# CVE-2026-99176: KVM: nVMX: Reset MMU back to the root MMU if loading L2 state fails for !VM-Entry

CVE-2026-99176 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-99176, released November 3, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-99176
- Priority: Routine
- CVSS: 4.7 (Moderate)
- EPSS: 0.0020
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 28, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-99176

## Description

In the Linux kernel, the following vulnerability has been resolved:  KVM: nVMX: Reset MMU back to the root MMU if loading L2 state fails for !VM-Entry  Reset the vCPU's MMU pointer back to the root MMU if loading L2 state fails in the "not from VM-Entry" case, i.e. when emulating RSM or handling KVM_SET_NESTED_STATE.  Failure to unwind the MMU pointer results in KVM trying to run L1 with a nested MMU, and is especially problematic if the vCPU manages to free its nested state before the VM crashes.  Constructing the root for a nested EPT MMU goes through vmcs12, which is dynamically allocated/freed when nVMX is enabled/disabled.  And so if the nested state is freed with the MMU still pointing at the nested MMU, KVM will hit a NULL pointer deref when attempting to get L1=>L2 EPTP.    BUG: kernel NULL pointer dereference, address: 0000000000000078   #PF: supervisor read access in kernel mode   #PF: error_code(0x0000) - not-present page   PGD 114a2d067 P4D 111743067 PUD 11141f067 PMD 0   Oops: Oops: 0000 [#1] SMP   CPU: 20 UID: 1000 PID: 1272 Comm: nested_tdp_faul Not tainted 7.3.0-rc4-8c89f11d1a99b-sink-vm #1914 PREEMPTLAZY   Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015   RIP: 0010:nested_ept_get_eptp+0xb/0x10 [kvm_intel]   Call Trace:    <TASK>    kvm_mmu_load+0xcd/0x870 [kvm]    kvm_arch_vcpu_ioctl_run+0x18f5/0x1f80 [kvm]    kvm_vcpu_ioctl+0x2c7/0x970 [kvm]    __x64_sys_ioctl+0x90/0xd0    do_syscall_64+0x9c/0x4d0    entry_SYSCALL_64_after_hwframe+0x4b/0x53   RIP: 0033:0x47491b    </TASK>   Modules linked in: kvm_intel kvm irqbypass   CR2: 0000000000000078   ---[ end trace 0000000000000000 ]---   RIP: 0010:nested_ept_get_eptp+0xb/0x10 [kvm_intel]  [sean: write changelog]

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-99176](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99176.md) | Nov 3, 2026 |
| Linux | linux Debian 14 | 7.2.13-1 | [DEBIAN-CVE-2026-99176](https://patchblox.com/security/data/fix/linux/debian-cve-2026-99176.md) | Nov 3, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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