UBUNTU-CVE-2026-99176: Null Pointer Dereference
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 KVMSETNESTEDSTATE. 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: errorcode(0x0000) - not-present page PGD 114a2d067 P4D 111743067 PUD 11141f067 PMD 0 Oops: Oops: 0000 [#1] SMP CPU: 20 UID: 1000 PID: 1272 Comm: nestedtdpfaul 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:nestedeptgeteptp+0xb/0x10 [kvmintel] Call Trace: <TASK> kvmmmuload+0xcd/0x870 [kvm] kvmarchvcpuioctlrun+0x18f5/0x1f80 [kvm] kvmvcpuioctl+0x2c7/0x970 [kvm] x64sysioctl+0x90/0xd0 dosyscall64+0x9c/0x4d0 entrySYSCALL64afterhwframe+0x4b/0x53 RIP: 0033:0x47491b </TASK> Modules linked in: kvmintel kvm irqbypass CR2: 0000000000000078 ---[ end trace 0000000000000000 ]--- RIP: 0010:nestedeptgeteptp+0xb/0x10 [kvmintel] [sean: write changelog]
Affected Software
Event History
Frequently Asked Questions
Which systems are exposed to this issue?
Systems using KVM with nested VMX (nVMX) enabled are exposed when they emulate RSM or process KVM_SET_NESTED_STATE in the non-VM-Entry path. The affected Ubuntu kernel packages listed are linux, linux-azure, linux-gcp, linux-oracle, linux-aws-fips, linux-azure-fips, linux-fips, and linux-gcp-fips.
What can happen if the vulnerable path is triggered?
KVM can leave the vCPU using a nested MMU while running L1. If nested state is subsequently freed, a later attempt to construct the nested EPT MMU root can dereference a NULL vmcs12 pointer and crash the kernel.
How can the issue be mitigated before an update is available?
Avoid enabling or using nested VMX, and avoid workloads that invoke nested-state handling through KVM_SET_NESTED_STATE or RSM emulation. The reported failure depends on nested state being used and then freed while the MMU pointer remains set to the nested MMU.