* [CVE-2026-98265][MODERATE 7.0] ALSA: usb-audio: Clamp implicit feedback packet count to URB capacity [ Upstream
@ 2026-10-10 19:49 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-10 19:49 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98265
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ALSA: usb-audio: Clamp implicit feedback packet count to URB capacity [ Upstream
Commit: ad279ba0dc1781229f5b52f58d38d56960400e06
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ad279ba0dc1781229f5b52f58d38d56960400e06
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98265
Analysis date: Sat, 10 Oct 2026 15:49:41 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98265 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98265
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-2026-98265 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98265 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-122;CWE-129;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.8';DESCR 'A heap out of bounds write in ALSA USB audio occurs when an implicit feedback sink replaces the playback URB packet count with a larger packet count calculated from the capture endpoint. A malicious or malformed high speed UAC2 device can advertise mismatched endpoint intervals so that a playback URB allocated for one isochronous descriptor is processed as if it contained eight descriptors. The demonstrated case writes seven descriptors across 112 bytes beyond the allocated heap object and can cause slab corruption and a kernel crash. For the CVSS the PR:N value is used because a malicious USB device does not need an authenticated user account or software privileges on the target after it is attached. The base attack vector is physical for a directly connected USB device. The paranoid attack vector is adjacent because the reproducer uses USB/IP vhci and a hostile exported device may reach the host when USB/IP is configured and the device is attached. Impact is at least denial of service through kernel memory corruption. In the worst defensible case the heap write may affect adjacent kernel objects and could permit confidentiality loss integrity impact or privilege escalation. This requires manual review because exploitability beyond the demonstrated crash depends on allocator layout and control over the overwritten descriptors.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE WRITE KASAN OOB USB HARDWARE LINUS KPANIC PACKET KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 5
* Raw paranoid score: 4
* Paranoid score: 5
* Applied conservative manual-review safety floor: 4 -> 5
* Applied paranoid manual-review safety floor: 4 -> 5
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 Strong corruption primitive. A confirmed heap OOB write crosses the 208-byte URB allocation by 112 bytes. The malicious UAC2 endpoint controls the interval mismatch and therefore materially influences the number of descriptors written.
* +1 Firmware or device-mediated external influence. A malformed physical UAC2 device can supply the endpoint configuration. The USB/IP reproducer also demonstrates transport through vhci, although it does not establish unrestricted remote reachability.
* +1 Reliable kernel crash or strong DoS. KASAN directly observes multiple slab OOB writes in `prepare_playback_urb()`, and an uninstrumented kernel can suffer adjacent heap corruption or crash.
* No additional confidentiality or integrity points. No named adjacent victim, disclosure path, callback overwrite, arbitrary target, or completed privilege-escalation chain is established.
* No Strong LPE bonus. The attacker influences the overrun count, but controlled reclaim, arbitrary payload, arbitrary destination, and security-sensitive victim corruption are not demonstrated.
* No direct network-reachability bonus. USB/IP requires an exported device and host-side attachment or equivalent setup.
* No extra Availability point. It would duplicate the crash already counted.
* No hardware rarity penalty. USB audio is not rare hardware, and the supplied reproducer uses virtual USB/IP transport.
* B5-R is not established. The write results from an immediate allocation-versus-packet-count mismatch, not an index accumulated across retries. Later consumption of a specifically corrupted adjacent object is also not shown.
* B3-PENDING and B4-PENDING do not apply. There is no shared-backing write or authorization decision bypass.
3. Reachability analysis
A malicious or malformed high-speed UAC2 device can advertise capture and playback intervals that produce eight implicit-feedback packets for a playback URB allocated with one descriptor. The vulnerable write occurs after the stream starts and the first capture completion is processed.
A directly attached device provides a physical/device-mediated path. The `vhci_rx` reproducer establishes that USB/IP can transport the malicious device behavior, but it does not prove that an unauthenticated network attacker can attach a USB/IP device to the target. USB/IP attachment commonly involves separate host-side configuration, whose privilege boundary is not supplied.
The complete local privilege requirement is unresolved. ALSA PCM access may be delegated to an ordinary desktop user, but the evidence does not establish who attaches the device, who can open the affected stream, or whether one below-host-admin actor controls the complete sequence. Therefore `HostAdminRequired=UNKNOWN`. The operation is governed by USB device and ALSA device-node access rather than an attacker-created namespace capability, so `NamespaceScopedPrivilege=NO`.
No race or narrow retry window is required. Once the mismatched endpoint configuration is active, the first relevant completion can reach the overwrite.
4. Primitive and severity interpretation
The exact primitive is a heap/slab OOB write through `urb->iso_frame_desc[]`. The URB contains space for `u->packets` descriptors, but `ctx->packets` is replaced with the independently calculated implicit-feedback packet count. Playback preparation then writes descriptor fields using the larger count.
This is not a UAF, stale-storage access, repeated release, or cleanup-only fault. It is an active bounds violation against a variable-sized kernel heap object. The demonstrated writes extend into allocator-adjacent storage, but the identity and later use of the adjacent object are unknown.
The primitive is Class A because the write is concrete and the malicious device materially influences its extent. The demonstrated consequence is slab corruption and kernel DoS. Corruption of a useful neighboring object and privilege escalation are technically possible areas for review, but they are not demonstrated and receive no additional score.
`ImportantCandidate=YES` and `AutoDowngradeAllowed=NO` follow from the confirmed attacker-influenced kernel heap overwrite. Manual analysis is needed to determine attainable overwrite values, adjacent allocation types, allocator placement control, and whether USB/IP or delegated ALSA access provides a complete below-host-admin trigger.
5. One-sentence report phrase
A malicious UAC2 implicit-feedback configuration can make ALSA write multiple isochronous descriptors beyond a playback URB allocation, causing concrete kernel heap corruption and a crash while leaving adjacent-object exploitation unresolved.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The patch establishes a real attacker-influenced heap OOB write, while overwrite-value control, adjacent victims, complete attacker privilege, and exploitation beyond DoS remain unresolved.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ALSA: usb-audio: Clamp implicit feedback packet count to URB capacity [ Upstream
Commit: ad279ba0dc1781229f5b52f58d38d56960400e06
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ad279ba0dc1781229f5b52f58d38d56960400e06
Changed files:
sound/usb/pcm.c
sound/usb/endpoint.c
drivers/usb/core/hcd.c
drivers/usb/usbip/vhci_rx.c
kernel/kthread.c
sound/usb/card.h
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=ad279ba0dc1781229f5b52f58d38d56960400e06
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98265 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98265
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:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 8.8
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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