* [CVE-2026-98712][MODERATE 7.0] KVM: arm64: vgic: Take a refcount on IRQs referenced by last_lr_irq
@ 2026-10-24 17:01 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 17:01 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98712
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: KVM: arm64: vgic: Take a refcount on IRQs referenced by last_lr_irq
Commit: 8b25393d16a5ca8df907bd7ee1ff2e9d85678b3c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8b25393d16a5ca8df907bd7ee1ff2e9d85678b3c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98712
Analysis date: Sat, 24 Oct 2026 13:01:37 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A missing reference on `last_lr_irq` permits concurrent LPI deletion to leave an active stale IRQ pointer that host VGIC pruning later consumes.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98712 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98712
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-2026-98712 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98712 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=6 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'A race in KVM arm64 VGIC can leave last_lr_irq holding an LPI pointer lacking a lifetime reference while concurrent LPI unmapping deletes the IRQ. Later AP list pruning can access the stale pointer, establishing a host kernel use after free candidate with crash impact and a plausible guest to host confidentiality or integrity risk, although the diff does not demonstrate an arbitrary write primitive. For the CVSS the PR:L value reflects that reliable triggering requires control of a VM or KVM execution context and the virtual LPI lifecycle rather than unauthenticated network access. AC:H reflects the need to race LR population against LPI unmapping. The issue is not directly network reachable, but a malicious guest able to drive VGIC LPI operations may race host vCPU execution. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7.8 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because a specific evidence based protection or manual review veto was applied and FD false positive review allowed a downgrade. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and V33_ACTIVE_STATE_BOUNDARY_CANDIDATE and IMPORTANT_CANDIDATE_MANUAL_REVIEW and KP_ONLY_DOWNGRADE_VETO and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 6 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE DANGER VIRT SIMPLEFIX HARDWARE LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS V33_ACTIVE_STATE_BOUNDARY_CANDIDATE IMPORTANT_CANDIDATE_MANUAL_REVIEW KP_ONLY_DOWNGRADE_VETO DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 3.
* Conservative score: 4. Real-UAF floor 4 applied: 3 -> 4.
* Raw paranoid score: 5.
* Paranoid score: 5.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 real UAF: `last_lr_irq` retains an IRQ/LPI pointer without a reference, while concurrent LPI unmapping can delete that object.
* +1 plausible host-kernel crash: AP-list pruning later consumes the stale pointer.
* Paranoid +1 attacker-influenced lifetime manipulation: the supplied KVM attack model supports a VM/VMM actor driving virtual LPI lifecycle operations while vCPU LR processing runs.
* Paranoid +1 structured stale-object leverage: the stale IRQ is active VGIC state used during AP-list pruning and reclamation, not fixed transfer storage or merely diagnostic metadata.
* No race penalty: concurrency is required, but the evidence does not establish a one-shot or externally uncontrollable race.
* No controlled reclaim, attacker-shaped replacement, arbitrary write, callback control, disclosure, or LPE is shown.
* No extra availability point; it would duplicate the same crash.
* No strong guest-to-host corrupt bonus: host UAF is proven, but a useful guest-directed host-memory primitive is not.
3. Reachability analysis
A local below-host-admin VMM actor with permitted `/dev/kvm` access can control VM execution and virtual interrupt lifecycle; host UID 0 is not inherently required. Pure guest-only completion is less certain because the supplied source does not show whether every unmap/reclamation stage is guest-driven or requires VMM involvement. This is therefore strongest as a local VMM or potentially compound guest-plus-VMM trigger. No namespace-capability path, special hardware prerequisite beyond arm64 virtualization, or prior host-admin configuration is established.
4. Primitive and severity reading
This is an active structured host-kernel UAF: LR population publishes `last_lr_irq` without retaining the IRQ, concurrent unmapping may destroy it, and later privileged VGIC pruning consumes the stale reference. The fix adds a reference at publication and releases it during pruning.
The shown effect is stale host-state access with plausible host crash. Controlled reuse, host memory read/write, and guest escape remain unproven. Nevertheless, the concrete active-state lifetime corruption, later privileged consumer, and credible VM/host trust boundary satisfy an Important-candidate review posture. Auto-downgrade is unsafe until guest-only reachability and post-reuse behavior are resolved.
5. One-sentence report phrase
A missing reference on `last_lr_irq` permits concurrent LPI deletion to leave an active stale IRQ pointer that host VGIC pruning later consumes.
6. Manual review advice
MANUAL CHECK REQUIRED
Confirm whether guest-controlled ITS/LPI operations alone can complete the race and inspect the stale pruning operations for host-memory effects beyond an immediate crash.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: KVM: arm64: vgic: Take a refcount on IRQs referenced by last_lr_irq
Commit: 8b25393d16a5ca8df907bd7ee1ff2e9d85678b3c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8b25393d16a5ca8df907bd7ee1ff2e9d85678b3c
Commit description:
Referencing the last interrupt inserted in an LR is rather fragile, as
this interrupt can vanish if a concurrently unmapped LPI.
Solve this by bumping up the refcount on the interrupt when populating
last_lr_irq, and drop it at vgic_prune_ap_list() time, when LPIs are
being reclaimed.
Fixes: 6da5e53 ("KVM: arm64: vgic: Pick EOIcount deactivations from AP-list tail")
Reported-by: Yuchao Zhang <[email protected]>
Reviewed-by: Fuad Tabba <[email protected]>
Tested-by: Fuad Tabba <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>
Cc: [email protected]
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Oliver Upton <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
arch/arm64/kvm/vgic/vgic.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=8b25393d16a5ca8df907bd7ee1ff2e9d85678b3c
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98712 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98712
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:L/I:L/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
The Best / paranoid CVSS score: 7.8
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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