* [CVE-2026-98465][MODERATE 7.0] RISC-V: KVM: Serialize IMSIC attributes with vCPU migration [ Upstream
@ 2026-10-24 13:53 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 13:53 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98465
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: RISC-V: KVM: Serialize IMSIC attributes with vCPU migration [ Upstream
Commit: a29c5d2dd2ef9a8617a9a6d5585696d5f149cd98
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a29c5d2dd2ef9a8617a9a6d5585696d5f149cd98
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98465
Analysis date: Sat, 24 Oct 2026 09:53:46 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A KVM_RUN race can recycle an IMSIC VS-file while an attribute ioctl retains its old CPU/HGEI locator, causing a subsequent GET or SET to access another vCPU's live interrupt state.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98465 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98465
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-2026-98465 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98465 CHECK WITH IMPACT FROM ORIG NN NONE | AEGIS IMPACT MODERATE AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=DIFF TEMP_DISTANCE_MERGE=IMPORTANT->MODERATE_KPANIC;AEGIS=MODERATE;GAP=2 (final Legacy and Aegis differ; FINAL: MODERATE_KPANIC, Aegis: 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:L/I:L/A:H';CWE-362;CWE-367;CWE-667;CWE-863;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:C/C:L/I:L/A:L';BEST CVSS score: '7';DESCR 'A race between an IMSIC GET or SET device attribute ioctl and KVM_RUN can leave kvm_riscv_aia_imsic_rw_attr using a stale physical CPU and HGEI tuple after vCPU migration releases the VS file and another vCPU acquires it. The stale tuple permits an unauthorized read or write of the new owner interrupt file, creating a concrete cross vCPU and potentially cross VM confidentiality, integrity, and availability impact. The evidence does not indicate OOB access, UAF, arbitrary host memory access, or host code execution. For the CVSS the PR:L value is selected because triggering requires local KVM access and a VM or vCPU file descriptor. AC:H reflects the need to win the migration and HGEI reuse timing window. Scope is changed only when the recycled VS file belongs to a different VM or tenant. The base impact is limited because the primitive is confined to IMSIC interrupt state, while the paranoid score raises availability for plausible disruption of another guest interrupt delivery. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 6 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 LOW to MODERATE_KPANIC because the ActionableScore threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to IMPORTANT because the ActionableScore threshold rule was applied. final reconciliation stage IMPORTANT to MODERATE_KPANIC because the cross model evidence reconciliation rule was applied. 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_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 and INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 and TEMP_DISTANCE_MERGE. The independent weaker Aegis shadow evaluated CVSS 3.6 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE. Cross model aggregation changed the production result under an enabled evidence gated merge rule. 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 6) MAYBE LOCK DANGER VIRT SIMPLEFIX SKIP HARDWARE LINUS KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 TEMP_DISTANCE_MERGE - - checked
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ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=CONFIRMED
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 5.
* Conservative score: 5; no floor or cap applied.
* Raw paranoid score: 6.
* Paranoid score: 6; no floor or cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 strong active-state/ownership primitive: a stale physical-CPU/HGEI tuple directs IMSIC GET or SET to a VS-file that has been recycled to another vCPU.
* +1 local below-host-admin trigger: supplied evidence grounds access through local KVM device ioctls and VM/vCPU descriptors without host UID 0.
* +1 practical chain: concurrent KVM_RUN migration releases the file, another vCPU acquires it, and `imsic_vsfile_rw()` consumes the stale tuple.
* +1 confidentiality: GET can read the new owner's interrupt-file state.
* +1 integrity: SET can modify that protected active interrupt state.
* -1 hard timing: exploitation requires winning the migration and HGEI-reuse race.
* Paranoid +1 cross-boundary concern: allocation to a vCPU belonging to another VM is technically credible, but not conclusively established by the patch.
Not awarded: UAF/OOB or arbitrary host-memory access; controlled reclaim; host code execution; proven cross-VM access; separate crash/availability points; authorization-decision bypass. B5-R and B4-PENDING do not apply.
3. Reachability analysis
The relevant attacker is a local VMM process with `/dev/kvm` and the target VM/vCPU descriptors, not guest code acting alone. That process can invoke the IMSIC attribute ioctl while KVM_RUN executes, but HGEI reuse and migration timing make the race difficult. The evidence supports below-host-admin KVM access and does not require UID 0. It does not establish namespace-scoped capabilities or a guest-only trigger. RISC-V AIA/IMSIC hardware support is required, but the evidence does not justify a rare-hardware penalty.
4. Primitive and severity reading
This is not stale heap storage or a UAF. It is a stale active resource locator—CPU plus HGEI—consumed by a later privileged kernel operation after ownership has changed. GET/SET consequently reaches another vCPU's live interrupt file. That is a directed protected-state read/write and ownership violation, hence CLASS_A, though confined to IMSIC interrupt state.
Cross-vCPU access is shown; cross-VM isolation impact is credible but unresolved. No arbitrary host-memory primitive, LPE, or guaranteed host crash is shown. ImportantCandidate is YES because corrupted active ownership state is consumed and the VM trust boundary remains specifically credible but unknown. Auto-downgrade is unsafe pending allocation-scope and cross-VM review.
5. One-sentence report phrase
A KVM_RUN race can recycle an IMSIC VS-file while an attribute ioctl retains its old CPU/HGEI locator, causing a subsequent GET or SET to access another vCPU's live interrupt state.
6. Manual review advice
MANUAL CHECK REQUIRED
Confirm whether HGEI recycling can select a vCPU from another VM/security principal and characterize the resulting interrupt-state read, write, and availability effects.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: RISC-V: KVM: Serialize IMSIC attributes with vCPU migration [ Upstream
Commit: a29c5d2dd2ef9a8617a9a6d5585696d5f149cd98
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a29c5d2dd2ef9a8617a9a6d5585696d5f149cd98
Changed files:
arch/riscv/kvm/aia_imsic.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=a29c5d2dd2ef9a8617a9a6d5585696d5f149cd98
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98465 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98465
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:C/C:L/I:L/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:C/C:L/I:L/A:H
The Best / paranoid CVSS score: 7
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: 5
Paranoid ActionableScore: 6
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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