[CVE-2026-98312][MODERATE REGULAR] ALSA: 6fire: fix OOB write from device-reported iso length [ Upstream

[CVE-2026-98312][MODERATE REGULAR] ALSA: 6fire: fix OOB write from device-reported iso length [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98312
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ALSA: 6fire: fix OOB write from device-reported iso length [ Upstream
Commit: 61e665fb48e9eee44ec6d610514af383b1802cc1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=61e665fb48e9eee44ec6d610514af383b1802cc1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98312
Analysis date: Fri, 09 Oct 2026 12:51:15 -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-2026-98312 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98312

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-2026-98312	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98312 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=3 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H';*CWE-787;CWE-191;CWE-131;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.1';DESCR 'A heap out of bounds write occurs in usb6fire_pcm_in_urb_handler because the driver derives outgoing packet lengths from the device reported actual_length without first guarding the unsigned subtraction or limiting the result to the OUT endpoint packet size. A packet with actual_length below 4 causes an integer underflow and produces a very large length that reaches memset. A full valid input packet can also exceed the 4832 byte output buffer after 4 input channels are scaled to 6 output channels at 88.2 or 96 kHz. The write occurs before usb_submit_urb can reject the oversized descriptor and can cause a kernel panic. For the CVSS the PR:N value is used because a malicious USB device or USB/IP endpoint does not need an authenticated account or privileges on the target after it has been attached. The direct attack vector is physical USB access. A network adjacent USB/IP scenario is also plausible when a user attaches an attacker controlled exported device. Impact is at least denial of service and the confirmed heap out of bounds write may corrupt adjacent kernel objects. In the worst defensible case this could affect confidentiality and integrity or support privilege escalation, but reliable exploitation would require control of heap layout and written data.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	WRITE KASAN OOB USB INIT LOG HARDWARE LINUS PACKET  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=3
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
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

* +1 Constrained kernel buffer overwrite. Device-reported `actual_length` causes a confirmed heap OOB write through `memset()` and potentially through the PCM copy, but the destination begins in a fixed URB buffer and useful target selection is not established.
* +1 Reliable kernel crash. KASAN confirms the OOB write and the supplied trace ends in a fatal exception and kernel panic.
* +1 Firmware or device-mediated external influence. A USB device or attached USB/IP endpoint controls the isochronous completion length used in the vulnerable calculation.
* No remote-reachability bonus. USB/IP appears in the reproducer, but an attacker cannot be assumed to attach a remote USB endpoint without a separate local setup step.
* No local-unprivileged bonus. Access to the complete PCM, USB device, and USB/IP attachment sequence is not established for an ordinary user.
* No strong-corruption bonus. The payload is primarily zero-filled or derived from PCM data, the initial target is a fixed IO buffer, and no adjacent victim, directed destination, callback, or arbitrary-write primitive is shown.
* No C or I bonus. Adjacent kernel-object corruption is possible, but no protected object, disclosure, controlled state modification, or privilege-escalation chain is established.
* No extra Availability point. The panic is already counted as the reliable-crash signal.
* No hardware or niche penalty. The device is specialized, but the `vhci_rx` trace demonstrates a virtual USB/IP path, so physical-only or rare-hardware-only reachability is not established.

B5-R evaluation:

* Gate 1 is satisfied. A heap OOB write is confirmed.
* Gate 2 is not satisfied. `total_length` accumulates across the fixed packet descriptors of one URB, not across retries or re-entry because of a missing retry reset.
* Gate 3 is unresolved. Device input controls `actual_length`, but below-host-admin control of the complete USB/IP attachment and PCM activation sequence is not established.
* Gate 4 is not satisfied. The oversized descriptor is later rejected by `usb_submit_urb`, but the evidence does not show that an object corrupted by the OOB write is subsequently consumed as valid structured state.
* Gate 5 alone cannot establish the profile.
* Therefore, the B5-R Important-preservation rule does not apply.

3. Reachability analysis

The direct trigger is a malformed or unusual isochronous completion from a TerraTec 6Fire-compatible USB device. A zero-length packet can trigger the unsigned underflow, while ordinary maximum-sized packets at 88.2 or 96 kHz can produce a smaller cumulative overflow.

The supplied trace proves that a virtual USB/IP device can reach the handler. It does not establish that a network attacker can independently attach that endpoint to the victim. USB/IP attachment commonly involves a local control-plane operation, but the exact privilege requirement is not supplied. Consequently, host-admin privilege and namespace-scoped privilege remain unknown.

No race is involved. Once the device reports the relevant lengths while the PCM path is active, the vulnerable arithmetic and writes occur deterministically.

4. Primitive and severity interpretation

The exact primitive is a heap OOB write caused by unsigned subtraction underflow or by cumulative packet lengths exceeding the 4832-byte output buffer. This is not a UAF, retry-accumulated corruption, or repeated lifetime operation.

The affected storage is a fixed URB output buffer. The attacker-influenced input controls write length, but the demonstrated write is predominantly a zeroing operation, and neither an arbitrary destination nor a security-sensitive adjacent object is identified. The later PCM copy may place user PCM data according to the invalid lengths, but the evidence does not establish one below-host-admin principal controlling the complete device-length and PCM-data sequence for exploitation.

This is CLASS_B because real kernel memory corruption is confirmed, but its exploitation leverage is constrained. The demonstrated consequence is host kernel panic. Adjacent-object corruption and privilege escalation remain speculative.

ImportantCandidate is NO because the B5-R chain is incomplete and there is no controlled target, useful corrupted-state consumption, arbitrary write, disclosure, or demonstrated LPE. AutoDowngradeAllowed is YES because the established primitive is a constrained fixed-buffer overwrite with crash as the only demonstrated security consequence. Manual review remains recommended due to the confirmed heap write and uncertain USB/IP reachability.

5. One-sentence report phrase

A device-controlled isochronous packet length can underflow or exceed the ALSA 6fire output buffer calculation, causing a constrained heap out-of-bounds write and kernel panic, while useful adjacent-object corruption and below-host-admin USB/IP reachability remain unproven.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The heap OOB write is concrete, but the B5-R retry and corrupted-state-consumption gates are not established, and the complete attacker privilege boundary for USB/IP is unresolved.

7. Call-site confidence

Call-site confidence: high

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: ALSA: 6fire: fix OOB write from device-reported iso length [ Upstream
Commit: 61e665fb48e9eee44ec6d610514af383b1802cc1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=61e665fb48e9eee44ec6d610514af383b1802cc1

Changed files:
  sound/usb/6fire/pcm.c
  lib/dump_stack.c
  mm/kasan/report.c
  mm/kasan/generic.c
  mm/kasan/shadow.c
  drivers/usb/core/hcd.c
  drivers/usb/usbip/vhci_rx.c
  kernel/kthread.c
  arch/x86/kernel/process.c
  arch/x86/entry/entry_64.S
  mm/slub.c
  sound/usb/6fire/chip.c
  drivers/usb/core/driver.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=61e665fb48e9eee44ec6d610514af383b1802cc1

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98312 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98312

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:H/PR:N/UI:R/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.1

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: 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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).