{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2024-40953","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2024-07-12T12:17:45.592Z","datePublished":"2024-07-12T12:31:56.832Z","dateUpdated":"2026-08-05T11:34:12.855Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-05T11:34:12.855Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin()\n\nUse {READ,WRITE}_ONCE() to access kvm->last_boosted_vcpu to ensure the\nloads and stores are atomic.  In the extremely unlikely scenario the\ncompiler tears the stores, it's theoretically possible for KVM to attempt\nto get a vCPU using an out-of-bounds index, e.g. if the write is split\ninto multiple 8-bit stores, and is paired with a 32-bit load on a VM with\n257 vCPUs:\n\n  CPU0                              CPU1\n  last_boosted_vcpu = 0xff;\n\n                                    (last_boosted_vcpu = 0x100)\n                                    last_boosted_vcpu[15:8] = 0x01;\n  i = (last_boosted_vcpu = 0x1ff)\n                                    last_boosted_vcpu[7:0] = 0x00;\n\n  vcpu = kvm->vcpu_array[0x1ff];\n\nAs detected by KCSAN:\n\n  BUG: KCSAN: data-race in kvm_vcpu_on_spin [kvm] / kvm_vcpu_on_spin [kvm]\n\n  write to 0xffffc90025a92344 of 4 bytes by task 4340 on cpu 16:\n  kvm_vcpu_on_spin (arch/x86/kvm/../../../virt/kvm/kvm_main.c:4112) kvm\n  handle_pause (arch/x86/kvm/vmx/vmx.c:5929) kvm_intel\n  vmx_handle_exit (arch/x86/kvm/vmx/vmx.c:?\n\t\t arch/x86/kvm/vmx/vmx.c:6606) kvm_intel\n  vcpu_run (arch/x86/kvm/x86.c:11107 arch/x86/kvm/x86.c:11211) kvm\n  kvm_arch_vcpu_ioctl_run (arch/x86/kvm/x86.c:?) kvm\n  kvm_vcpu_ioctl (arch/x86/kvm/../../../virt/kvm/kvm_main.c:?) kvm\n  __se_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:904 fs/ioctl.c:890)\n  __x64_sys_ioctl (fs/ioctl.c:890)\n  x64_sys_call (arch/x86/entry/syscall_64.c:33)\n  do_syscall_64 (arch/x86/entry/common.c:?)\n  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)\n\n  read to 0xffffc90025a92344 of 4 bytes by task 4342 on cpu 4:\n  kvm_vcpu_on_spin (arch/x86/kvm/../../../virt/kvm/kvm_main.c:4069) kvm\n  handle_pause (arch/x86/kvm/vmx/vmx.c:5929) kvm_intel\n  vmx_handle_exit (arch/x86/kvm/vmx/vmx.c:?\n\t\t\tarch/x86/kvm/vmx/vmx.c:6606) kvm_intel\n  vcpu_run (arch/x86/kvm/x86.c:11107 arch/x86/kvm/x86.c:11211) kvm\n  kvm_arch_vcpu_ioctl_run (arch/x86/kvm/x86.c:?) kvm\n  kvm_vcpu_ioctl (arch/x86/kvm/../../../virt/kvm/kvm_main.c:?) kvm\n  __se_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:904 fs/ioctl.c:890)\n  __x64_sys_ioctl (fs/ioctl.c:890)\n  x64_sys_call (arch/x86/entry/syscall_64.c:33)\n  do_syscall_64 (arch/x86/entry/common.c:?)\n  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)\n\n  value changed: 0x00000012 -> 0x00000000"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H","baseScore":7.9,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The vulnerable code is entered only from guest execution of PAUSE/WFE/DIAG-0x44 handled by the host KVM module, or equivalently via the `KVM_RUN` ioctl on `/dev/kvm` as shown in the KCSAN stack trace. There is no network-facing path to `kvm_vcpu_on_spin()`, so the attacker must be running code locally on the host or inside a VM hosted on it.\nAC:L - The attacker controls both sides of the race outright — a guest simply runs PAUSE spin loops on several vCPUs at once, driving many threads into the unsynchronized read/write of `kvm->last_boosted_vcpu` with no external precondition. No specific victim state or memory layout the attacker cannot influence is required to hit the racing accesses.\nPR:L - The attacker needs the ability to run code inside a VM on the host (or open `/dev/kvm` locally), which is an unprivileged-user-level capability — no root or CAP_SYS_ADMIN is required, and PAUSE is executable from guest ring 3. This matches the standard treatment of guest-triggerable KVM host bugs.\nUI:N - Triggering requires only that the attacker's own guest vCPU threads spin concurrently; no host administrator or other user has to perform any action. The race is hit entirely by the attacker's own execution.\nS:C - The bug is triggered by unprivileged code inside a guest but the corrupted index and any resulting wild pointer access occur in the host kernel, crossing the VM-to-hypervisor security boundary. A guest compromising host kernel availability/integrity is a scope change.\nC:L - A torn value yields an out-of-bounds vCPU index, causing the host to read a pointer-sized slot past the vCPU array and then dereference it (`vcpu->ready`, `vcpu->preempted`, `target->pid`), touching host kernel memory outside the intended object. The read value is never returned to the guest and the offset is not attacker-chosen, so this is a limited disclosure rather than an arbitrary read primitive.\nI:L - `kvm_vcpu_eligible_for_directed_yield()` writes `vcpu->spin_loop.dy_eligible` through the same unvalidated pointer, giving a fixed-offset host-kernel write via an out-of-bounds vCPU reference, and the bogus target also perturbs host scheduling through `yield_to()`. The written value and target address are not attacker-controlled, limiting this to bounded corruption rather than a control-flow hijack primitive.\nA:H - Per the upstream changelog, the torn access lets KVM fetch a vCPU with an out-of-bounds index; the resulting NULL or garbage pointer is dereferenced without any validation, oopsing or panicking the host kernel. A guest crashing the hypervisor takes down the host and every other VM on it."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["virt/kvm/kvm_main.c"],"versions":[{"version":"217ece6129f2d3b4fdd18d9e79be9e43d8d14a42","lessThan":"11a772d5376aa6d3e2e69b5b5c585f79b60c0e17","status":"affected","versionType":"git"},{"version":"217ece6129f2d3b4fdd18d9e79be9e43d8d14a42","lessThan":"4c141136a28421b78f34969b25a4fa32e06e2180","status":"affected","versionType":"git"},{"version":"217ece6129f2d3b4fdd18d9e79be9e43d8d14a42","lessThan":"71fbc3af3dacb26c3aa2f30bb3ab05c44d082c84","status":"affected","versionType":"git"},{"version":"217ece6129f2d3b4fdd18d9e79be9e43d8d14a42","lessThan":"82bd728a06e55f5b5f93d10ce67f4fe7e689853a","status":"affected","versionType":"git"},{"version":"217ece6129f2d3b4fdd18d9e79be9e43d8d14a42","lessThan":"92c77807d938145c7c3350c944ef9f39d7f6017c","status":"affected","versionType":"git"},{"version":"217ece6129f2d3b4fdd18d9e79be9e43d8d14a42","lessThan":"a937ef951bba72f48d2402451419d725d70dba20","status":"affected","versionType":"git"},{"version":"217ece6129f2d3b4fdd18d9e79be9e43d8d14a42","lessThan":"95c8dd79f3a14df96b3820b35b8399bd91b2be60","status":"affected","versionType":"git"},{"version":"217ece6129f2d3b4fdd18d9e79be9e43d8d14a42","lessThan":"49f683b41f28918df3e51ddc0d928cb2e934ccdb","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["virt/kvm/kvm_main.c"],"versions":[{"version":"2.6.39","status":"affected"},{"version":"0","lessThan":"2.6.39","status":"unaffected","versionType":"semver"},{"version":"4.19.323","lessThanOrEqual":"4.19.*","status":"unaffected","versionType":"semver"},{"version":"5.4.285","lessThanOrEqual":"5.4.*","status":"unaffected","versionType":"semver"},{"version":"5.10.228","lessThanOrEqual":"5.10.*","status":"unaffected","versionType":"semver"},{"version":"5.15.169","lessThanOrEqual":"5.15.*","status":"unaffected","versionType":"semver"},{"version":"6.1.96","lessThanOrEqual":"6.1.*","status":"unaffected","versionType":"semver"},{"version":"6.6.36","lessThanOrEqual":"6.6.*","status":"unaffected","versionType":"semver"},{"version":"6.9.7","lessThanOrEqual":"6.9.*","status":"unaffected","versionType":"semver"},{"version":"6.10","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":"2.6.39","versionEndExcluding":"4.19.323"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.39","versionEndExcluding":"5.4.285"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.39","versionEndExcluding":"5.10.228"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.39","versionEndExcluding":"5.15.169"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.39","versionEndExcluding":"6.1.96"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.39","versionEndExcluding":"6.6.36"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.39","versionEndExcluding":"6.9.7"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.39","versionEndExcluding":"6.10"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/11a772d5376aa6d3e2e69b5b5c585f79b60c0e17"},{"url":"https://git.kernel.org/stable/c/4c141136a28421b78f34969b25a4fa32e06e2180"},{"url":"https://git.kernel.org/stable/c/71fbc3af3dacb26c3aa2f30bb3ab05c44d082c84"},{"url":"https://git.kernel.org/stable/c/82bd728a06e55f5b5f93d10ce67f4fe7e689853a"},{"url":"https://git.kernel.org/stable/c/92c77807d938145c7c3350c944ef9f39d7f6017c"},{"url":"https://git.kernel.org/stable/c/a937ef951bba72f48d2402451419d725d70dba20"},{"url":"https://git.kernel.org/stable/c/95c8dd79f3a14df96b3820b35b8399bd91b2be60"},{"url":"https://git.kernel.org/stable/c/49f683b41f28918df3e51ddc0d928cb2e934ccdb"}],"title":"KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin()","x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CVE Program Container","references":[{"url":"https://git.kernel.org/stable/c/92c77807d938145c7c3350c944ef9f39d7f6017c","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/a937ef951bba72f48d2402451419d725d70dba20","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/95c8dd79f3a14df96b3820b35b8399bd91b2be60","tags":["x_transferred"]},{"url":"https://git.kernel.org/stable/c/49f683b41f28918df3e51ddc0d928cb2e934ccdb","tags":["x_transferred"]},{"url":"https://lists.debian.org/debian-lts-announce/2025/03/msg00002.html"},{"url":"https://lists.debian.org/debian-lts-announce/2025/01/msg00001.html"}],"providerMetadata":{"orgId":"af854a3a-2127-422b-91ae-364da2661108","shortName":"CVE","dateUpdated":"2025-11-03T21:58:17.097Z"}},{"metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2024-40953","role":"CISA 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