[CVE-2026-74641][IMPORTANT] ALSA: usx2y: bound the hwdep mmap fault offset

[CVE-2026-74641][IMPORTANT] ALSA: usx2y: bound the hwdep mmap fault offset

[AL-KERNEL]

CVE: CVE-2026-74641
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: ALSA: usx2y: bound the hwdep mmap fault offset
Commit: 10a87401fb3148c388e55df0148295b3b137da07
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=10a87401fb3148c388e55df0148295b3b137da07
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74641
Analysis date: Sat, 22 Aug 2026 16:16:31 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
ALSA usx2y hwdep mmap fault handling lacks an offset bound check, allowing a local process with access to the device node to map unintended kernel pages read-write, which can cause a kernel crash and plausibly enable kernel memory disclosure or local privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74641 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74641

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-74641	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-823;*CWE-787;CWE-125;CWE-668;BEST CVSS score: '7.8';DESCR 'ALSA usx2y hwdep mmap fault handling can use an attacker controlled page offset without a bounds check and convert an address outside the shared buffer into a mapped struct page. A local process that can open the hwdep node for an attached US-X2Y device can choose the mmap offset and may obtain read-write access to kernel memory outside the intended object. For the CVSS the PR:L is used because triggering requires local code execution and access to the device node, but no special capability check is described. The issue is not network reachable. Impact can include local denial of service, kernel memory disclosure, kernel memory modification, and plausible privilege escalation because the primitive maps unintended kernel pages into user space read-write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-74641 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	READ OOB USB HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local process can reach the path by opening the ALSA hwdep node for an attached US-X2Y device. The commit states that no capability check is involved.

* Strong LPE plausibility: +2
  The bug can map a kernel page outside the intended shared-memory object into user space with read-write permissions. This is a plausible local privilege escalation primitive, not just a crash.

* Memory corruption, strong corruption primitive: +2
  The attacker controls the mmap page offset and can cause `virt_to_page()` to resolve a page outside the allocated object, then install it into the caller VMA read-write.

* Reliable kernel crash / strong DoS: +1
  The commit includes an observed kernel Oops when the chosen offset lands in an unpopulated vmemmap region.

* Confidentiality impact plausible: +1
  Mapping unintended kernel memory into user space can expose kernel data.

* Integrity impact plausible: +1
  The mapped page is read-write, so unintended kernel memory can potentially be modified.

* Availability impact realistic: +1 in paranoid score only
  A bad offset can produce an Oops, and successful writable mappings can also destabilize the kernel. This is counted only in the paranoid score to avoid double-counting the corruption primitive.

* Physical-only or rare hardware-only condition: -2
  Exploitation requires an attached US-X2Y device and access to its hwdep node, which limits broad exposure.

Call-site confidence: high. The vulnerable fault handlers and their direct behavior are present in the supplied patch context.

## 3. Reachability analysis

The trigger is local. A process needs access to the ALSA hwdep character device for an attached US-X2Y device and must reach the state after FPGA image loading through the same node. No capability check is described, so this is not treated as PR:H. Device-node permissions may restrict access in practice, for example to root or an audio-related group, but the kernel path itself is not capability-gated.

The issue is not network reachable. Containers and namespaces generally do not help unless the device node is passed into the container. The affected driver is not a broad default attack surface because it depends on uncommon USB audio hardware, but when the device node is accessible the primitive is strong.

## 4. Severity interpretation

This behaves more like an Important-class local kernel vulnerability than an ordinary Moderate issue. The realistic exploitation evidence includes both a demonstrated crash path and a stronger primitive where a user-selected mmap offset can expose an unintended kernel page read-write. The main limiting factor is hardware and device-node availability, not weakness of the bug class.

Theoretical impact includes local privilege escalation through writable kernel memory exposure. Realistic exploitation still requires careful target-page selection and a reachable device node, so the conservative score remains below Critical-like handling.

## 5. One-sentence report phrase

ALSA usx2y hwdep mmap fault handling lacks an offset bound check, allowing a local process with access to the device node to map unintended kernel pages read-write, which can cause a kernel crash and plausibly enable kernel memory disclosure or local privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should be manually reviewed because the patch fixes a direct read-write kernel page exposure primitive from a local mmap interface, with plausible confidentiality, integrity, and privilege-escalation impact despite the rare-hardware requirement.

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

Patch: ALSA: usx2y: bound the hwdep mmap fault offset
Commit: 10a87401fb3148c388e55df0148295b3b137da07
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=10a87401fb3148c388e55df0148295b3b137da07

Commit description:

snd_us428ctls_vm_fault() turns the faulting page offset into a kernel
address with no bound of any kind:

	offset = vmf->pgoff << PAGE_SHIFT;
	vaddr = (char *)(...)->us428ctls_sharedmem + offset;
	page = virt_to_page(vaddr);
	get_page(page);
	vmf->page = page;

	return 0;

snd_us428ctls_mmap() checks only the length of the mapping, never the
offset, and us428ctls_sharedmem is a single page from
alloc_pages_exact().  For a character device file_mmap_size_max()
returns ULONG_MAX, so the mm layer imposes no ceiling either.  Every page
offset above zero resolves to a struct page outside the object, and the
handler installs it into the caller's address space read-write; the vma
is not marked read-only.

The caller picks the page frame with a single mmap() argument and gets
read-write access to a page of kernel memory it does not own; an offset
that lands in an unpopulated vmemmap region oopses instead.

A process that can open the hwdep node of an attached US-X2Y reaches
this after loading the FPGA image through the same node; no capability
check is involved.

On 7.2.0-rc5 (arm64), mmap() with a large offset:

  Unable to handle kernel paging request at virtual address fffffdffc45d5ac8
  pc : snd_us428ctls_vm_fault+0x68/0x140 [snd_usb_usx2y]
  Call trace:
   snd_us428ctls_vm_fault+0x68/0x140 [snd_usb_usx2y]
   __do_fault
   __handle_mm_fault
   handle_mm_fault
   el0_da

Reject any offset outside the shared region.  The pcm hwdep handler in
usx2yhwdeppcm.c computes its address the same way and needs the same
bound.

Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>

Fixes: 1da177e ("Linux-2.6.12-rc2")
Reported-by: Federico Kirschbaum <federico.kirschbaum@xbow.com>
Reported-by: Baul Lee <baul.lee@xbow.com>
Cc: stable@vger.kernel.org
Signed-off-by: Baul Lee <baul.lee@xbow.com>
Link: https://patch.msgid.link/20260805013445.38283-1-baul.lee@xbow.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/usb/usx2y/usX2Yhwdep.c
  sound/usb/usx2y/usx2yhwdeppcm.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=10a87401fb3148c388e55df0148295b3b137da07

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

The original Linux kernel CVE announcement for CVE-2026-74641 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74641

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 6
  Paranoid ActionableScore: 7

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