[CVE-2026-63928][MODERATE 7.0] USB: serial: omninet: fix memory corruption with small endpoint

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

CVE: CVE-2026-63928
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: USB: serial: omninet: fix memory corruption with small endpoint
Commit: 180996f0ca774001944e4afa452d569ba2f6455c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=180996f0ca774001944e4afa452d569ba2f6455c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63928
Analysis date: Sun, 19 Jul 2026 16:41:46 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious USB serial device can report a too-small bulk-out endpoint size, causing the omninet driver to use a hardcoded larger transfer size and potentially trigger user-controlled kernel slab corruption with DoS and possible privilege escalation impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-63928 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63928

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-2026-63928	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-122;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H';BEST CVSS score: '6.8';DESCR 'A malicious USB serial device can report a bulk out endpoint max packet size smaller than the hardcoded omninet transfer size. When the driver later prepares a write buffer, the transfer can exceed the allocated bulk out buffer and cause user controlled slab corruption in kernel memory. For the CVSS the PR:N is used in the paranoid score because the malicious device can provide crafted USB descriptors without privileges on the target host. The issue is not network reachable and requires a physical or peripheral attack path. Impact is at least denial of service via kernel memory corruption and in the worst case may allow confidentiality or integrity impact including privilege escalation, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 6)	YES	WRITE OOB USB PRINTF-TTY SIMPLEFIX HARDWARE LINUS KPANIC PACKET  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Memory corruption, strong corruption primitive: +2
  The commit explicitly states user-controlled slab corruption due to a malicious USB device reporting a bulk-out endpoint smaller than the hardcoded transfer size.

* Privilege escalation plausible: +2 paranoid, +1 conservative
  Kernel slab corruption can plausibly be exploitable beyond DoS, but the primitive is peripheral-triggered and not enough is shown to claim a strong reliable LPE path.

* Firmware-mediated or external device influence: +1
  The attacker-controlled input comes from a malicious USB device descriptor or endpoint configuration.

* Reliable kernel crash / strong DoS: +1
  A too-small bulk-out buffer combined with a larger hardcoded transfer can corrupt slab memory and plausibly crash the kernel.

* Privileged kernel/device-management memory corruption path: +1
  The corruption occurs inside a USB serial kernel driver during device handling and buffer setup.

* Physical-only or rare hardware-only condition: -2
  The issue requires a malicious or compromised USB peripheral, so it is not network reachable and not a normal local syscall-only attack.

## 3. Reachability analysis

A malicious USB serial device can trigger the vulnerable condition by advertising a smaller bulk-out endpoint max packet size than the driver expects. No target-host privileges are needed for the device to present crafted USB descriptors, but practical triggering requires physical access, malicious peripheral insertion, or an equivalent USB redirection scenario.

Namespaces and containers do not materially help ordinary unprivileged users unless they can influence USB device attachment or access the resulting serial device path. The affected driver is not a core default network path, but USB serial drivers are commonly available on general-purpose Linux systems. Call-site confidence: medium, because the patch shows the driver configuration fix and the commit describes the corruption, but not the full write-buffer call path.

## 4. Severity interpretation

This is more than an ordinary Moderate correctness issue because the commit explicitly identifies user-controlled slab corruption. It is not a network bug and is constrained by physical/peripheral reachability, which prevents it from being a high-end Important candidate by default.

Realistic impact is likely kernel crash or host compromise risk from a malicious USB device. Theoretical impact includes privilege escalation due to kernel heap corruption, but the patch does not demonstrate a reliable reclaim, target selection, or full exploit primitive. Therefore this should be treated as Actionable Moderate at minimum, with manual review required.

## 5. One-sentence report phrase

A malicious USB serial device can report a too-small bulk-out endpoint size, causing the omninet driver to use a hardcoded larger transfer size and potentially trigger user-controlled kernel slab corruption with DoS and possible privilege escalation impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

The issue involves explicit user-controlled kernel slab corruption in a USB driver. Even though the attack path is physical/peripheral rather than network reachable, memory corruption with possible privilege escalation should not be auto-closed.

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UPSTREAM PATCH SUMMARY
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Patch: USB: serial: omninet: fix memory corruption with small endpoint
Commit: 180996f0ca774001944e4afa452d569ba2f6455c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=180996f0ca774001944e4afa452d569ba2f6455c

Commit description:

Make sure that the bulk-out buffers are at least as large as the
hardcoded transfer size to avoid user-controlled slab corruption should
a malicious device report a smaller endpoint max packet size than
expected.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/serial/omninet.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=180996f0ca774001944e4afa452d569ba2f6455c

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

The original Linux kernel CVE announcement for CVE-2026-63928 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63928

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:R/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: 5
  Paranoid ActionableScore: 6

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).