Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Don't (re)check L1...
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:
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
Impact
CVE-2025-40026 has a CVSS score of 7.9 (High). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2025-40026? CVE-2025-40026 is a high-severity security vulnerability. No fixed version is listed yet.
- How severe is CVE-2025-40026? CVE-2025-40026 has a CVSS score of 7.9 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Is there a fix for CVE-2025-40026? No fixed version is listed for CVE-2025-40026 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2025-40026 exploitable, and should I be worried? Whether CVE-2025-40026 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-40026 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.