* [CVE-2026-98837][MODERATE 7.0] ALSA: caiaq: unregister the input device when probe fails
@ 2026-10-24 8:31 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 8:31 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98837
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ALSA: caiaq: unregister the input device when probe fails
Commit: 850810c12686f80cdf7530f4f21e0157d904f739
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=850810c12686f80cdf7530f4f21e0157d904f739
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98837
Analysis date: Sat, 24 Oct 2026 04:31:53 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
A failed caiaq probe can leave a registered input device whose sysfs uevent path reads name and phys strings from freed driver memory.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98837 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98837
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-2026-98837 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98837 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=3 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H';*CWE-416;*CWE-672;CWE-459;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '5.3';DESCR 'An ALSA caiaq probe failure can leave an input device registered after its backing snd_usb_caiaqdev object has been freed. The input device name and phys fields then point into freed slab memory, and reading the sysfs uevent attribute reaches input_dev_uevent and performs a confirmed use after free read. For the CVSS the PR:L value reflects that a local user can reliably read the exposed sysfs attribute, while creating the dangling state also requires a device probe failure after input registration. AC:H reflects the uncommon failure sequence and the available reproduction required a USB raw gadget plus an injected control initialization failure. The demonstrated primitive is a freed memory read that may disclose limited kernel data or cause an oops, while no write primitive or supported privilege escalation path is established. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.3 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. 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. final reconciliation stage MODERATE to MODERATE_KPANIC 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_CIANNH and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.6 and ActionableScore 3 with primitive class CLASS_B 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_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE READ USB INIT ERRORPATH UAF HARDWARE LINUS SYZBOT DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 3.
* Conservative score: 4. Real-UAF floor 4 applied: 3 -> 4.
* Raw paranoid score: 3.
* Paranoid score: 4. Same floor; no additional speculative leverage awarded.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +2 — Confirmed UAF: probe failure frees `snd_usb_caiaqdev` while a registered input device retains `name` and `phys` pointers into that freed slab object.
* +1 — Plausible limited confidentiality effect: reading the user-visible `uevent` attribute passes the stale strings through `input_dev_uevent()` and `add_uevent_var()`.
* +0 — Kernel fault is plausible, but a reliable non-KASAN host crash is not established.
* +0 — No privilege penalty: privilege for creating the dangling probe-failure state is unresolved, not proven host-admin-only.
* Floor 4 applies because the stale pointers escape probe cleanup in a still-registered device and are later consumed through sysfs, rather than being confined to an immediate destructor fault.
* Controlled reclaim, attacker-shaped replacement contents, write primitive, arbitrary read, LPE, and authorization bypass are not shown. No extra availability point is awarded.
3. Reachability analysis
A local user can plausibly read the exposed sysfs attribute after the dangling state exists. However, creating that state requires a caiaq probe failure after input registration; reproduction used a USB raw gadget and an injected `snd_usb_caiaq_control_init()` failure. The evidence does not establish who can cause the complete sequence, whether host UID 0 or administrator powers are required, or any namespace-scoped route. No timing penalty is applied merely because the setup is uncommon.
4. Primitive and severity reading
This is an active registered input object containing fixed stale pointers into freed driver state. The later operation reads those strings while formatting a uevent. It is CLASS_B lifetime corruption with a demonstrated stale read, but no stale write, repeated release, callback consumption, or controlled reuse. Limited disclosure or an Oops is plausible; stronger confidentiality, integrity, and privilege effects remain unsupported. Therefore it is not an Important candidate, and constrained Moderate downgrade remains permissible after review.
5. One-sentence report phrase
A failed caiaq probe can leave a registered input device whose sysfs uevent path reads name and phys strings from freed driver memory.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm real-world ways an attacker can induce the post-registration probe failure and whether stale slab contents are returned before faulting.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ALSA: caiaq: unregister the input device when probe fails
Commit: 850810c12686f80cdf7530f4f21e0157d904f739
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=850810c12686f80cdf7530f4f21e0157d904f739
Commit description:
setup_card() registers the input device, whose name and phys point into
struct snd_usb_caiaqdev, and then goes on to snd_card_register() and
snd_usb_caiaq_control_init(). If either fails, snd_probe() calls
snd_card_free(), which frees the device state but leaves the input
device registered: card_free() only clears the pointer, and the input
device is unregistered from snd_disconnect() alone. Reading its "uevent"
attribute afterwards dereferences freed memory:
BUG: KASAN: slab-use-after-free in string+0x4a9/0x4f0
Read of size 1 at addr ffff8880208f5043 by task caiaq/4967
add_uevent_var+0x183/0x3a0
input_dev_uevent+0x162/0x900
dev_uevent+0x2f1/0x870
uevent_show+0x1ca/0x3a0
...
Unregister the input device on the probe error path, as
snd_disconnect() does. snd_usb_caiaq_input_disconnect() is a no-op when
no input device was registered.
Reproduced with a raw-gadget Audio Kontrol 1 and a temporary hack that
makes snd_usb_caiaq_control_init() fail.
Fixes: 28abd22 ("ALSA: caiaq: Handle probe errors properly")
Cc: [email protected]
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=2a123f6269da57ffefaa
Signed-off-by: Nguyen Ngoc Thang <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Takashi Iwai <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
sound/usb/caiaq/device.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=850810c12686f80cdf7530f4f21e0157d904f739
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98837 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98837
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:U/C:L/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H
The Best / paranoid CVSS score: 5.3
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: 4
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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