CVE-2026-46295
MediumCVSS 5.5Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
A bug was found in the Linux kernel's KVM for x86, where __kvm_apic_update_irr skips scanning IRR when PID.ON is set but PIR is empty. This triggers a false WARNING in vmx_check_nested_events() and causes unnecessary L2 VM-Enter/VM-Exit cycles.
Risk Assessment
The risk is performance degradation in nested virtualization environments and misleading warnings that can complicate diagnostics and lead to wasted VM-Enter/VM-Exit cycles.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit addressing the issue in __kvm_apic_update_irr). If an update is not possible, monitor nested virtualization environments for WARNING occurrences.
Other vulnerabilities in Linux kernel
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- CVE-2026-99280Unknown
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- CVE-2026-99258Unknown
In the Linux kernel, hv_apicid_to_vp_index() uses per-CPU hypercall input and output pages. In an SEV-SNP CoCo VM without a paravisor the output page is not allocated, so the hypervisor stores the resulting VP index into memory not allocated by the guest. The fix uses the input page for both input and output.
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In the Linux kernel, init_vp_index() contains a retry loop that strips CPUs from a node if they are already in the allocated cpumask or outside the HK_TYPE_MANAGED_IRQ housekeeping cpumask. If the housekeeping cpumask contains no CPU in that node, the loop becomes infinite. The fix skips NUMA nodes with no housekeeping CPU and aborts early when no online housekeeping CPUs exist.
- CVE-2026-99250Unknown
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Do IRR scan in __kvm_apic_update_irr even if PIR is empty Fall back to apic_find_highest_vector() when PID.ON is set but PIR turns out to be empty, to correctly report the highest pending interrupt from the existing IRR. In a nested VM stress test, the following WARNING fires in vmx_check_nested_events() when kvm_cpu_has_interrupt() reports a pending interrupt but the subsequent kvm_apic_has_interrupt() (which invokes vmx_sync_pir_to_irr() again) returns -1: WARNING: CPU: 99 PID: 57767 at arch/x86/kvm/vmx/nested.c:4449 vmx_check_nested_events+0x6bf/0x6e0 [kvm_intel] Call Trace: kvm_check_and_inject_events vcpu_enter_guest.constprop.0 vcpu_run kvm_arch_vcpu_ioctl_run kvm_vcpu_ioctl __x64_sys_ioctl do_syscall_64 entry_SYSCALL_64_after_hwframe The root cause is a race between vmx_sync_pir_to_irr() on the target vCPU and __vmx_deliver_posted_interrupt() on a sender vCPU. The sender performs two individually-atomic operations that are not a single transaction: 1. pi_test_and_set_pir(vector) -- sets the PIR bit 2. pi_test_and_set_on() -- sets PID.ON The following interleaving triggers the bug: Sender vCPU (IPI): Target vCPU (1st sync_pir_to_irr): B1: set PIR[vector] A1: pi_clear_on() A2: pi_harvest_pir() -> sees B1 bit A3: xchg() -> consumes bit, PIR=0 (1st sync returns correct max_irr) B2: set PID.ON = 1 Target vCPU (2nd sync_pir_to_irr): C1: pi_test_on() -> TRUE (from B2) C2: pi_clear_on() -> ON=0 C3: pi_harvest_pir() -> PIR empty C4: *max_irr = -1, early return IRR NOT SCANNED The interrupt is not lost (it resides in the IRR from the first sync and is recovered on the next vcpu_enter_guest() iteration), but the incorrect max_irr causes a spurious WARNING and a wasted L2 VM-Enter/VM-Exit cycle.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

