[CVE-2026-72284][MODERATE 7.0] KVM: x86: Ignore pending PV EOI if the vCPU has since disabled PV EOIs

[CVE-2026-72284][MODERATE 7.0] KVM: x86: Ignore pending PV EOI if the vCPU has since disabled PV EOIs

[AL-KERNEL]

CVE: CVE-2026-72284
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: KVM: x86: Ignore pending PV EOI if the vCPU has since disabled PV EOIs
Commit: 038b9ce6fafda1babd1e33d52cbc6039747a6d87
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=038b9ce6fafda1babd1e33d52cbc6039747a6d87
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72284
Analysis date: Sat, 15 Aug 2026 12:04:56 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A stale pending PV EOI request in KVM x86 can remain after the vCPU disables PV EOI, allowing a KVM guest context to trigger a host kernel BUG and cause denial of service.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-72284 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72284

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-72284	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H';CWE-617;CWE-362;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.6';DESCR 'KVM x86 can reach a host kernel BUG when an internal pending PV EOI request remains set after the vCPU has disabled PV EOI. The failure path depends on pv_eoi_test_and_clr_pending returning early after a guest memory read failure and the vCPU disabling PV EOI before the pending request is serviced. This causes kvm_lapic_sync_from_vapic to hit an assertion and crash the host kernel. For the CVSS the PR:L is used because the attacker needs the ability to run or control a KVM guest or vCPU, but does not need full host administrator privileges. The issue is not directly network reachable. Impact is denial of service of the host via kernel crash, with no concrete evidence of information disclosure or privilege escalation from this patch.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	DANGER VIRT INIT HARDWARE KPANIC 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1. A user or tenant able to run or control a KVM vCPU can potentially trigger the path without host root.
* Reliable kernel crash / strong DoS: +1. The commit shows a kernel BUG / invalid opcode in KVM host code.
* Cross-boundary isolation impact: +1. A guest-controlled condition can crash the host kernel and affect other workloads.
* Availability impact realistic: +1. The failure is host-wide DoS, not only a guest-local failure.
* Broadly deployed exposure: +1 in paranoid scoring. KVM is common in virtualization environments.
* Hard or timing-dependent condition: -1. The trigger requires a pending PV EOI request, guest memory read failure, and PV EOI disable timing.

No memory corruption, UAF, OOB write, arbitrary write, information leak, or privilege-escalation primitive is shown by the patch.

## 3. Reachability analysis

The bug is reachable through KVM execution paths by a local user, VM manager, or guest tenant that can run a vCPU and influence PV EOI state. It is not directly network reachable. Namespaces do not by themselves expose the bug, but practical deployments may delegate KVM access through `/dev/kvm` or a virtualization stack, so PR:L is more appropriate than PR:H. The path is relevant on KVM hosts using PV EOI support, but exploitation depends on a specific stale pending request state and read-failure timing.

## 4. Severity interpretation

This behaves like an actionable Moderate KVM guest-to-host DoS rather than an Important memory-corruption issue. The realistic impact is host kernel crash. The theoretical risk does not extend to LPE or confidentiality/integrity compromise based on the provided patch, because the fix only replaces a reachable `BUG_ON()` assertion with state revalidation and clearing of the pending bit.

## 5. One-sentence report phrase

A stale pending PV EOI request in KVM x86 can remain after the vCPU disables PV EOI, allowing a KVM guest context to trigger a host kernel BUG and cause denial of service.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. This crosses the KVM guest-to-host boundary and can crash the host kernel, even though the visible primitive is assertion-triggered DoS rather than memory corruption.

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: KVM: x86: Ignore pending PV EOI if the vCPU has since disabled PV EOIs
Commit: 038b9ce6fafda1babd1e33d52cbc6039747a6d87
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=038b9ce6fafda1babd1e33d52cbc6039747a6d87

Commit description:

Ignore KVM's internal "service pending PV EOI" request if the vCPU has
disabled PV EOIs since the request was made.  Asserting that PV EOIs are
enabled can fail if reading guest memory in pv_eoi_get_user() fails, i.e.
if pv_eoi_test_and_clr_pending() bails early, *and* the vCPU also disables
PV EOIs.

  kernel BUG at arch/x86/kvm/lapic.c:3338!
  Oops: invalid opcode: 0000 [#1] SMP
  CPU: 4 UID: 1000 PID: 890 Comm: pv_eoi_test Not tainted 7.0.0-d585aa5894d8-vm #337 PREEMPT
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  RIP: 0010:kvm_lapic_sync_from_vapic+0x12b/0x140 [kvm]
  Call Trace:
   <TASK>
   kvm_arch_vcpu_ioctl_run+0x1075/0x1c30 [kvm]
   kvm_vcpu_ioctl+0x2d5/0x980 [kvm]
   __x64_sys_ioctl+0x8a/0xd0
   do_syscall_64+0xb5/0xb40
   entry_SYSCALL_64_after_hwframe+0x4b/0x53
   </TASK>
  Modules linked in: kvm_intel kvm irqbypass
  ---[ end trace 0000000000000000 ]---

Fixes: ae7a2a3 ("KVM: host side for eoi optimization")
Cc: stable@vger.kernel.org
Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://patch.msgid.link/20260624220516.3033391-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/x86/kvm/lapic.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=038b9ce6fafda1babd1e33d52cbc6039747a6d87

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-72284 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72284

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.6

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 4
  Paranoid ActionableScore: 5

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).