CVE-2026-23401

Description

In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE When installing an emulated MMIO SPTE, do so *after* dropping/zapping the existing SPTE (if it's shadow-present). While commit a54aa15c6bda3 was right about it being impossible to convert a shadow-present SPTE to an MMIO SPTE due to a _guest_ write, it failed to account for writes to guest memory that are outside the scope of KVM. E.g. if host userspace modifies a shadowed gPTE to switch from a memslot to emulted MMIO and then the guest hits a relevant page fault, KVM will install the MMIO SPTE without first zapping the shadow-present SPTE. ------------[ cut here ]------------ is_shadow_present_pte(*sptep) WARNING: arch/x86/kvm/mmu/mmu.c:484 at mark_mmio_spte+0xb2/0xc0 [kvm], CPU#0: vmx_ept_stale_r/4292 Modules linked in: kvm_intel kvm irqbypass CPU: 0 UID: 1000 PID: 4292 Comm: vmx_ept_stale_r Not tainted 7.0.0-rc2-eafebd2d2ab0-sink-vm #319 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:mark_mmio_spte+0xb2/0xc0 [kvm] Call Trace: <TASK> mmu_set_spte+0x237/0x440 [kvm] ept_page_fault+0x535/0x7f0 [kvm] kvm_mmu_do_page_fault+0xee/0x1f0 [kvm] kvm_mmu_page_fault+0x8d/0x620 [kvm] vmx_handle_exit+0x18c/0x5a0 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xc55/0x1c20 [kvm] kvm_vcpu_ioctl+0x2d5/0x980 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0xb5/0x730 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x47fa3f </TASK> ---[ end trace 0000000000000000 ]---

CVSS Details

CVSS Score

5.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

Linux Kernel (Prior to commit aad885e774966e97b675dfe928da164214a71605)

Linux Kernel (Prior to commit bce7fe59d43531623f3e43779127bfb33804925d)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

/*
 * PoC Concept for CVE-2026-23401
 * This requires a custom VMM or QEMU modification to trigger the race.
 */

#include <linux/kvm.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>

int main() {
    int kvm_fd = open("/dev/kvm", O_RDWR);
    int vm_fd = ioctl(kvm_fd, KVM_CREATE_VM, 0);
    // ... Setup VM and VCPU ...

    // 1. Map a guest page to a memslot (Normal Memory)
    // kvm_vm_ioctl(vm_fd, KVM_SET_USER_MEMORY_REGION, &region);

    // 2. Trigger a guest write to this page to establish shadow-present SPTE
    // run_guest_code(vcpu_fd);

    // 3. Host userspace modifies gPTE to switch region to MMIO
    // (e.g., via KVM_SET_USER_MEMORY_REGION with flags or dirty logging manipulation)
    // modify_memslot_to_mmio(vm_fd, region);

    // 4. Trigger guest access to the same address again
    // This causes KVM to install MMIO SPTE without zapping the old one.
    // run_guest_code(vcpu_fd);

    // Result: Kernel WARNING in mark_mmio_spte
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-23401
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-23401
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-23401/
[4] VulDB https://vuldb.com/cve/CVE-2026-23401
[5] https://git.kernel.org/stable/c/20656cd1f243d3a154aac5dd1b823110b6906fe1
[6] https://git.kernel.org/stable/c/459158151a158a6703b49f3c9de0e536d8bd553f
[7] https://git.kernel.org/stable/c/695320de6eadb75aaed8be1787c4ce4c189e4c7b
[8] https://git.kernel.org/stable/c/aad885e774966e97b675dfe928da164214a71605
[9] https://git.kernel.org/stable/c/bce7fe59d43531623f3e43779127bfb33804925d
[10] https://git.kernel.org/stable/c/ed5909992f344a7d3f4024261e9f751d9618a27d
[11] https://git.kernel.org/stable/c/fd28c5618699180cd69619801e9ae6a5266c0a22

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-23401", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-01T09:16:15.260", "lastModified": "2026-04-24T15:17:19.790", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE\n\nWhen installing an emulated MMIO SPTE, do so *after* dropping/zapping the\nexisting SPTE (if it's shadow-present). While commit a54aa15c6bda3 was\nright about it being impossible to convert a shadow-present SPTE to an\nMMIO SPTE due to a _guest_ write, it failed to account for writes to guest\nmemory that are outside the scope of KVM.\n\nE.g. if host userspace modifies a shadowed gPTE to switch from a memslot\nto emulted MMIO and then the guest hits a relevant page fault, KVM will\ninstall the MMIO SPTE without first zapping the shadow-present SPTE.\n\n ------------[ cut here ]------------\n is_shadow_present_pte(*sptep)\n WARNING: arch/x86/kvm/mmu/mmu.c:484 at mark_mmio_spte+0xb2/0xc0 [kvm], CPU#0: vmx_ept_stale_r/4292\n Modules linked in: kvm_intel kvm irqbypass\n CPU: 0 UID: 1000 PID: 4292 Comm: vmx_ept_stale_r Not tainted 7.0.0-rc2-eafebd2d2ab0-sink-vm #319 PREEMPT\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n RIP: 0010:mark_mmio_spte+0xb2/0xc0 [kvm]\n Call Trace:\n <TASK>\n mmu_set_spte+0x237/0x440 [kvm]\n ept_page_fault+0x535/0x7f0 [kvm]\n kvm_mmu_do_page_fault+0xee/0x1f0 [kvm]\n kvm_mmu_page_fault+0x8d/0x620 [kvm]\n vmx_handle_exit+0x18c/0x5a0 [kvm_intel]\n kvm_arch_vcpu_ioctl_run+0xc55/0x1c20 [kvm]\n kvm_vcpu_ioctl+0x2d5/0x980 [kvm]\n __x64_sys_ioctl+0x8a/0xd0\n do_syscall_64+0xb5/0x730\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\n RIP: 0033:0x47fa3f\n </TASK>\n ---[ end trace 0000000000000000 ]---"}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.13.1", "versionEndExcluding": "5.15.203", "matchCriteriaId": "CC3F58C6-09EC-41E6-8E82-613F5965C0DB"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.1.168", "matchCriteriaId": "E2DDDCA1-6DAB-4018-B920-8F045DDD8D3B"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.131", "matchCriteriaId": "CE6ED4D4-0046-4573-BFA9-D64143B6A89F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.80", "matchCriteriaId": "97EB19EC-A11E-49C6-9D2F-6F6EC6CB98B6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.21", "matchCriteriaId": "ED39847A-3B46-4729-B7CA-B2C30B9FA8FE"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.11", "matchCriteriaId": "4CA2E747-A9EC-4518-9AA2-B4247FC748B7"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:5.13:-:*:*:*:*:*:*", "matchCriteriaId": "8F0E7012-0BA3-4E6A-ADE9-57973CBDEE28"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*", "matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*", "matchCriteriaId": "4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*", "matchCriteriaId": "F666C8D8-6538-46D4-B318-87610DE64C34"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*", "matchCriteriaId": "02259FDA-961B-47BC-AE7F-93D7EC6E90C2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*", "matchCriteriaId": "58A9FEFF-C040-420D-8F0A-BFDAAA1DF258"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*", "matchCriteriaId": "1D2315C0-D46F-4F85-9754-F9E5E11374A6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc7:*:*:*:*:*:*", "matchCriteriaId": "512EE3A8-A590-4501-9A94-5D4B268D6 ... (truncated)