CVE-2023-53756

Description

In the Linux kernel, the following vulnerability has been resolved: KVM: VMX: Fix crash due to uninitialized current_vmcs KVM enables 'Enlightened VMCS' and 'Enlightened MSR Bitmap' when running as a nested hypervisor on top of Hyper-V. When MSR bitmap is updated, evmcs_touch_msr_bitmap function uses current_vmcs per-cpu variable to mark that the msr bitmap was changed. vmx_vcpu_create() modifies the msr bitmap via vmx_disable_intercept_for_msr -> vmx_msr_bitmap_l01_changed which in the end calls this function. The function checks for current_vmcs if it is null but the check is insufficient because current_vmcs is not initialized. Because of this, the code might incorrectly write to the structure pointed by current_vmcs value left by another task. Preemption is not disabled, the current task can be preempted and moved to another CPU while current_vmcs is accessed multiple times from evmcs_touch_msr_bitmap() which leads to crash. The manipulation of MSR bitmaps by callers happens only for vmcs01 so the solution is to use vmx->vmcs01.vmcs instead of current_vmcs. BUG: kernel NULL pointer dereference, address: 0000000000000338 PGD 4e1775067 P4D 0 Oops: 0002 [#1] PREEMPT SMP NOPTI ... RIP: 0010:vmx_msr_bitmap_l01_changed+0x39/0x50 [kvm_intel] ... Call Trace: vmx_disable_intercept_for_msr+0x36/0x260 [kvm_intel] vmx_vcpu_create+0xe6/0x540 [kvm_intel] kvm_arch_vcpu_create+0x1d1/0x2e0 [kvm] kvm_vm_ioctl_create_vcpu+0x178/0x430 [kvm] kvm_vm_ioctl+0x53f/0x790 [kvm] __x64_sys_ioctl+0x8a/0xc0 do_syscall_64+0x5c/0x90 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Gravité et risque d'exploitation

CVE-2023-53756 obtient un score CVSS de 0.0/10, soit une gravité non évaluée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.19 %, ce qui la place devant 8.3 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <=6.1.*, <6e7bc50f97c9855da83f1478f722590defd45ff2, 6.1.16, 0, <93827a0a36396f2fd6368a54a020f420c8916e9b, 5.15.103, <=5.10.*, 6.2.3, 6.3, <b2de2b4d4e007f9add46ea8dc06f781835e3ea9f, ceef7d10dfb6284d512c499292e6daa35ea83f90, <6baebcecf09acd19e2bab1c2911dcdba5d48a1dc, <=6.2.*, 5.10.175, <4.18, 4.18, <=*, <=5.15.*, <3ba95cc671c025d0d2a1c7d5e2930f0ff0980cf4) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/6baebcecf09acd19e2bab1c2911dcdba5d48a1dc
• https://git.kernel.org/stable/c/6e7bc50f97c9855da83f1478f722590defd45ff2
• https://git.kernel.org/stable/c/b2de2b4d4e007f9add46ea8dc06f781835e3ea9f
• https://git.kernel.org/stable/c/3ba95cc671c025d0d2a1c7d5e2930f0ff0980cf4
• https://git.kernel.org/stable/c/93827a0a36396f2fd6368a54a020f420c8916e9b