CVE-2026-64247
Received Received - Intake

Bounds Check Bypass in Linux Kernel KVM Hyper-V

Publication date: 2026-07-24

Last updated on: 2026-07-24

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: hyper-v: Bound the bank index when querying sparse banks When checking if a VP ID is included in a sparse bank set, explicitly check that the ID can actually be contained in a sparse bank (the TLFS allows for a maximum of 64 banks of 64 vCPUs each). When handling a paravirtual TLB flush for L2, the VP ID is copied verbatim from the enlightened VMCS, without any bounds check, i.e. isn't guaranteed to be under the limit of 4096. Failure to check the bounds of the VP ID leads to an out-of-bounds read when testing the sparse bank, and super strictly speaking could lead to KVM performing an unnecessary TLB flush for an L2 vCPU. ================================================================== BUG: KASAN: use-after-free in hv_is_vp_in_sparse_set+0x85/0x100 [kvm] Read of size 8 at addr ffff88811ba5f598 by task hyperv_evmcs/2802 CPU: 12 UID: 1000 PID: 2802 Comm: hyperv_evmcs Not tainted 7.1.0-rc2 #7 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Call Trace: <TASK> dump_stack_lvl+0x51/0x60 print_report+0xcb/0x5d0 kasan_report+0xb4/0xe0 kasan_check_range+0x35/0x1b0 hv_is_vp_in_sparse_set+0x85/0x100 [kvm] kvm_hv_flush_tlb+0xe9e/0x16c0 [kvm] kvm_hv_hypercall+0xe6b/0x1e60 [kvm] vmx_handle_exit+0x485/0x1b60 [kvm_intel] kvm_arch_vcpu_ioctl_run+0x22e3/0x5070 [kvm] kvm_vcpu_ioctl+0x5d0/0x10c0 [kvm] __x64_sys_ioctl+0x129/0x1a0 do_syscall_64+0xb9/0xcf0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f0e62d1a9bf </TASK> The buggy address belongs to the physical page: page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffffffffffffffff pfn:0x11ba5f flags: 0x4000000000000000(zone=1) raw: 4000000000000000 0000000000000000 00000000ffffffff 0000000000000000 raw: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff88811ba5f480: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ffff88811ba5f500: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff >ffff88811ba5f580: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ^ ffff88811ba5f600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ffff88811ba5f680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ================================================================== Disabling lock debugging due to kernel taint Opportunistically add a compile time assertion to ensure the maximum number of sparse banks exactly matches the number of possible bits in the passed in mask. [sean: add KASAN splat, drop comment, add assert, massage changelog]

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Meta Information

Published
2026-07-24
Last Modified
2026-07-24
Generated
2026-07-24
AI Q&A
2026-07-24
EPSS Evaluated
N/A
NVD
CVE-2026-64247
EUVD
EUVD-2026-48656

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel 7.1.0-rc2

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a vulnerability in the Linux kernel's KVM (Kernel-based Virtual Machine) component related to Hyper-V emulation. It involves a missing bounds check on a VP (Virtual Processor) ID when handling paravirtual TLB flushes for L2 virtual machines. The VP ID is copied directly from the enlightened VMCS without validation, potentially exceeding the allowed limit of 4096. This can lead to an out-of-bounds read when testing sparse banks, causing a use-after-free error detected by KASAN.

Detection Guidance

This vulnerability is specific to the Linux kernel's KVM hypervisor component and requires kernel-level detection. Check kernel logs for KASAN errors or use commands like dmesg | grep -i kasan or journalctl -k | grep -i kasan to identify use-after-free errors related to hyperv_evmcs or kvm_hv_flush_tlb.

Impact Analysis

This vulnerability could allow an attacker with access to a guest virtual machine to trigger a use-after-free condition in the host kernel. This may result in a denial-of-service (DoS) attack, causing the host system to crash or become unstable. It could also potentially lead to information disclosure or privilege escalation if exploited further.

Compliance Impact

This vulnerability is a kernel-level issue in the Linux KVM hypervisor affecting Hyper-V emulation. It does not directly impact compliance with GDPR, HIPAA, or similar standards as it is a technical flaw in memory handling during virtualization operations. Compliance risks would only arise if exploitation led to unauthorized data access or system compromise, which is not described in the provided context.

Mitigation Strategies

Apply the latest kernel patches from your Linux distribution to resolve the issue. If immediate patching is not possible, disable Hyper-V enlightenments in KVM guests by adding kvm-intel.vpid=0 or kvm-intel.ept=0 to kernel boot parameters and rebooting.

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