Linux Kernel up to 6.12.94/6.18.37/7.1.2 Ioeventfd virt/kvm/eventfd.c ioeventfd_write val null pointer dereference

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6.6$0-$5k0.00

Summaryinfo

A vulnerability, which was classified as critical, has been found in Linux Kernel up to 6.12.94/6.18.37/7.1.2. Impacted is the function ioeventfd_write of the file virt/kvm/eventfd.c of the component Ioeventfd. This manipulation of the argument val causes null pointer dereference. This vulnerability appears as CVE-2026-63806. The attack may be initiated remotely. There is no available exploit. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability classified as critical was found in Linux Kernel up to 6.12.94/6.18.37/7.1.2. Affected by this vulnerability is the function ioeventfd_write of the file virt/kvm/eventfd.c of the component Ioeventfd. The manipulation of the argument val with an unknown input leads to a null pointer dereference vulnerability. The CWE definition for the vulnerability is 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. As an impact it is known to affect availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: KVM: Replace guest-triggerable BUG_ON() in ioeventfd datamatch with get_unaligned() Drop a BUG_ON() that has been reachable since it was first added, way back in 2009, and instead use get_unaligned() to perform potentially-unaligned accesses. For a given store, KVM x86's emulator tracks the entire value in the destination operand, x86_emulate_ctxt.dst. If the destination is memory, and the target splits multiple pages and/or is emulated MMIO, then KVM handles each fragment independently. E.g. on a page split starting at page offset 0xffc, KVM writes 4 bytes to the first page, then the remaining bytes to the second page, using ctxt->dst as the source for both (with appropriate offsets). If the destination splits a page *and* hits emulated MMIO on the second page, then KVM will complete the write to the first page, then emulate the MMIO access to the second page. If there is a datamatch-enabled ioeventfd at offset 0 of the second page, then KVM will process the remainder of the store as a potential ioeventfd signal. Putting it all together, if the guest emits a store that splits a page starting at page offset N, and the second page has a datamatch-enabled ioeventfd at offset 0, then KVM will check for datamatch using &dst.valptr[N] as the source. Due to dst (and thus dst.valptr) being 32-byte aligned, if N is not aligned to @len, the BUG_ON() fires. E.g. with a 16-byte store at page offset 0xffc, to an ioeventfd of len 8, all initial checks in ioeventfd_in_range() will succeed, and the BUG_ON() fires due to @val being 4-byte aligned, but not 8-byte aligned. ------------[ cut here ]------------ kernel BUG at arch/x86/kvm/../../../virt/kvm/eventfd.c:783! Oops: invalid opcode: 0000 [#1] SMP CPU: 0 UID: 1000 PID: 615 Comm: repro Not tainted 7.1.0-rc2-ff238429d1ea #365 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:ioeventfd_write+0x6c/0x70 [kvm] Call Trace: <TASK> __kvm_io_bus_write+0x85/0xb0 [kvm] kvm_io_bus_write+0x53/0x80 [kvm] vcpu_mmio_write+0x66/0xf0 [kvm] emulator_read_write_onepage+0x12a/0x540 [kvm] emulator_read_write+0x109/0x2b0 [kvm] x86_emulate_insn+0x4f8/0xfb0 [kvm] x86_emulate_instruction+0x181/0x790 [kvm] kvm_mmu_page_fault+0x313/0x630 [kvm] vmx_handle_exit+0x18a/0x590 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xc81/0x1c90 [kvm] kvm_vcpu_ioctl+0x2d5/0x970 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0xb7/0x890 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f19c931a9bf </TASK> Modules linked in: kvm_intel kvm irqbypass ---[ end trace 0000000000000000 ]--- In a perfect world, the fix would be to simply delete the BUG_ON(), as KVM x86 doesn't perform alignment checks on "normal" memory accesses at CPL0. Sadly, C99 ruins all the fun; while the x86 architecture plays nice, dereferencing an unaligned pointer directly is undefined behavior in C, e.g. triggers splats when running with CONFIG_UBSAN_ALIGNMENT=y.

It is possible to read the advisory at git.kernel.org. This vulnerability is known as CVE-2026-63806 since 07/19/2026. The exploitation appears to be easy. The attack can be launched remotely. Technical details of the vulnerability are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 335327 (SUSE SLES15: cluster-md-kmp-default / dlm-kmp-default / gfs2-kmp-default / etc (SUSE-SU-2026:3602-1)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.12.95, 6.18.38, 7.1.3 or 7.2-rc1 eliminates this vulnerability.

The vulnerability is also documented in the databases at CNNVD (CNNVD-2026-98701678), Tenable (335327), EUVD (EUVD-2026-45472) and CERT Bund (WID-SEC-2026-2403). Be aware that VulDB is the high quality source for vulnerability data.

Affected

  • Debian Linux
  • Red Hat Enterprise Linux
  • RESF Rocky Linux
  • SUSE openSUSE
  • Ubuntu Linux
  • Oracle Linux
  • Open Source Linux Kernel

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.8
VulDB Meta Temp Score: 6.6

VulDB Base Score: 6.5
VulDB Temp Score: 6.2
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 7.1
CNA Vector (Linux): 🔒

CVSSv2info

AVACAuCIA
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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: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 335327
Nessus Name: SUSE SLES15: cluster-md-kmp-default / dlm-kmp-default / gfs2-kmp-default / etc (SUSE-SU-2026:3602-1)

Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.12.95/6.18.38/7.1.3/7.2-rc1

Timelineinfo

07/19/2026 Advisory disclosed
07/19/2026 +0 days CVE reserved
07/19/2026 +0 days VulDB entry created
08/17/2026 +29 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-63806 (🔒)
GCVE (CVE): GCVE-0-2026-63806
GCVE (VulDB): GCVE-100-380143
EUVD: 🔒
CERT Bund: WID-SEC-2026-2403 - Linux Kernel: Mehrere Schwachstellen erm&ouml;glichen nicht spezifizierten Angriff
CNNVD: CNNVD-2026-98701678 - Linux kernel 安全漏洞

Entryinfo

Created: 07/19/2026 16:00
Updated: 08/17/2026 07:57
Changes: 07/19/2026 16:00 (57), 07/19/2026 17:04 (1), 07/20/2026 23:11 (6), 08/06/2026 07:45 (10), 08/14/2026 18:49 (2), 08/17/2026 07:57 (11)
Complete: 🔍
Cache ID: 216::103

Be aware that VulDB is the high quality source for vulnerability data.

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