Linux Kernel up to 6.18.9 KVM kvm_arch_irq_bypass_del_producer null pointer dereference

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5.0$0-$5k0.00

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.18.9. It has been declared as critical. The affected element is the function kvm_arch_irq_bypass_del_producer of the component KVM. The manipulation results in null pointer dereference. This vulnerability is cataloged as CVE-2026-23198. There is no exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, was found in Linux Kernel up to 6.18.9. Affected is the function kvm_arch_irq_bypass_del_producer of the component KVM. The manipulation with an unknown input leads to a null pointer dereference vulnerability. CWE is classifying the issue as CWE-476. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. This is going to have an impact on availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: KVM: Don't clobber irqfd routing type when deassigning irqfd When deassigning a KVM_IRQFD, don't clobber the irqfd's copy of the IRQ's routing entry as doing so breaks kvm_arch_irq_bypass_del_producer() on x86 and arm64, which explicitly look for KVM_IRQ_ROUTING_MSI. Instead, to handle a concurrent routing update, verify that the irqfd is still active before consuming the routing information. As evidenced by the x86 and arm64 bugs, and another bug in kvm_arch_update_irqfd_routing() (see below), clobbering the entry type without notifying arch code is surprising and error prone. As a bonus, checking that the irqfd is active provides a convenient location for documenting _why_ KVM must not consume the routing entry for an irqfd that is in the process of being deassigned: once the irqfd is deleted from the list (which happens *before* the eventfd is detached), it will no longer receive updates via kvm_irq_routing_update(), and so KVM could deliver an event using stale routing information (relative to KVM_SET_GSI_ROUTING returning to userspace). As an even better bonus, explicitly checking for the irqfd being active fixes a similar bug to the one the clobbering is trying to prevent: if an irqfd is deactivated, and then its routing is changed, kvm_irq_routing_update() won't invoke kvm_arch_update_irqfd_routing() (because the irqfd isn't in the list). And so if the irqfd is in bypass mode, IRQs will continue to be posted using the old routing information. As for kvm_arch_irq_bypass_del_producer(), clobbering the routing type results in KVM incorrectly keeping the IRQ in bypass mode, which is especially problematic on AMD as KVM tracks IRQs that are being posted to a vCPU in a list whose lifetime is tied to the irqfd. Without the help of KASAN to detect use-after-free, the most common sympton on AMD is a NULL pointer deref in amd_iommu_update_ga() due to the memory for irqfd structure being re-allocated and zeroed, resulting in irqfd->irq_bypass_data being NULL when read by avic_update_iommu_vcpu_affinity(): BUG: kernel NULL pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 40cf2b9067 P4D 40cf2b9067 PUD 408362a067 PMD 0 Oops: Oops: 0000 [#1] SMP CPU: 6 UID: 0 PID: 40383 Comm: vfio_irq_test Tainted: G U W O 6.19.0-smp--5dddc257e6b2-irqfd #31 NONE Tainted: [U]=USER, [W]=WARN, [O]=OOT_MODULE Hardware name: Google, Inc. Arcadia_IT_80/Arcadia_IT_80, BIOS 34.78.2-0 09/05/2025 RIP: 0010:amd_iommu_update_ga+0x19/0xe0 Call Trace: <TASK> avic_update_iommu_vcpu_affinity+0x3d/0x90 [kvm_amd] __avic_vcpu_load+0xf4/0x130 [kvm_amd] kvm_arch_vcpu_load+0x89/0x210 [kvm] vcpu_load+0x30/0x40 [kvm] kvm_arch_vcpu_ioctl_run+0x45/0x620 [kvm] kvm_vcpu_ioctl+0x571/0x6a0 [kvm] __se_sys_ioctl+0x6d/0xb0 do_syscall_64+0x6f/0x9d0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x46893b </TASK> ---[ end trace 0000000000000000 ]--- If AVIC is inhibited when the irfd is deassigned, the bug will manifest as list corruption, e.g. on the next irqfd assignment. list_add corruption. next->prev should be prev (ffff8d474d5cd588), but was 0000000000000000. (next=ffff8d8658f86530). ------------[ cut here ]------------ kernel BUG at lib/list_debug.c:31! Oops: invalid opcode: 0000 [#1] SMP CPU: 128 UID: 0 PID: 80818 Comm: vfio_irq_test Tainted: G U W O 6.19.0-smp--f19dc4d680ba-irqfd #28 NONE Tainted: [U]=USER, [W]=WARN, [O]=OOT_MODULE Hardware name: Google, Inc. Arcadia_IT_80/Arcadia_IT_80, BIOS 34.78.2-0 09/05/2025 RIP: 0010:__list_add_valid_or_report+0x97/0xc0 Call Trace: <TASK> avic_pi_update_irte+0x28e/0x2b0 [kvm_amd] kvm_pi_update_irte+0xbf/0x190 [kvm] kvm_arch_irq_bypass_add_producer+0x72/0x90 [kvm] irq_bypass_register_consumer+0xcd/0x170 [irqbypa ---truncated---

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2026-23198 since 01/13/2026. The exploitability is told to be difficult. There are known technical details, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 299082 (Linux Distros Unpatched Vulnerability : CVE-2026-23198), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 5.10.250, 5.15.200, 6.1.163, 6.6.124, 6.12.70 or 6.18.10 eliminates this vulnerability. Applying the patch 959a063e7f12524bc1871ad1f519787967bbcd45/2284bc168b148a17b5ca3b37b3d95c411f18a08d/6d14ba1e144e796b5fc81044f08cfba9024ca195/b61f9b2fcf181451d0a319889478cc53c001123e/ff48c9312d042bfbe826ca675e98acc6c623211c/4385b2f2843549bfb932e0dcf76bf4b065543a3c/b4d37cdb77a0015f51fee083598fa227cc07aaf1 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (299082) and CERT Bund (WID-SEC-2026-0421). Once again VulDB remains the best source for vulnerability data.

Affected

  • Google Container-Optimized OS
  • Debian Linux
  • Google Cloud Platform
  • Amazon Linux 2
  • Red Hat Enterprise Linux
  • Ubuntu Linux
  • SUSE Linux
  • Oracle Linux
  • SUSE openSUSE
  • RESF Rocky Linux
  • Open Source Linux Kernel
  • IBM QRadar SIEM

Productinfo

Type

Vendor

Name

Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.1
VulDB Meta Temp Score: 5.0

VulDB Base Score: 4.8
VulDB Temp Score: 4.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 5.5
NVD Vector: 🔒

CVSSv2info

AVACAuCIA
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💳💳💳💳💳💳
💳💳💳💳💳💳
VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Null pointer dereference
CWE: CWE-476 / CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 299082
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2026-23198

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 5.10.250/5.15.200/6.1.163/6.6.124/6.12.70/6.18.10
Patch: 959a063e7f12524bc1871ad1f519787967bbcd45/2284bc168b148a17b5ca3b37b3d95c411f18a08d/6d14ba1e144e796b5fc81044f08cfba9024ca195/b61f9b2fcf181451d0a319889478cc53c001123e/ff48c9312d042bfbe826ca675e98acc6c623211c/4385b2f2843549bfb932e0dcf76bf4b065543a3c/b4d37cdb77a0015f51fee083598fa227cc07aaf1

Timelineinfo

01/13/2026 CVE reserved
02/14/2026 +32 days Advisory disclosed
02/14/2026 +0 days VulDB entry created
05/05/2026 +80 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-23198 (🔒)
GCVE (CVE): GCVE-0-2026-23198
GCVE (VulDB): GCVE-100-346044
CERT Bund: WID-SEC-2026-0421 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 02/14/2026 18:05
Updated: 05/05/2026 22:13
Changes: 02/14/2026 18:05 (59), 02/14/2026 19:43 (1), 02/15/2026 16:32 (2), 02/19/2026 14:44 (1), 03/19/2026 18:26 (11), 05/05/2026 22:13 (7)
Complete: 🔍
Cache ID: 216::103

Once again VulDB remains the best source for vulnerability data.

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