[CVE-2026-72403][LOW] ALSA: FCP: Fix NULL pointer dereference in interface lookup [ Upstream

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

CVE: CVE-2026-72403
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ALSA: FCP: Fix NULL pointer dereference in interface lookup [ Upstream
Commit: f28d7b5f1578a7501ab17b10643ed1e4f729187e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f28d7b5f1578a7501ab17b10643ed1e4f729187e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72403
Analysis date: Sat, 15 Aug 2026 21:28:41 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-72403 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72403

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-72403	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;CWE-754;BEST CVSS score: '4.6';DESCR 'A NULL pointer dereference in the ALSA/FCP USB driver occurs because fcp_find_fc_interface() can select a vendor specific interface and then read endpoint 0 without checking that any endpoint descriptors exist. A malformed physical USB device can expose bNumEndpoints as 0, causing get_endpoint(..., 0) to produce an invalid endpoint descriptor pointer and usb_endpoint_num() to dereference it. For the CVSS the PR:N is used because the attacker does not need an authenticated local account on the target system, only the ability to present a crafted USB device. The attack vector is physical rather than network reachable. Impact is denial of service via kernel crash or oops, with no supported confidentiality or integrity impact from the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	NULLPTR USB SIMPLEFIX HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=1
ActionableScoreLower=0

1. **ActionableScore**

* Conservative score: **0**
* Paranoid score: **1**
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. **Signal breakdown**

Triggered signals:

* Reliable kernel crash / strong DoS: **+1**
  The malformed USB device can cause a NULL pointer dereference in `usb_endpoint_num()` after `get_endpoint(..., 0)` is used on an interface with `bNumEndpoints == 0`.

* Physical-only or rare hardware-only condition: **-2**
  The attacker must present a crafted physical USB device or equivalent USB emulation to the target. This is not remotely network reachable.

Paranoid-only interpretation:

* Firmware-mediated external influence: **+1**
  A malicious USB device controls descriptors consumed by the kernel driver. This is still physical/device-mediated, not network reachable.

Not awarded:

* Generic memory corruption: **+0**
  This is a NULL pointer dereference, not UAF, OOB write, double free, type confusion, or arbitrary write.

* Privilege escalation plausible: **+0**
  No reclaim primitive, writable corruption sink, callback control, refcount abuse, or attacker-controlled object replacement is shown.

* Confidentiality / Integrity impact: **+0**
  The patch supports DoS only.

* Availability impact realistic: **+0 additional**
  Availability is already counted through the reliable crash signal. No persistent filesystem, storage, or cross-workload impact is indicated.

Call-site confidence: **high**. The changed check is directly adjacent to the unsafe endpoint access and the commit message describes the dereference path.

3. **Reachability analysis**

The bug is triggered by a malformed USB device exposing a vendor-specific interface with zero endpoint descriptors. No local account is required on the victim in CVSS-style terms, but the attacker needs physical USB access or a way to emulate a USB device to the host. Namespaces and containers do not materially reduce the required access because the trigger is device enumeration in the host kernel. The affected driver path is not a network path and is not normally exposed to remote attackers. Realistic exploitation is a physical DoS scenario against systems that accept untrusted USB devices.

4. **Severity interpretation**

This behaves like an ordinary Moderate or Low-like kernel issue rather than an Important-class vulnerability. The theoretical impact is a kernel oops or crash from a NULL pointer dereference. There is no evidence of a memory corruption primitive that could support privilege escalation, information disclosure, or integrity compromise. The physical-only reachability strongly limits practical exposure.

5. **One-sentence report phrase**

A malformed physical USB device can trigger a NULL pointer dereference in the ALSA/FCP interface lookup path by exposing a vendor-specific interface without endpoints, causing a local physical denial of service without evidence of privilege escalation or data exposure.

6. **Manual review recommendation**

**NO MANUAL CHECK NEEDED**

This is a physical USB NULL pointer dereference with DoS-only impact, no supported memory corruption primitive beyond invalid dereference, no network reachability, and a low ActionableScore.

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

Patch: ALSA: FCP: Fix NULL pointer dereference in interface lookup [ Upstream
Commit: f28d7b5f1578a7501ab17b10643ed1e4f729187e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f28d7b5f1578a7501ab17b10643ed1e4f729187e

Changed files:
  sound/usb/fcp.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=f28d7b5f1578a7501ab17b10643ed1e4f729187e

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

The original Linux kernel CVE announcement for CVE-2026-72403 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72403

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:N/I:N/A:H
  The Best / paranoid CVSS score: 4.6

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: 0
  Paranoid ActionableScore: 1

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).