[CVE-2026-64335][LOW] USB: serial: digi_acceleport: fix broken rx after throttle

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

CVE: CVE-2026-64335
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: USB: serial: digi_acceleport: fix broken rx after throttle
Commit: 4f3f6f44db71e469933a7c36c5d57d937ba0a21b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4f3f6f44db71e469933a7c36c5d57d937ba0a21b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64335
Analysis date: Sat, 25 Jul 2026 07:07:28 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A local user with access to a Digi AccelePort USB serial tty can leave RX disabled after closing the port while throttled, causing device-level denial of service until reconnect or driver rebind.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-64335 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64335

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: LOW
Manual review required: NO

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-2026-64335	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-664;CWE-404;CWE-703;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'The Digi AccelePort USB serial driver can lose receive functionality when a port is closed while it is throttled because the read URB is not submitted again on the next open. A local user or process with access to the tty device can trigger the condition by using the port in a way that leaves the throttle restart state set before close. For the CVSS the PR:L is used because reliable triggering requires local access to the serial device node but not full administrator privileges. The issue is not network reachable and does not indicate memory corruption or privilege escalation. Impact is denial of service for the affected serial receive path until device reconnect or driver rebind.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	LOCK USB PRINTF-TTY SIMPLEFIX ERRORPATH HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

* Local unprivileged trigger: +1. A local user or process with access to the affected tty device may open, throttle, close, and reopen the port.
* Availability impact realistic: +1 in the paranoid interpretation. RX remains broken until device reconnect or driver rebind, but the impact is limited to the affected USB serial port.
* Rare AND difficult-to-reach subsystem/configuration: -1 for conservative scoring. This requires Digi AccelePort USB serial hardware and access to that device node.
* No memory corruption signal. The patch only clears throttle state and resubmits a read URB.
* No privilege escalation signal. There is no UAF, OOB write, stale callback, type confusion, refcount misuse, or attacker-controlled overwrite.
* No network reachability. The affected path is local tty open/close handling.

## 3. Reachability analysis

The bug is triggerable only by a local actor that can access the Digi AccelePort USB serial tty device. Namespaces or containers matter only if the device node is delegated into the container. The path is not broadly default-exposed because it depends on specific USB serial hardware and driver use. Realistic exploitation is a per-device availability failure, not a host-wide compromise.

## 4. Severity interpretation

This behaves like a Low or ordinary Moderate availability bug. The theoretical impact is persistent loss of receive functionality for the affected serial port, but there is no evidence of kernel memory corruption, privilege escalation, information disclosure, or system-wide crash. The paranoid score keeps the persistent device-level DoS in mind, but it still does not reach Actionable Moderate.

## 5. One-sentence report phrase

A local user with access to a Digi AccelePort USB serial tty can leave RX disabled after closing the port while throttled, causing device-level denial of service until reconnect or driver rebind.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch fixes a localized state-management bug in a rare USB serial driver, with no memory corruption or security-boundary bypass evidence.

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

Patch: USB: serial: digi_acceleport: fix broken rx after throttle
Commit: 4f3f6f44db71e469933a7c36c5d57d937ba0a21b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4f3f6f44db71e469933a7c36c5d57d937ba0a21b

Commit description:

If the port is closed while throttled, the read urb is never resubmitted
and the port will not receive any further data until the device is
reconnected (or the driver is rebound).

Clear the throttle flags and submit the urb if needed when opening the
port.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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=4f3f6f44db71e469933a7c36c5d57d937ba0a21b

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

The original Linux kernel CVE announcement for CVE-2026-64335 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64335

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:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 1
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).