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CVE-2025-40026 is a flaw in the Linux kernel KVM x86 subsystem affecting nested virtualization during emulation of an instruction that exits to userspace for I/O handling. After KVM had already committed to allowing an L2 guest I/O operation, the vulnerable logic could re-check L1 intercept state while completing the emulated userspace I/O path. If L1 or host userspace changed the I/O interception or permission bitmap state during that userspace exit, KVM could incorrectly reinterpret the already-emulated access as intercepted. This created inconsistent emulation state and could leave internal port-I/O tracking uncleared, evidenced by a WARN involving a non-zero vcpu->arch.pio.count in the emulator_pio_in_out path. The upstream fix changes KVM to recognize the emulation-completion path and avoid rechecking L1 intercepts at that stage.
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A Linux kernel KVM x86 vulnerability related to handling L1 intercept checks when completing userspace I/O.
A Linux kernel KVM x86 vulnerability described as improper handling of L1 intercept rechecks when completing userspace I/O.
A kernel KVM x86 vulnerability related to L1 intercept handling during userspace I/O completion.
A kernel KVM x86 vulnerability related to improper handling of L1 intercept rechecks during completion of userspace I/O.
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Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.