* [CVE-2026-98756][MODERATE REGULAR] usb: cdns3: Fix NULL pointer dereference in cdns3_pci_probe
@ 2026-10-24 1:27 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 1:27 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98756
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: usb: cdns3: Fix NULL pointer dereference in cdns3_pci_probe
Commit: 549c04df02f1bb5a10342f32e2c87f5d27c97279
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=549c04df02f1bb5a10342f32e2c87f5d27c97279
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98756
Analysis date: Fri, 23 Oct 2026 21:27:58 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A narrow race between enabling the first Cadence USBSS PCI function and publishing its shared driver data allows the second probe to dereference NULL and crash the kernel, with no supported remote trigger, information disclosure, privilege escalation, or reusable corruption primitive.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98756 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98756
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98756 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98756 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF V39_AEGIS_ONE_STEP_UP=LOW->MODERATE TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';CWE-362;**CWE-476;CWE-665;BEST CVSS score: '4.1';DESCR 'A race in cdns3_pci_probe can cause the second function of a Cadence USBSS PCI device to observe the first function as enabled before its shared driver data has been published. pci_get_drvdata then returns NULL and the subsequent wrapper field assignment causes a NULL pointer dereference and kernel crash. Triggering requires affected hardware and a narrow probe ordering window. Deliberate reproduction normally requires host administrative control over PCI driver binding, module loading, reprobe, or device hotplug. The issue is not network reachable and no unprivileged local interface is identified. Impact is limited to denial of service based on the available evidence. There is no supported information disclosure, privilege escalation, or reusable memory corruption primitive. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 4.1 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to MODERATE because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 4.1 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE DANGER NULLPTR USB ERRORPATH HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::
No floor or cap changes the score. The confirmed kernel crash contributes +2. The narrow one-shot probe ordering race contributes -1 because the vulnerable interleaving occurs during initialization and is not shown to be repeatedly controllable by an attacker. No additional privilege penalty is counted because it would overlap with the absence of an established nonadministrative trigger.
CVSS:3.1 conservative: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H (4.1).
CVSS:3.1 paranoid: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H (4.1).
2. Signal breakdown
* +2. A kernel crash is directly demonstrated by the call trace and NULL pointer dereference in cdns3_pci_probe.
* -1. The required state is a narrow initialization interval after the first PCI function is enabled but before pci_set_drvdata publishes the shared wrapper.
* +0. The NULL based field access does not establish an independently useful write primitive.
* +0. No UAF, OOB access, double release, stale reference, controlled reclaim, arbitrary write, information disclosure, or authorization bypass is present.
* +0. No network or ordinary unprivileged local trigger is established.
* +0. No extra availability point is awarded because it would duplicate the same kernel crash.
* +0. Confidentiality and integrity impact are not awarded merely because the NULL based assignment is technically a faulting store.
* B5-R is not applicable. There is no heap OOB write, retry-accumulated offset, or later consumption of corrupted structured state.
* B3-PENDING is not applicable. There is no shared backing or file-backed write.
* B4-PENDING is not applicable. No DENY-to-ALLOW authorization decision changes.
CWE: CWE-362, CWE-476, CWE-665.
3. Reachability analysis
The observed call path is cdns3_pci_driver_init, __pci_register_driver, driver_register, bus_add_driver, driver_attach, __driver_attach, driver_probe_device, really_probe, pci_device_probe, pci_call_probe, local_pci_probe, and cdns3_pci_probe.
The trigger requires an affected two-function Cadence USBSS PCI controller. The first function must have completed pci_enable_device or equivalent enablement while its probe has not yet published the shared wrapper with pci_set_drvdata. The second function then observes pci_is_enabled as true, receives NULL from pci_get_drvdata, and reaches the wrap devfn assignment.
No packet, USB request from an attached peripheral, syscall, ioctl, procfs entry, namespace interface, or delegated device descriptor is shown to control this ordering. Deliberate reprobe, driver binding, module loading, or PCI hotplug normally requires host-administrator-equivalent control. Therefore HostAdminRequired is YES for the supported deliberate trigger model. Numeric host UID 0 is not specifically required because capability based administration may suffice, so RequiresHostUID0 is UNKNOWN.
The complete operation is not namespace scoped. NamespaceScopedPrivilege is NO. There is no remote reachability. The race appears narrow and initialization bound. Repeated attacker-controlled attempts are not established.
4. Primitive and severity interpretation
The exact failure is a NULL based structure field assignment after pci_get_drvdata returns NULL. This is an invalid-state crash rather than an active structured-object corruption primitive. The access does not target a reclaimed object and no valid kernel object is shown to be modified.
There is no first lifetime-ending operation, surviving stale reference, or second release or refcount mutation. RealUAF is NO. The defect is neither category A fixed stale storage nor category B repeated lifetime mutation.
PrimitiveClass is CLASS_C because the demonstrated behavior is a NULL dereference and kernel DoS without reusable corruption leverage. The patch-supported consequence is a kernel crash during PCI driver probing. Privilege escalation, disclosure, arbitrary kernel modification, and controlled execution are unsupported.
ImportantCandidate is NO because no Class A or meaningful Class B primitive exists. AutoDowngradeAllowed is YES because the issue is confined to a crash-only initialization race with no unresolved security-boundary or corruption primitive. The highest defensible paranoid result remains local privileged DoS. Increasing confidentiality or integrity impact would require inventing consequences not supported by the patch or call path.
5. One-sentence report phrase
A narrow race between enabling the first Cadence USBSS PCI function and publishing its shared driver data allows the second probe to dereference NULL and crash the kernel, with no supported remote trigger, information disclosure, privilege escalation, or reusable corruption primitive.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The exact NULL dereference and crash path are established, while no UAF, OOB access, authorization bypass, cross-boundary effect, or meaningful exploitation primitive remains unresolved.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: usb: cdns3: Fix NULL pointer dereference in cdns3_pci_probe
Commit: 549c04df02f1bb5a10342f32e2c87f5d27c97279
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=549c04df02f1bb5a10342f32e2c87f5d27c97279
Commit description:
The Cadence USBSS controller is a two-function PCI device. The first
probed function allocates the driver data and stores it with
pci_set_drvdata(), while the second function reuses it via
pci_get_drvdata() when pci_is_enabled() reports that the first
function has already been probed.
When the second function is probed while the first one has been
enabled but has not yet set its driver data, pci_get_drvdata()
returns NULL, and the subsequent wrap->devfn assignment dereferences
a NULL pointer and crashes the kernel.
logs:
Call trace:
cdns3_pci_probe+0xa4/0x300
local_pci_probe+0x44/0xa8
pci_call_probe+0x54/0x158
pci_device_probe+0x84/0x100
really_probe+0x184/0x3d0
__driver_probe_device+0x80/0x178
driver_probe_device+0x44/0xe8
__driver_attach+0xec/0x1f8
bus_for_each_dev+0x7c/0xe0
driver_attach+0x28/0x38
bus_add_driver+0x110/0x238
driver_register+0x64/0x128
__pci_register_driver+0x50/0x60
cdns3_pci_driver_init+0x28/0x38
do_one_initcall+0x5c/0x280
do_initcalls+0x104/0x1d8
kernel_init_freeable+0x140/0x218
kernel_init+0x28/0x1f8
ret_from_fork+0x10/0x20
Return -EPROBE_DEFER in this case so that probing is retried after
the first function has completed its probe.
Fixes: 7733f6c ("usb: cdns3: Add Cadence USB3 DRD Driver")
Cc: stable <[email protected]>
Signed-off-by: Jie Deng <[email protected]>
Acked-by: Peter Chen <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/usb/cdns3/cdns3-pci-wrap.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=549c04df02f1bb5a10342f32e2c87f5d27c97279
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98756 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98756
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:H/PR:H/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.1
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: 1
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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