* [CVE-2026-89727][MODERATE 7.0] KVM: arm64: GICv2: Don't WARN on out-of-range GICV_DIR INTID
@ 2026-09-12 2:17 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-12 2:17 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89727
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: KVM: arm64: GICv2: Don't WARN on out-of-range GICV_DIR INTID
Commit: 78b95c571d021391153a5ac7981e9e4d5cc856a3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=78b95c571d021391153a5ac7981e9e4d5cc856a3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89727
Analysis date: Fri, 11 Sep 2026 22:17:43 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89727 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89727
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-2026-89727 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89727 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H';CWE-617;CWE-703;CWE-754;BEST CVSS score: '6.5';DESCR 'A guest controlled out-of-range INTID written to GICV_DIR can make vgic_get_vcpu_irq return NULL in the KVM arm64 GICv2 deactivate path. The old code treated this as an impossible condition and reached WARN_ON_ONCE, which can panic the host when panic_on_warn is enabled. For the CVSS the PR:L is chosen because the attacker needs control over a guest VM or guest code path, but does not need administrative privileges on the host. The issue is not network reachable and is triggered through the virtual interrupt controller interface rather than packet traffic. Impact is denial of service against the host via kernel panic. No confidentiality or integrity impact is assigned because the patch shows a reachable warning and NULL lookup handling issue, not a UAF, OOB access, or write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5) SKIP CVE-2026-89727 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE OOB VIRT SIMPLEFIX HARDWARE LINUS KPANIC - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4. No floor or cap applied.
* Raw paranoid score: 5
* Paranoid score: 5. No floor or cap applied.
* Final recommended bucket: **Actionable Moderate**::
2. Signal breakdown
Conservative signals:
* +1 Reliable kernel crash / strong DoS. A guest supplied out of range GICV_DIR INTID can reach WARN_ON_ONCE, and hosts with panic_on_warn can panic.
* +1 Confirmed guest-to-host host DoS consequence. The supplied evidence explicitly states that guest behavior can panic the host under panic_on_warn.
* +1 Guest-controlled trigger. The guest can make the failed IRQ lookup happen at will by writing an out of range INTID with EOImode==1.
* +1 Below-host-admin reachability in the host security model. The attacker needs control of guest execution, not host administrative privileges.
Paranoid additional signal:
* +1 Paranoid operational weighting for virtualization-boundary DoS. The issue is still WARN-based rather than corruption, but the trigger crosses from guest behavior into host kernel fatal behavior on hardened panic_on_warn deployments.
Non-awarded signals:
* No RealUAF. The patch shows a NULL lookup and reachable WARN, not post-lifetime object use.
* No Class A primitive. No controlled reclaim, arbitrary write, callback control, or demonstrated guest-to-host memory corruption is established.
* No C/I impact. The evidence supports host DoS only.
* No remote network reachability. The trigger is via the virtual interrupt controller interface, not packet traffic.
* No race penalty. This is not a timing race.
* No extra availability point. The same host panic is already counted once.
* No KVM strong guest-to-host exploitation leverage. Guest-to-host host panic is established, but not a stronger host memory corruption or escape primitive.
3. Reachability analysis
The evaluated attacker is a malicious guest or code running inside a guest VM. The guest can write an out of range INTID to GICV_DIR when running with EOImode==1, which reaches vgic_v2_deactivate() in the host KVM arm64 GICv2 path.
Host administrator privilege is not required for the host-side security model once the attacker controls guest execution. However, the issue requires an existing KVM arm64 VM using GICv2 behavior and affects host fatality primarily when panic_on_warn is enabled. This is not namespace-scoped and no network path is established.
The trigger is not compound in the sense of needing host VMM lifecycle operations plus guest operations. The relevant malformed INTID is guest supplied, and the later host handling occurs inside KVM. No guest-controlled object free, zap, reclaim, or replacement is shown.
4. Primitive and severity interpretation
The exact primitive is a guest-reachable invalid state assertion: vgic_get_vcpu_irq() returns NULL for an out of range GICV_DIR INTID, and the old code treats this with WARN_ON_ONCE. On panic_on_warn systems, this becomes a host kernel panic.
This is Class C. It is demonstrated crash / DoS behavior without an independently useful corruption primitive. It is not an active structured UAF, fixed stale storage UAF, repeated release/refcount mutation, OOB access, or authorization bypass.
The demonstrated consequence is guest-to-host denial of service. The speculative consequence of stronger guest-to-host compromise is not supported by the patch. ImportantCandidate is NO because no Important-grade exploitation primitive is established. AutoDowngradeAllowed is NO because automatic closure would risk losing a confirmed virtualization-boundary host DoS that is directly guest-triggerable on panic_on_warn hosts, even though the issue is not a strong Important candidate.
Likely operational severity is Actionable Moderate: it is more important than an ordinary local WARN because the warning is guest-controlled and can panic hardened hosts, but it should not be treated as memory corruption or privilege escalation.
5. One-sentence report phrase
A guest controlled out of range GICV_DIR INTID in KVM arm64 GICv2 can trigger a host WARN_ON_ONCE and panic hosts running panic_on_warn, causing guest-to-host denial of service without evidence of UAF, memory corruption, or privilege escalation.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: confirmed guest-controlled host panic across a virtualization boundary should be reviewed manually, even though the primitive is WARN/DoS only and not memory corruption.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: KVM: arm64: GICv2: Don't WARN on out-of-range GICV_DIR INTID
Commit: 78b95c571d021391153a5ac7981e9e4d5cc856a3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=78b95c571d021391153a5ac7981e9e4d5cc856a3
Commit description:
vgic_v2_deactivate() passes the INTID a guest wrote to GICV_DIR straight
to vgic_get_vcpu_irq(), and treats a failed lookup as a "can't happen"
condition with WARN_ON_ONCE().
The guest can make it happen at will, though: for any INTID outside of
the implemented SGI, PPI and SPI ranges the lookup returns NULL, since
GICv2 has no LPIs. A guest running with EOImode==1 writing such an INTID
to GICV_DIR triggers the WARN, and panics hosts running with
panic_on_warn.
Drop the WARN and ignore failed lookups.
Fixes: 255de89 ("KVM: arm64: GICv2: Handle deactivation via GICV_DIR traps")
Cc: [email protected]
Suggested-by: Marc Zyngier <[email protected]>
Signed-off-by: Karl Mehltretter <[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-v2.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=78b95c571d021391153a5ac7981e9e4d5cc856a3
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89727 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89727
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: Not available
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
The Best / paranoid CVSS score: 6.5
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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