* [CVE-2026-98770][MODERATE 7.0] usb: gadget: midi2: Fix the jack descriptor array sizes
@ 2026-10-24 0:08 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 0:08 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98770
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: usb: gadget: midi2: Fix the jack descriptor array sizes
Commit: 8294ff75a9de23f7cc641e5e5ca31fa6ea72a574
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8294ff75a9de23f7cc641e5e5ca31fa6ea72a574
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98770
Analysis date: Fri, 23 Oct 2026 20:08:05 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
An undersized pair of MIDI2 USB gadget jack descriptor arrays allows a host administrator configuring many configfs jacks to write beyond the configuration object, creating a concrete kernel memory corruption primitive with plausible crash impact but unresolved exploitation leverage.
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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98770 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98770
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.
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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-98770 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98770 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 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:L/PR:H/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-131;CWE-119;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.7';DESCR 'The MIDI2 USB gadget configuration stores jack descriptors in fixed arrays sized for only MAX_CABLES entries, while descriptor construction can append entries for both input and output directions and require up to MAX_CABLES times 2 slots. A sufficiently large jack configuration can therefore write beyond jack_ins and jack_outs, corrupting adjacent memory and potentially crashing the kernel. For the CVSS the PR:H because reliable triggering normally requires administrative access to USB gadget configfs and control of gadget setup. The issue is locally reachable and is not triggered by network traffic or by an ordinary remote USB peer alone. Impact is at least denial of service through kernel memory corruption. In the paranoid case the OOB write may also affect confidentiality and integrity or support privilege escalation, but the available write control and exploitability require manual source level verification. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 6.7 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 LOW to MODERATE_KPANIC because the ActionableScore threshold 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 has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4. The independent weaker Aegis shadow evaluated CVSS 2.3 and ActionableScore 0 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 OOB DANGER USB SIMPLEFIX LINUS SYZBOT KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 - - checked
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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 5
* Raw paranoid score: 1
* Paranoid score: 5
* Applied conservative floor: 1 -> 5 under the controlled strong corruption manual-review floor.
* Applied paranoid floor: 1 -> 5 under the same floor. No additional speculative impact points were added.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 Strong corruption primitive. Descriptor construction can append up to twice the declared number of entries, producing an attacker-influenced out-of-bounds write past fixed arrays.
* +1 Strong DoS concern. Writing beyond the final embedded descriptor array can corrupt adjacent kernel memory and plausibly cause an Oops or kernel crash.
* -2 Proven host-admin-equivalent trigger requirement. The supplied evidence places the trigger in USB gadget configfs configuration, which normally requires effective host administrative control and gadget setup authority.
* No separate memory-layout point was awarded because it would duplicate the established OOB-write primitive.
* No confidentiality or integrity consequence point was awarded. The affected adjacent object, useful payload control, protected victim, disclosure path, and privilege-escalation chain are not established.
* No arbitrary or directed write was established. The write location follows the descriptor-array layout.
* No controlled reclaim, callback overwrite, credential modification, or LPE was demonstrated.
* No additional availability point was awarded because it would duplicate the same potential kernel crash.
* B5-R is not established. There is no retry-accumulated index, missing retry reset, or attacker-controlled retry sequence.
* V29 is not applicable. The input comes from local gadget configuration rather than descriptors supplied by a malicious physical USB peripheral.
* V33 is not established. A credible guest, namespace, or delegated-interface boundary and a specific privileged downstream consumer of corrupted adjacent state are not shown.
* B3-PENDING and B4-PENDING are not applicable. There is no shared-backing write or authorization decision bypass.
3. Reachability analysis
The actor must configure a large number of MIDI2 gadget jacks through configfs and cause descriptor construction to process both input and output entries. The supplied evidence supports a local control-plane trigger rather than network or ordinary USB-host reachability.
Effective host administrative authority over USB gadget configfs and gadget binding is required. Numeric host UID 0 is not proven to be the only possible credential, so RequiresHostUID0 remains UNKNOWN. The complete operation is not shown to work with capabilities obtained only inside an attacker-created user namespace, and control of a physical or virtual UDC generally remains host-managed. NamespaceScopedPrivilege is therefore NO for the evidenced path.
No race, retry loop, or narrow timing window is involved. Once the required administrative access and gadget environment exist, constructing the oversized jack configuration appears deterministic.
4. Primitive and severity interpretation
The exact primitive is an out-of-bounds write caused by allocating `jack_ins` and `jack_outs` for `MAX_CABLES` entries while descriptor generation can append up to `MAX_CABLES * 2` entries to each array. An overrun of `jack_ins` can overwrite the following descriptor storage, while an overrun of the final `jack_outs` array can write beyond `struct f_midi2_usb_config`.
This is not a UAF, repeated release, retry-accumulated overflow, or authorization bypass. It is CLASS_A because a concrete attacker-influenced array-size mismatch produces writes beyond the intended object bounds. The demonstrated mechanism supports kernel-memory corruption and plausible DoS. Exploitation beyond a crash remains unresolved because the allocation location, adjacent victim, descriptor-byte control, and subsequent use of corrupted neighboring state are not visible in the supplied context.
ImportantCandidate is YES because the concrete OOB-write primitive must be preserved for source-level review even though the known trigger is host-admin gated. AutoDowngradeAllowed is NO because automatically treating the issue as an ordinary configuration error would discard a real kernel-memory write primitive. This does not establish Important severity or privilege escalation by itself.
5. One-sentence report phrase
An undersized pair of MIDI2 USB gadget jack descriptor arrays allows a host administrator configuring many configfs jacks to write beyond the configuration object, creating a concrete kernel memory corruption primitive with plausible crash impact but unresolved exploitation leverage.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Review `append_config()` and its callers to determine the exact allocation class, maximum indexes, descriptor-byte control, adjacent objects, and whether corrupted state is consumed before the configuration object is discarded.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: usb: gadget: midi2: Fix the jack descriptor array sizes
Commit: 8294ff75a9de23f7cc641e5e5ca31fa6ea72a574
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8294ff75a9de23f7cc641e5e5ca31fa6ea72a574
Commit description:
The jack in/out descriptor arrays in struct f_midi2_usb_config have
the size of MAX_CABLES, which look reasonable -- but it turned out to
be incorrect. Namely, the entries for those arrays are added from
both inputs and outputs, hence for each loop cycle, it adds two, ended
up with as twice as the expected size. This inconsistency may result
in potential OOB when a large number of jacks are set up via configfs,
although the max number of cables (the loop count) is limited to
MAX_CABLES.
For addressing it, correct the jack_ins & jack_outs array sizes to
twice, MAX_CABLES * 2.
Fixes: 856fa44 ("usb: gadget: midi2: Dynamically create MIDI 1.0 altset descriptors")
Cc: stable <[email protected]>
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=c35f34092a4bc9855be6
Link: https://lore.kernel.org/[email protected]
Cc: Edward Adam Davis <[email protected]>
Signed-off-by: Takashi Iwai <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/usb/gadget/function/f_midi2.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=8294ff75a9de23f7cc641e5e5ca31fa6ea72a574
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98770 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98770
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:L/PR:H/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 6.7
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: unknown
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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