[CVE-2026-68368][MODERATE 7.0] usb: gadget: f_ncm: validate datagram bounds in ncm_unwrap_ntb()

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-68368
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: usb: gadget: f_ncm: validate datagram bounds in ncm_unwrap_ntb()
Commit: e07751d0527ccc2a1c32eb0b0b7da3b4b9b5381f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e07751d0527ccc2a1c32eb0b0b7da3b4b9b5381f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68368
Analysis date: Mon, 10 Aug 2026 09:48:07 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious USB host can craft NCM NTB headers with invalid block or datagram bounds so that `ncm_unwrap_ntb()` copies adjacent kernel memory into a network skb, causing kernel memory disclosure and possible DoS on USB gadget devices exposing f_ncm.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68368 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68368

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-68368	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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:N/A:H';CWE-125;CWE-126;*CWE-200;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L';BEST CVSS score: '8.1';DESCR 'A kernel out-of-bounds read in the USB NCM gadget receive path occurs because ncm_unwrap_ntb() did not fully validate that host supplied NTB block lengths and datagram ranges stay within the available buffer. A malicious USB host can craft NTB headers with offsets or lengths beyond the declared block, or provide a secondary NTB length larger than the remaining skb data, causing skb_put_data() to copy adjacent kernel memory such as skb_shared_info into a network skb. For the CVSS the PR:N is used because the attacker does not need a local account or privileges on the victim device, only the ability to send malformed NCM traffic from the USB host side. The base vector uses AV:P because a USB host relationship normally requires physical or platform level attachment. The paranoid vector uses AV:A when the already connected USB NCM link is treated as an adjacent communication channel. Impact is primarily confidentiality loss through kernel memory disclosure, with possible denial of service if the out-of-bounds read reaches unsafe memory. Integrity impact is not assigned because the patch shows an out-of-bounds read and copy, not an overwrite primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	OOB USB SIMPLEFIX IMPROVEONLY LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	YES	NO	guess

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Network-like external data-plane trigger over USB NCM: +2
  A malicious USB host can supply crafted NTB packets to the gadget receive path. This is not Internet-remote, but it is externally supplied protocol input once the USB NCM link exists.

* Confidentiality impact plausible: +1
  The commit explicitly states that `skb_put_data()` can copy adjacent kernel memory, including data near `skb_shared_info`, into a network skb.

* Availability impact realistic: +1
  The out-of-bounds read may also lead to a crash if the invalid range crosses unsafe memory, although disclosure is the clearer primitive.

* Rare or configuration-dependent exposure: -1
  The affected path requires USB gadget mode with the NCM function enabled, which is not a default exposure on ordinary servers.

* Physical or attached-host style condition: -1
  Triggering normally requires control of the USB host side or an equivalent attached host relationship.

Paranoid adjustment:

* Treat established USB NCM as adjacent protocol reachability and avoid the full physical-only downgrade: +1 net effect
  In embedded, phone, appliance, or test-lab deployments, the USB host side can be a realistic attacker-controlled peer once connected.

Not awarded:

* No privilege escalation bonus.
  The patch shows an out-of-bounds read and kernel memory disclosure, not UAF reclaim, controlled overwrite, callback control, or type confusion.

* No integrity impact bonus.
  The described primitive copies kernel memory out. It does not write attacker-controlled data into kernel objects or shared pages.

* No strong generic memory corruption bonus.
  This is best classified as OOB read / info leak, not OOB write or heap overwrite.

## 3. Reachability analysis

The bug can be triggered by a malicious USB host sending malformed NCM NTBs to a Linux device acting as a USB gadget. No local account or Linux privileges on the victim are needed if the attacker controls the host side of the USB connection. Namespaces and containers are not the main factor here because the vulnerable input arrives through the USB gadget function rather than a local userspace API. The path is not broadly enabled on typical general-purpose servers, but it is realistic on devices that expose USB gadget networking, such as embedded systems, development boards, appliances, phones, or USB-connected test setups.

## 4. Severity interpretation

This is more than an ordinary Moderate because the patch and commit message describe a concrete kernel out-of-bounds read with possible kernel memory disclosure into a network skb. It does not currently look like an Important-class LPE because there is no write primitive, UAF reuse, object replacement, or control-flow impact shown. Realistically, the strongest demonstrated impact is confidentiality loss from kernel memory exposure, with possible DoS. The paranoid score keeps it in Actionable Moderate territory because externally supplied protocol input can trigger a real memory disclosure primitive.

## 5. One-sentence report phrase

A malicious USB host can craft NCM NTB headers with invalid block or datagram bounds so that `ncm_unwrap_ntb()` copies adjacent kernel memory into a network skb, causing kernel memory disclosure and possible DoS on USB gadget devices exposing f_ncm.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should not be auto-closed because the patch explicitly describes copying adjacent kernel memory into an skb, which is a concrete confidentiality primitive from externally supplied protocol data.

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UPSTREAM PATCH SUMMARY
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Patch: usb: gadget: f_ncm: validate datagram bounds in ncm_unwrap_ntb()
Commit: e07751d0527ccc2a1c32eb0b0b7da3b4b9b5381f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e07751d0527ccc2a1c32eb0b0b7da3b4b9b5381f

Commit description:

When unpacking host-supplied NTBs, ncm_unwrap_ntb() checks datagram length
against frame_max but does not verify that the datagram fits within the
declared block length. Additionally, when decoding multiple NTBs from a
single socket buffer, subsequent block lengths are not checked against the
actual remaining buffer data.

With these checks missing, a malicious USB host can specify datagram
offsets and lengths that point beyond the block, or supply secondary NTB
headers declaring lengths larger than the buffer. skb_put_data() then
copies adjacent kernel memory from skb_shared_info into the network skb.

Fix this by verifying that sufficient buffer space remains for the NTB
header before parsing, handling zero-length block declarations, ensuring
that block lengths never exceed the remaining buffer space, and verifying
that each datagram payload stays strictly within the block boundary.

Fixes: 427694c ("usb: gadget: ncm: Handle decoding of multiple NTB's in unwrap call")
Fixes: 2b74b0a ("USB: gadget: f_ncm: add bounds checks to ncm_unwrap_ntb()")
Cc: stable <stable@kernel.org>
Assisted-by: Jetski:Gemini-2.5-Pro
Signed-off-by: Sonali Pradhan <sonalipradhan@google.com>
Link: https://patch.msgid.link/20260703083725.1903850-1-sonalipradhan@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/gadget/function/f_ncm.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=e07751d0527ccc2a1c32eb0b0b7da3b4b9b5381f

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

The original Linux kernel CVE announcement for CVE-2026-68368 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68368

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:H/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 8.1

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: 4
  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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).