Linux Kernel up to 6.17.1 KVM complete_emulated_io permission

CVSS Meta Temp Score
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CTI Interest Score
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7.6$0-$5k0.00

Summaryinfo

A vulnerability classified as critical has been found in Linux Kernel up to 6.17.1. This affects the function complete_emulated_io of the component KVM. This manipulation causes permission. This vulnerability is tracked as CVE-2025-40026. No exploit exists. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.17.1. It has been declared as critical. Affected by this vulnerability is the function complete_emulated_io of the component KVM. The manipulation with an unknown input leads to a permission vulnerability. The CWE definition for the vulnerability is CWE-275. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Don't (re)check L1 intercepts when completing userspace I/O When completing emulation of instruction that generated a userspace exit for I/O, don't recheck L1 intercepts as KVM has already finished that phase of instruction execution, i.e. has already committed to allowing L2 to perform I/O. If L1 (or host userspace) modifies the I/O permission bitmaps during the exit to userspace, KVM will treat the access as being intercepted despite already having emulated the I/O access. Pivot on EMULTYPE_NO_DECODE to detect that KVM is completing emulation. Of the three users of EMULTYPE_NO_DECODE, only complete_emulated_io() (the intended "recipient") can reach the code in question. gp_interception()'s use is mutually exclusive with is_guest_mode(), and complete_emulated_insn_gp() unconditionally pairs EMULTYPE_NO_DECODE with EMULTYPE_SKIP. The bad behavior was detected by a syzkaller program that toggles port I/O interception during the userspace I/O exit, ultimately resulting in a WARN on vcpu->arch.pio.count being non-zero due to KVM no completing emulation of the I/O instruction. WARNING: CPU: 23 PID: 1083 at arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm] Modules linked in: kvm_intel kvm irqbypass CPU: 23 UID: 1000 PID: 1083 Comm: repro Not tainted 6.16.0-rc5-c1610d2d66b1-next-vm #74 NONE Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm] PKRU: 55555554 Call Trace: <TASK> kvm_fast_pio+0xd6/0x1d0 [kvm] vmx_handle_exit+0x149/0x610 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm] kvm_vcpu_ioctl+0x244/0x8c0 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0x5d/0xc60 entry_SYSCALL_64_after_hwframe+0x4b/0x53 </TASK>

The advisory is shared at git.kernel.org. This vulnerability is known as CVE-2025-40026 since 04/16/2025. The exploitation appears to be easy. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 02/27/2026). MITRE ATT&CK project uses the attack technique T1222 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 271897 (Linux Distros Unpatched Vulnerability : CVE-2025-40026), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 5.15.195, 6.1.157, 6.6.111, 6.12.52, 6.16.12, 6.17.2 or 6.18-rc1 eliminates this vulnerability. Applying the patch e0ce3ed1048a47986d15aef1a98ebda25560d257/ba35a5d775799ce5ad60230be97336f2fefd518e/3d3abf3f7e8b1abb082070a343de82d7efc80523/e7177c7e32cb806f348387b7f4faafd4a5b32054/3a062a5c55adc5507600b9ae6d911e247e2f1d6e/7366830642505683bbe905a2ba5d18d6e4b512b8/e750f85391286a4c8100275516973324b621a269 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 (271897) and CERT Bund (WID-SEC-2025-2430). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

  • Google Container-Optimized OS
  • Debian Linux
  • Amazon Linux 2
  • Ubuntu Linux
  • SUSE Linux
  • Oracle Linux
  • SUSE openSUSE
  • NetApp ActiveIQ Unified Manager
  • Open Source Linux Kernel
  • Microsoft Azure

Productinfo

Type

Vendor

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Version

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Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 8.0
VulDB Meta Temp Score: 7.6

VulDB Base Score: 8.0
VulDB Temp Score: 7.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

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

Exploitinginfo

Class: Permission
CWE: CWE-275 / CWE-266
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 271897
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2025-40026

Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 5.15.195/6.1.157/6.6.111/6.12.52/6.16.12/6.17.2/6.18-rc1
Patch: e0ce3ed1048a47986d15aef1a98ebda25560d257/ba35a5d775799ce5ad60230be97336f2fefd518e/3d3abf3f7e8b1abb082070a343de82d7efc80523/e7177c7e32cb806f348387b7f4faafd4a5b32054/3a062a5c55adc5507600b9ae6d911e247e2f1d6e/7366830642505683bbe905a2ba5d18d6e4b512b8/e750f85391286a4c8100275516973324b621a269

Timelineinfo

04/16/2025 CVE reserved
10/28/2025 +195 days Advisory disclosed
10/28/2025 +0 days VulDB entry created
02/27/2026 +122 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-40026 (🔒)
GCVE (CVE): GCVE-0-2025-40026
GCVE (VulDB): GCVE-100-330217
CERT Bund: WID-SEC-2025-2430 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 10/28/2025 11:22
Updated: 02/27/2026 21:05
Changes: 10/28/2025 11:22 (59), 10/28/2025 11:34 (1), 10/28/2025 15:43 (7), 10/29/2025 10:49 (2), 12/03/2025 14:44 (1), 12/22/2025 02:00 (1), 02/12/2026 14:22 (1), 02/27/2026 21:05 (1)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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