS linux-azure-fde-6.2 0 No fix
Ubuntu:22.04:LTS linux-gcp 0 No fix
Ubuntu:22.04:LTS linux-gcp 0 5.15.0-1077.86
Ubuntu:22.04:LTS linux-gcp-5.19 0 No fix
Ubuntu:22.04:LTS linux-gcp-6.2 0 No fix
Ubuntu:22.04:LTS linux-gcp-6.5 0 No fix
Ubuntu:22.04:LTS linux-gcp-6.8 0 6.8.0-1014.16~22.04.1
Ubuntu:22.04:LTS linux-gke 0 No fix
Ubuntu:22.04:LTS linux-gke 0 5.15.0-1075.81
Ubuntu:22.04:LTS linux-gkeop 0 No fix
Ubuntu:22.04:LTS linux-gkeop 0 5.15.0-1060.68
Ubuntu:22.04:LTS linux-hwe-5.19 0 No fix
Ubuntu:22.04:LTS linux-hwe-6.2 0 No fix
Ubuntu:22.04:LTS linux-hwe-6.5 0 No fix
Ubuntu:22.04:LTS linux-hwe-6.8 0 6.8.0-45.45~22.04.1
Ubuntu:22.04:LTS linux-ibm 0 No fix
Ubuntu:22.04:LTS linux-ibm 0 5.15.0-1070.73
Ubuntu:22.04:LTS linux-ibm-6.8 0 6.8.0-1012.12~22.04.1

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