[CVE-2026-63901][MODERATE 7.0] USB: serial: digi_acceleport: fix memory corruption with small endpoints

[CVE-2026-63901][MODERATE 7.0] USB: serial: digi_acceleport: fix memory corruption with small endpoints

[AL-KERNEL]

CVE: CVE-2026-63901
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: USB: serial: digi_acceleport: fix memory corruption with small endpoints
Commit: fd34198c2e5d164b57a7dcd4692626fece319225
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fd34198c2e5d164b57a7dcd4692626fece319225
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63901
Analysis date: Sun, 19 Jul 2026 21:22:51 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious USB serial device can advertise too-small bulk-out endpoint buffers and trigger out-of-bounds access or slab corruption in the digi_acceleport driver, making this a physical-access kernel memory corruption issue with DoS impact and plausible but unproven privilege-escalation risk.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-63901 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63901

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-2026-63901	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;BEST CVSS score: '6.8';DESCR 'A malicious USB serial device can report bulk-out endpoint buffers that are smaller than the digi_acceleport driver expects. This can make the driver perform out-of-bounds memory accesses or corrupt slab memory during device startup and later port handling. For the CVSS the PR:N because the attacker does not need a user account or kernel privileges on the victim, but must be able to attach or supply a crafted USB device. The issue is physical rather than network reachable. Impact is at least denial of service through kernel memory corruption and may include confidentiality or integrity compromise because the bug class is explicit kernel memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 6)	YES	WRITE OOB USB PRINTF-TTY HARDWARE LINUS KPANIC  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

Conservative signals:

* Memory corruption, Strong corruption primitive: +2
  The commit explicitly says the missing endpoint size checks can cause out-of-bounds memory accesses or slab corruption.

* Reliable kernel crash / strong DoS: +1
  Kernel heap or slab corruption in a USB serial driver is a realistic crash path.

* Privileged kernel/device-management memory corruption path: +1
  The corruption occurs in a trusted kernel USB serial driver during device startup and port handling, based on device-reported endpoint sizes.

* Confidentiality impact plausible: +1
  Kernel slab corruption can plausibly affect adjacent kernel objects, although no concrete info leak is demonstrated.

* Integrity impact plausible: +1
  Slab corruption can plausibly corrupt kernel state, although no controlled overwrite or LPE chain is shown.

* Physical-only or rare hardware-only condition: -2
  The attacker needs to attach or supply a malicious USB device. This is not network reachable.

Conservative total: 5

Paranoid additional signal:

* Weak LPE concern: +1
  Because the patch explicitly fixes kernel slab corruption reachable from attacker-controlled USB descriptors, privilege escalation cannot be ruled out, but no reclaim, target control, callback control, or reliable overwrite primitive is demonstrated.

Paranoid total: 6

## 3. Reachability analysis

The bug is triggerable by a malicious USB serial device that reports bulk-out endpoint buffers smaller than the digi_acceleport driver expects. No local user account or kernel privilege is needed on the victim in the CVSS sense, but the attacker needs physical access or supply-chain control over a USB device. This is not remotely network reachable.

The vulnerable path is driver probe/startup for a specific USB serial driver, so exposure is narrower than core USB or generic TTY code. Auto-loading may occur if the crafted device matches the driver IDs, but practical exploitation depends on the system allowing the device to be attached and bound to the driver.

Namespaces and containers do not materially reduce the physical-access requirement. A container user generally cannot trigger this without access to USB device injection or passthrough.

Call-site confidence: high, because the changed startup path and the exact sanity checks are visible in the patch.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because the patch explicitly prevents out-of-bounds access and slab corruption in kernel space. It is not merely a validation cleanup or warning fix.

Realistically, the most likely impact is kernel crash or local system compromise risk from a malicious physical USB device. Theoretical privilege escalation is plausible due to slab corruption, but the patch does not show a reliable attacker-controlled overwrite, reclaim primitive, type confusion, or callback hijack. Therefore this is best handled as Actionable Moderate at minimum, with paranoid treatment up to the lower Important-candidate edge, but not as a clear Critical or remote Important issue.

## 5. One-sentence report phrase

A malicious USB serial device can advertise too-small bulk-out endpoint buffers and trigger out-of-bounds access or slab corruption in the digi_acceleport driver, making this a physical-access kernel memory corruption issue with DoS impact and plausible but unproven privilege-escalation risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: explicit kernel slab corruption from attacker-controlled USB device descriptors is present, and physical-only reachability lowers exposure but does not make the memory corruption safe to auto-close.

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

Patch: USB: serial: digi_acceleport: fix memory corruption with small endpoints
Commit: fd34198c2e5d164b57a7dcd4692626fece319225
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fd34198c2e5d164b57a7dcd4692626fece319225

Commit description:

Add the missing bulk-out buffer size sanity checks to avoid
out-of-bounds memory accesses or slab corruption should a malicious
device report smaller buffers 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: Sasha Levin <sashal@kernel.org>

Changed files:
  drivers/usb/serial/digi_acceleport.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=fd34198c2e5d164b57a7dcd4692626fece319225

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

The original Linux kernel CVE announcement for CVE-2026-63901 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63901

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: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).