[CVE-2026-63958][MODERATE 7.0] usb: typec: ucsi: validate connector number in ucsi_connector_change()

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

CVE: CVE-2026-63958
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: usb: typec: ucsi: validate connector number in ucsi_connector_change()
Commit: cea949203faef9cb783adc7b978cce056271e057
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cea949203faef9cb783adc7b978cce056271e057
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63958
Analysis date: Sun, 19 Jul 2026 18:36:50 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious or buggy UCSI PPM can supply an invalid connector number that makes `ucsi_connector_change()` schedule work on memory past the connector array, causing a likely kernel crash and a constrained memory-corruption risk.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-63958 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63958

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-2026-63958	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-129;*CWE-787;*CWE-20;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.4';DESCR 'A UCSI connector change notification can carry an invalid 7-bit connector number supplied by the PPM. ucsi_connector_change used that value to index the connector array before checking it against cap.num_connectors, so a buggy or malicious PPM could make the kernel operate on memory past the end of the array. The dangerous operation is schedule_work on an out-of-bounds work item, which can lead to kernel memory corruption or a crash. For the CVSS the PR:N is used because a malicious or compromised PPM can supply the invalid connector number without a local user account on the host. The issue is not network reachable and is mainly relevant to systems where EC firmware or an attached UCSI controller can emit malformed CCI notifications. Impact is at least local or physical denial of service and in the paranoid case may include confidentiality and integrity impact due to memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 6)	YES	USB SIMPLEFIX  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	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

* Firmware-mediated external influence: +1. The connector number is supplied by the PPM, including EC firmware or an attached UCSI controller.
* Memory corruption, weak/indirect corruption candidate: +1. The unchecked connector number is used as an array index and can produce an out-of-bounds `struct ucsi_connector` pointer.
* Weak LPE concern: +1. `schedule_work()` is called on an out-of-bounds `work_struct`, which is a corruption sink, but no controlled reclaim, controlled payload, or reliable object replacement is shown.
* Reliable kernel crash / strong DoS: +1. Scheduling work on memory past the connector array is likely to cause a crash or workqueue corruption.
* Privileged kernel/device-management memory corruption path: +1. The bug is in a trusted USB Type-C UCSI device-management path fed by firmware/controller notifications.
* Broad/default/common subsystem exposure: +1. UCSI is common on modern USB Type-C systems, although the malicious input source is platform-specific.
* Corruption primitive highly constrained: -1. The attacker influence is mainly the connector number. The target is adjacent kernel memory selected indirectly, not an arbitrary attacker-chosen address or payload.

Paranoid-only adjustment:

* Confidentiality/integrity impact plausible: +1 effective uplift. Because an out-of-bounds `work_struct` may corrupt kernel workqueue state, limited C/I risk is defensible for manual-review triage, but the score is kept below Important because no concrete exploit primitive is demonstrated.

## 3. Reachability analysis

The bug is not network reachable and is not normally triggerable by an unprivileged local user. The realistic trigger is a buggy or malicious PPM, EC firmware, or an attached UCSI controller on transports such as ccg, stm32g0, or glink. Namespaces and containers do not meaningfully lower the privilege requirement because the malformed connector-change notification comes from firmware or device-side control, not from a normal container-visible API. The path may be active by default on systems using UCSI for USB Type-C management, but exploitation requires control over or compromise of the firmware/controller notification source.

Call-site confidence: high. The patch shows the unchecked index and the immediate use of `schedule_work(&con->work)` on the derived object.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because the patch prevents an out-of-bounds object selection followed by workqueue scheduling on memory past the array. It is not a clean Important by default because the primitive is firmware-mediated, constrained, and lacks evidence of attacker-controlled payload, reclaim, arbitrary write, or demonstrated LPE. Conservative handling is Actionable Moderate. Paranoid handling remains Actionable Moderate at minimum and should not be auto-closed because the bug is a kernel memory-corruption candidate in a privileged device-management path.

## 5. One-sentence report phrase

A malicious or buggy UCSI PPM can supply an invalid connector number that makes `ucsi_connector_change()` schedule work on memory past the connector array, causing a likely kernel crash and a constrained memory-corruption risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch directly fixes an unchecked firmware-supplied array index followed by `schedule_work()` on an out-of-bounds object, making this a constrained but real kernel memory-corruption candidate rather than a pure validation-only or DoS-only issue.

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

Patch: usb: typec: ucsi: validate connector number in ucsi_connector_change()
Commit: cea949203faef9cb783adc7b978cce056271e057
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cea949203faef9cb783adc7b978cce056271e057

Commit description:

The connector number in a UCSI CCI notification is a 7-bit field
supplied by the PPM.  ucsi_connector_change() uses it to index the
ucsi->connector[] array without checking it against the number of
connectors the PPM reported at init time, so a buggy or malicious PPM
(EC firmware, or an I2C-attached UCSI controller on the ccg / stm32g0 /
glink transports) can drive schedule_work() on memory past the end of
the array.

Reject connector numbers that are zero or exceed cap.num_connectors
before dereferencing the array.

Assisted-by: gkh_clanker_t1000
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Benson Leung <bleung@chromium.org>
Cc: Jameson Thies <jthies@google.com>
Cc: Nathan Rebello <nathan.c.rebello@gmail.com>
Cc: Johan Hovold <johan@kernel.org>
Cc: Pooja Katiyar <pooja.katiyar@intel.com>
Cc: Hsin-Te Yuan <yuanhsinte@chromium.org>
Cc: Abel Vesa <abelvesa@kernel.org>
Cc: stable <stable@kernel.org>
Reviewed-by: Abel Vesa <abel.vesa@oss.qualcomm.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Benson Leung <bleung@chromium.org>
Link: https://patch.msgid.link/2026051351-truck-steadfast-df48@gregkh
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/typec/ucsi/ucsi.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=cea949203faef9cb783adc7b978cce056271e057

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

The original Linux kernel CVE announcement for CVE-2026-63958 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63958

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:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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).