* [CVE-2026-90121][MODERATE REGULAR] irqchip/gic-v5: Clear per-CPU IRS data on teardown [ Upstream
@ 2026-09-18 4:17 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-18 4:17 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90121
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: irqchip/gic-v5: Clear per-CPU IRS data on teardown [ Upstream
Commit: 54937af6f4a0d44c2852a203d457902f3264c906
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=54937af6f4a0d44c2852a203d457902f3264c906
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90121
Analysis date: Fri, 18 Sep 2026 00:17:32 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90121 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90121
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 REGULAR
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-2026-90121 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90121 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:H/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-672;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'GICv5 IRS affinity setup can publish irs_data through per CPU state before the remaining initialization has completed. If initialization later fails or the IRS is removed, the object can be freed while per_cpu_irs_data still references it and cpu_iaffid remains valid. A later consumer of this state may dereference freed kernel memory, causing at least a kernel crash or broken interrupt handling. In a worst case, reuse of the freed allocation could turn the stale pointer into a memory corruption primitive with possible confidentiality, integrity, and privilege escalation impact. This stronger impact is plausible for manual review but is not proven by the provided code because the later dereference and control over heap reuse have not been demonstrated. For the CVSS the PR:H reflects that IRS initialization and teardown are controlled by kernel boot, firmware, ACPI, or privileged platform management rather than an ordinary local user. The issue is not network reachable. AC:H reflects the required initialization failure or teardown sequence and a later access through the stale per CPU association.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) SKIP CVE-2026-90121 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE INIT ERRORPATH UAF HARDWARE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +2 Real UAF or lifetime violation. `irs_data` is published in `per_cpu_irs_data`, subsequently freed, and the exact stale per-CPU association remains available to later consumers.
* +1 Realistic kernel crash or strong DoS. A later IRQ affinity or IRS operation can dereference the freed structured object, plausibly causing an Oops or disrupting interrupt handling.
* No privilege penalty. The path is part of boot-time IRS initialization and teardown, but the supplied evidence does not establish who can induce the failure or teardown. Unknown privilege is not treated as host-admin privilege.
* No hardware penalty. GICv5 IRS hardware is required, but the evidence does not establish that it is sufficiently rare to justify a physical or rare-hardware deduction.
* No timing penalty. This is an ordered publication, initialization-failure, and cleanup defect rather than a demonstrated hard race.
* Controlled reclaim, attacker-shaped replacement data, arbitrary read/write, callback control, disclosure, and privilege escalation are not demonstrated.
* Structured stale-object leverage is not awarded because no later field-consuming path or attacker influence over reclaimed contents is shown.
* The `kfree(irs_data)` operation can end the object lifetime, and the exact pointer survives in per-CPU storage. However, no concrete second `put`, `free`, or refcount mutation is shown. The repeated-release bonus is therefore not awarded.
* Paranoid repeated-refcount leverage is withheld because no second lifetime mutation exists.
* FLOOR 5 is not applied because there is no repeated release, controlled reuse, or meaningful demonstrated post-free processing beyond a plausible stale dereference.
* No additional Availability point is awarded because it would duplicate the same potential crash.
* The supplied paranoid CVSS confidentiality and integrity values do not establish corresponding ActionableScore signals.
3. Reachability analysis
The vulnerable sequence occurs during GICv5 IRS initialization failure or normal IRS removal. These are global irqchip operations driven by kernel initialization, device tree or ACPI discovery, and platform teardown. No ordinary user, namespace capability, network input, or runtime userspace control interface is shown.
Below-host-admin reachability is not established, but neither is a complete malicious trigger requiring host-admin control. `HostAdminRequired` is therefore UNKNOWN. The operation is not user-namespace or network-namespace scoped. A platform implementing GICv5 IRS is required, but no evidence supports treating that hardware as rare for scoring. There is no race requirement. The faulty state follows deterministically once initialization fails after affinity publication.
4. Primitive and severity interpretation
The primitive is a dangling per-CPU pointer to a freed `struct gicv5_irs_chip_data`, accompanied by a stale valid IAFFID indication. This is an active structured kernel object rather than a simple scalar bookkeeping error, but the supplied patch does not show which fields a later consumer reads or modifies.
The free occurs in initialization error handling or IRS teardown. The stale association remains outside the freed object and can escape cleanup into later per-CPU use. This supports CLASS_B and `RealUAF=YES`.
There is no concrete repeated lifetime operation. The first `kfree()` ends the object lifetime, but the patch does not show a second `kfree()`, refcount decrement, or other lifetime mutation through the stale pointer. This is therefore closer to an ordinary stale dereference than repeated-lifetime corruption.
The demonstrated root cause supports potential crash or invalid interrupt handling. Controlled reclaim, useful post-free field consumption, and a practical privilege-escalation mechanism remain unestablished. Consequently, this is not an Important candidate on the supplied evidence. Automatic downgrade remains allowed because the UAF is constrained to initialization or teardown, meaningful exploitation leverage is not demonstrated, and no repeated lifetime mutation or security-boundary primitive remains unresolved.
5. One-sentence report phrase
GICv5 IRS initialization failure or teardown can leave a per-CPU pointer referencing freed IRS state, allowing a later consumer to dereference stale kernel memory and potentially crash the system or disrupt interrupt handling.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Review all readers of `per_cpu_irs_data` to determine whether they can execute after failed initialization or removal and whether they consume pointers, indices, mappings, or other fields that remain useful after allocator reuse.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: irqchip/gic-v5: Clear per-CPU IRS data on teardown [ Upstream
Commit: 54937af6f4a0d44c2852a203d457902f3264c906
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=54937af6f4a0d44c2852a203d457902f3264c906
Changed files:
drivers/irqchip/irq-gic-v5-irs.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=54937af6f4a0d44c2852a203d457902f3264c906
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90121 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90121
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:H/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 6.4
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: unknown
Paranoid ActionableScore: 3
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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR
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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