CVE-2026-23402

Description

In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Only WARN in direct MMUs when overwriting shadow-present SPTE Adjust KVM's sanity check against overwriting a shadow-present SPTE with a another SPTE with a different target PFN to only apply to direct MMUs, i.e. only to MMUs without shadowed gPTEs. While it's impossible for KVM to overwrite a shadow-present SPTE in response to a guest write, writes from outside the scope of KVM, e.g. from host userspace, aren't detected by KVM's write tracking and so can break KVM's shadow paging rules. ------------[ cut here ]------------ pfn != spte_to_pfn(*sptep) WARNING: arch/x86/kvm/mmu/mmu.c:3069 at mmu_set_spte+0x1e4/0x440 [kvm], CPU#0: vmx_ept_stale_r/872 Modules linked in: kvm_intel kvm irqbypass CPU: 0 UID: 1000 PID: 872 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:mmu_set_spte+0x1e4/0x440 [kvm] Call Trace: <TASK> 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 </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

cpe:2.3:o:linux:linux_kernel:6.16:-:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:* - VULNERABLE

Linux Kernel < 7.0.0-rc2

PoC / Exploit Code

⚠ For Security Research Only

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

python

/*
 * PoC Concept for CVE-2026-23402
 * Triggering SPTE overwrite warning in KVM.
 * Requires specific kernel config and KVM setup.
 */

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

int main() {
    int kvm_fd = open("/dev/kvm", O_RDWR);
    if (kvm_fd < 0) {
        perror("open /dev/kvm");
        return -1;
    }

    // Create VM and VCPU (Simplified)
    int vm_fd = ioctl(kvm_fd, KVM_CREATE_VM, 0);
    // ... Setup guest memory and run ...

    // The vulnerability is triggered by host userspace writes
    // that conflict with shadow-present SPTEs in direct MMUs.
    // This usually involves manipulating memory regions via KVM_SET_USER_MEMORY_REGION
    // while the guest is active to cause a mismatch in pfn checks.

    printf("Check dmesg for: WARNING: arch/x86/kvm/mmu/mmu.c\n");
    close(kvm_fd);
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-23402
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-23402
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-23402/
[4] VulDB https://vuldb.com/cve/CVE-2026-23402
[5] https://git.kernel.org/stable/c/a1e0f7150639bc30a8e75476d1c7daab77d44992
[6] https://git.kernel.org/stable/c/bab090e8fd5607f77379ea78b9d0c683cb1538a9
[7] https://git.kernel.org/stable/c/df83746075778958954aa0460cca55f4b3fc9c02

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-23402", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-01T09:16:15.670", "lastModified": "2026-04-24T15:17:03.090", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Only WARN in direct MMUs when overwriting shadow-present SPTE\n\nAdjust KVM's sanity check against overwriting a shadow-present SPTE with a\nanother SPTE with a different target PFN to only apply to direct MMUs,\ni.e. only to MMUs without shadowed gPTEs. While it's impossible for KVM\nto overwrite a shadow-present SPTE in response to a guest write, writes\nfrom outside the scope of KVM, e.g. from host userspace, aren't detected\nby KVM's write tracking and so can break KVM's shadow paging rules.\n\n ------------[ cut here ]------------\n pfn != spte_to_pfn(*sptep)\n WARNING: arch/x86/kvm/mmu/mmu.c:3069 at mmu_set_spte+0x1e4/0x440 [kvm], CPU#0: vmx_ept_stale_r/872\n Modules linked in: kvm_intel kvm irqbypass\n CPU: 0 UID: 1000 PID: 872 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:mmu_set_spte+0x1e4/0x440 [kvm]\n Call Trace:\n <TASK>\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 </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": "6.16.1", "versionEndExcluding": "6.18.21", "matchCriteriaId": "ABCE137D-81F5-4A69-BEC9-C222E10F0BAF"}, {"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:6.16:-:*:*:*:*:*:*", "matchCriteriaId": "6238B17D-C12B-458F-A138-97039BFC4595"}, {"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-A590-4501-9A94-5D4B268D6138"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/a1e0f7150639bc30a8e75476d1c7daab77d44992", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/bab090e8fd5607f77379ea78b9d0c683cb1538a9", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/df83746075778958954aa0460cca55f4b3fc9c02", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}