* [CVE-2026-98836][IMPORTANT] ALSA: line6: reject oversized playback packets
@ 2026-10-24 1:16 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-24 1:16 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98836
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: ALSA: line6: reject oversized playback packets
Commit: a84371be89c39ccc46c7af8b9eb15c448df9265f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a84371be89c39ccc46c7af8b9eb15c448df9265f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98836
Analysis date: Fri, 23 Oct 2026 21:16:48 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A malicious Line6 compatible USB device can advertise asymmetric endpoint packet sizes that cause an attacker influenced heap out of bounds write during playback URB preparation, requiring mandatory manual review despite the physical attack prerequisite and constrained payload.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98836 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98836
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: IMPORTANT
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-2026-98836 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-98836 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=3 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;*CWE-20;CWE-131;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.8';DESCR 'An out of bounds heap write occurs in the ALSA Line6 playback path because submit_audio_out_urb() derives fsize from the USB IN endpoint or the sample rate but writes into a slice allocated according to the smaller OUT endpoint packet size. A malicious or malformed USB device can advertise a large IN wMaxPacketSize and a small OUT wMaxPacketSize, causing memcpy() or memset() to write beyond the playback slice and potentially beyond the allocated kmalloc object. USB core validation does not prevent the corruption because it occurs after the write and high speed isochronous validation may accept a transfer length scaled by the endpoint multiplier. For the CVSS the PR:N value is used because an attacker controlling the USB device does not require an account or software privileges on the target system. Physical access or equivalent control of an attached USB device is normally required, so the issue is not network reachable. Impact is at least denial of service through a kernel crash. The confirmed heap out of bounds write may also corrupt adjacent kernel objects and could potentially affect confidentiality and integrity, although reliable privilege escalation is not demonstrated and the written data may be limited to playback data or zeros. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 6.8 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 MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to IMPORTANT because a specific evidence based protection or manual review veto was applied. final reconciliation stage IMPORTANT to IMPORTANT because KP specialist did not establish a qualifying panic. 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 produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and V42_LEGACY_CLASSA_FD_VETO and MANUAL_REVIEW_REQUIRED and TEMP_KPANIC_MERGE_IMPORTANT_WINS and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 4.3 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 IMPORTANT.';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 ERRORPATH HARDWARE LINUS PACKET INCREASED_TO_HIGH_BASED_ON_GUESSCVSS V42_LEGACY_CLASSA_FD_VETO MANUAL_REVIEW_REQUIRED TEMP_KPANIC_MERGE_IMPORTANT_WINS KPANIC_UNSUPPORTED_REMOVED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 0
* Conservative score: 5
* Raw paranoid score: 0
* Paranoid score: 5
* Applied V29 physical-device-descriptor heap-overwrite preservation calibration: 0 -> 5.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
The conservative and paranoid scores are identical because the confirmed primitive is already preserved, while no stronger controlled target, payload, reclaim, disclosure, or privilege-escalation mechanism is established.
2. Signal breakdown
Positive signals:
* +2 Strong corruption primitive. A confirmed heap/slab out-of-bounds write occurs before `usb_submit_urb()`, and the KASAN trace shows a 1024-byte write beyond a 256-byte `kmalloc` object.
* +1 Reliable kernel crash or strong DoS concern. Corruption occurs in a kernel workqueue and can damage adjacent slab storage. KASAN already detects the invalid write.
* V29 applies. Peripheral-controlled endpoint descriptors determine incompatible IN and OUT packet sizes, while the resulting `memcpy()` or `memset()` exceeds the allocation derived from the OUT endpoint. Descriptor influence over write size is sufficient for CLASS_A preservation under V29.
Negative signals:
* -2 Physical or specialized hardware prerequisite. Triggering requires a malicious or malformed Line6-compatible USB device, modified device firmware, or equivalent control over the attached peripheral and its endpoint descriptors.
* -1 No attacker-selected destination or general payload. The destination is the playback buffer and the overflow data consists of playback bytes or zeros. No arbitrary address selection is established.
Non-awarded signals:
* Controlled reclaim or replacement is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated.
* A named adjacent victim object is not identified.
* Confidentiality impact, credential corruption, callback control, and LPE are not demonstrated.
* No additional Availability point is awarded for the same possible kernel crash.
* NEW52 B5-R does not apply. The overflow is not shown to accumulate through retries or a missing retry-state reset.
* V33 does not independently apply. Corruption of a specific active structured object, its privileged consumer, and a concrete trust boundary are not identified.
* B3-PENDING and B4-PENDING do not apply. There is no shared-backing write or authorization decision bypass.
3. Reachability analysis
The evaluated attacker controls a physical USB peripheral or its firmware. A device can advertise a large IN `wMaxPacketSize` and a smaller OUT `wMaxPacketSize`, causing `prev_fsize` or the synthesized startup size to exceed the playback slice.
No host account, UID 0, capability, namespace privilege, or host-administrator power is required by that peripheral attacker. Therefore `HostAdminRequired=NO` and `RequiresHostUID0=NO`. Namespace privileges are not part of this path, so `NamespaceScopedPrivilege=NO`.
The supplied call trace reaches the write through `line6_startup_work`, indicating that driver startup can exercise the vulnerable path. Direct network reachability and ordinary local-userspace triggerability are not established. The issue requires Line6 driver support and a physically attached or equivalently controlled USB device. No race or retry timing is required.
4. Primitive and severity interpretation
The exact primitive is an attacker-influenced heap out-of-bounds write caused by an allocation and packet-size mismatch. The driver allocates each playback slice according to `max_packet_size_out`, but derives `fsize` from the IN endpoint packet length or sample rate and performs the write without checking that it fits.
This is not a UAF, stale-storage access, repeated refcount mutation, or authorization bypass. It is a direct overwrite of heap storage adjacent to a fixed playback allocation.
The demonstrated consequence is corruption beyond the allocated `kmalloc` object, with kernel crash or DoS as the most defensible operational impact. The speculative consequence is corruption of a security-relevant adjacent slab object, but the patch does not establish target selection, useful payload control, information disclosure, callback influence, or privilege escalation.
`PrimitiveClass=CLASS_A` follows the V29 profile because a malicious peripheral can influence descriptor values that determine the confirmed overwrite size. `ImportantCandidate=YES` and `AutoDowngradeAllowed=NO` preserve this concrete kernel heap-write primitive for human analysis. Physical access limits exposure but does not turn the write into a crash-only invalid read.
5. One-sentence report phrase
A malicious Line6 compatible USB device can advertise asymmetric endpoint packet sizes that cause an attacker influenced heap out of bounds write during playback URB preparation, requiring mandatory manual review despite the physical attack prerequisite and constrained payload.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The patch establishes a real heap overwrite beyond a `kmalloc` object. Manual review should determine possible adjacent slab objects and whether playback data or zero-filled writes can corrupt security-relevant active state.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ALSA: line6: reject oversized playback packets
Commit: a84371be89c39ccc46c7af8b9eb15c448df9265f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a84371be89c39ccc46c7af8b9eb15c448df9265f
Commit description:
Each playback URB is handed a slice of out.buffer that is exactly
LINE6_ISO_PACKETS * max_packet_size_out bytes, sized from the OUT
endpoint, but the number of bytes written into that slice is never
compared against it.
submit_audio_out_urb() takes the frame count from prev_fsize, which
audio_in_callback() derived from the *IN* endpoint's received packet
length, and rescales it with the playback frame size; when prev_fsize is
still zero it synthesizes a length from the sample rate instead. On a
device declaring a large IN wMaxPacketSize and a small OUT
wMaxPacketSize, the resulting memcpy(), or the memset() when the
playback stream is idle, runs past its slice and, as the reproducer
below shows, beyond the allocation.
usb_submit_urb() is not a backstop. max_packet_size_out comes from
usb_maxpacket(), which returns only the low 11 bits of wMaxPacketSize,
while USB core validates a high-speed isochronous length against that
base scaled by usb_endpoint_maxp_mult(). A length of up to three times
the allocated slice is therefore accepted, and even a rejected URB is
only rejected after the write.
Reject a packet that does not fit the slice the driver allocated for it.
Clamping it instead would silently shorten the capture-derived rate
feedback and desynchronize the two streams.
BUG: KASAN: slab-out-of-bounds in submit_audio_out_urb (sound/usb/line6/playback.c:229)
Write of size 1024 at addr ffff888100bbd400 by task kworker/1:2/5002
Workqueue: events line6_startup_work
Call Trace:
__asan_memcpy (mm/kasan/shadow.c:106)
submit_audio_out_urb (sound/usb/line6/playback.c:229)
line6_submit_audio_out_all_urbs (sound/usb/line6/playback.c:291)
line6_stream_start (sound/usb/line6/pcm.c:194)
line6_pcm_acquire (sound/usb/line6/pcm.c:337)
line6_startup_work (sound/usb/line6/driver.c:728)
process_one_work (kernel/workqueue.c:3396)
worker_thread (kernel/workqueue.c:3479 kernel/workqueue.c:3560)
kthread (kernel/kthread.c:436)
ret_from_fork (arch/x86/kernel/process.c:158)
ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
The buggy address belongs to the object at ffff888100bbd400
which belongs to the cache kmalloc-256 of size 256
The buggy address is located 0 bytes inside of
allocated 256-byte region [ffff888100bbd400, ffff888100bbd500)
Cc: [email protected]
Fixes: 7a0f55a ("ALSA: line6: Support assymetrical in/out configurations")
Reported-by: <[email protected]>
Assisted-by: LLM
Signed-off-by: Xiang Mei <[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/line6/playback.c
mm/kasan/shadow.c
sound/usb/line6/pcm.c
sound/usb/line6/driver.c
kernel/workqueue.c
kernel/kthread.c
arch/x86/kernel/process.c
arch/x86/entry/entry_64.S
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=a84371be89c39ccc46c7af8b9eb15c448df9265f
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98836 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98836
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:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 6.8
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: IMPORTANT
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): IMPORTANT
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).
^ permalink raw reply [relevance 21%]
Results 1-1 of 1 | reverse | sort options + mbox downloads above
-- links below jump to the message on this page --
2026-10-24 1:16 21% [CVE-2026-98836][IMPORTANT] ALSA: line6: reject oversized playback packets AL-KERNEL
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox