[CVE-2026-63962][IMPORTANT] usb: typec: tcpm: bound altmode_desc[] per iteration in svdm_consume_modes()

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

CVE: CVE-2026-63962
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: usb: typec: tcpm: bound altmode_desc[] per iteration in svdm_consume_modes()
Commit: 845598b154b9a92e9d279fafafa9405c121ae805
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=845598b154b9a92e9d279fafafa9405c121ae805
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63962
Analysis date: Sun, 19 Jul 2026 13:35:22 -0400
ActionableScore: 8
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious USB Type C PD partner can send crafted or unsolicited Discover Modes ACK messages that cause `svdm_consume_modes()` to write past `altmode_desc[]`, corrupting adjacent TCPM kernel state and potentially causing DoS or stronger memory-corruption impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-63962 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63962

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: IMPORTANT
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-2026-63962	IMPORTANT	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-129;*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 'An out of bounds write in the USB Type C TCPM SVDM mode handling can occur because svdm_consume_modes validates the altmode_desc bound before the loop but not for each VDO consumed inside the loop. A malicious USB Type C PD partner can send unsolicited Discover Modes ACK messages after the partner object exists and can drive the altmodes counter near ALTMODE_DISCOVERY_MAX before sending one extra response with multiple VDO values. This can write past the altmode_desc array and corrupt adjacent TCPM state such as a partner_altmode pointer array with partner controlled SVID/VDO data. For the CVSS the PR:N is used because the attacker does not need an account or local privileges on the target once a malicious or compromised USB Type C PD partner can communicate over the physical connection. The issue is not network reachable and requires physical USB Type C attachment or an equivalent malicious dock or port partner. Impact is at least denial of service and in the worst case may allow confidentiality and integrity impact due to kernel memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE USB NETWORK KPANIC 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated or external device influence: +1
  A malicious USB Type C PD partner can send crafted SVDM Discover Modes ACK messages over the physical Type C connection.

* Memory corruption, strong corruption primitive: +2
  The bug is an out of bounds write past `altmode_desc[]`.

* Weak LPE concern: +1
  The write can corrupt adjacent TCPM state, including a pointer array, but the patch does not demonstrate a full reclaim, arbitrary write, callback control, or reliable exploit primitive.

* Reliable kernel crash / strong DoS: +1
  Kernel memory corruption in a Type C state machine is a realistic crash vector.

* Privileged kernel/device-management memory corruption path: +1
  The corruption occurs in trusted USB Type C TCPM kernel state driven by an external device protocol.

* Broad/common hardware exposure: +1
  USB Type C TCPM is relevant to many laptops, mobile, embedded, and dock-capable systems.

* Physical-only condition: -2
  The attacker generally needs physical attachment or control of a connected malicious dock or Type C PD partner.

Paranoid additions/changes:

* Stronger LPE plausibility: +2 instead of +1
  The overwrite reaches adjacent pointer-array state with partner-influenced data, so manual review should treat this as potentially exploitable kernel memory corruption.

* Confidentiality impact plausible: +1
  If pointer corruption can be shaped into object confusion or controlled dereference, information exposure is possible.

* Integrity impact plausible: +1
  Kernel pointer/state corruption can plausibly affect integrity in a worst-case exploitation model.

## 3. Reachability analysis

The bug is triggerable by a malicious or broken USB Type C PD partner, such as a hostile cable, dock, charger, peripheral, or device connected to the target Type C port. It is not network reachable and does not require a local user account on the victim. Namespaces and containers do not materially affect reachability because the attack path is below userspace privilege boundaries and enters through the USB Type C PD protocol handling path. Realistic exploitation requires hardware presence and a vulnerable TCPM-controlled Type C port, but the trigger logic described in the commit is concrete: unsolicited Discover Modes ACK messages can be consumed once `port->partner` exists.

## 4. Severity interpretation

This is not an ordinary Moderate correctness bug. The patch fixes an attacker-influenced kernel out of bounds write, not just a warning or bounds cleanup. Realistic exploitation is limited by physical access and by the need to shape Type C PD messages, so the conservative score stays in Actionable Moderate territory. The paranoid score reaches Strong Important candidate because the overwrite can extend past `altmode_desc[]` into adjacent pointer-array state, which is the kind of primitive that needs manual kernel memory corruption review.

## 5. One-sentence report phrase

A malicious USB Type C PD partner can send crafted or unsolicited Discover Modes ACK messages that cause `svdm_consume_modes()` to write past `altmode_desc[]`, corrupting adjacent TCPM kernel state and potentially causing DoS or stronger memory-corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is a concrete OOB write in kernel memory with attacker-influenced protocol data and adjacent pointer-array corruption, even though exploitation is physical/local-device mediated rather than network remote.

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UPSTREAM PATCH SUMMARY
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Patch: usb: typec: tcpm: bound altmode_desc[] per iteration in svdm_consume_modes()
Commit: 845598b154b9a92e9d279fafafa9405c121ae805
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=845598b154b9a92e9d279fafafa9405c121ae805

Commit description:

svdm_consume_modes() checks pmdata->altmodes against the array size once
before the loop over the count, but forgot to check the bound at every
point in the loop.

In the well-behaved SVDM discovery flow this is harmless because each of
at most SVID_DISCOVERY_MAX SVIDs contributes at most MODE_DISCOVERY_MAX
modes, exactly filling altmode_desc[ALTMODE_DISCOVERY_MAX].  But the
CMDT_RSP_ACK handler in tcpm_pd_svdm() does not correlate an incoming
ACK with any request the port actually sent.  Once port->partner is set,
an unsolicited Discover Modes ACK is consumed unconditionally.  A broken
or malicious port partner can therefore drive altmodes to
ALTMODE_DISCOVERY_MAX - 1 via the normal flow, and then send one extra
Discover Modes ACK with seven VDOs.  Because the pre-loop check passes,
the loop could then writes up to five entries past altmode_desc[].  For
mode_data_prime the next field in struct tcpm_port is the
partner_altmode[] pointer array, which then receives partner-chosen
SVID/VDO bytes.

Move the bound check inside the loop so the array can never be indexed
past ALTMODE_DISCOVERY_MAX regardless of how many VDOs the partner
supplies or how the function was reached.

Assisted-by: gkh_clanker_t1000
Cc: Badhri Jagan Sridharan <badhri@google.com>
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: stable <stable@kernel.org>
Link: https://patch.msgid.link/2026051351-reshuffle-skillful-90af@gregkh
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/typec/tcpm/tcpm.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=845598b154b9a92e9d279fafafa9405c121ae805

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

The original Linux kernel CVE announcement for CVE-2026-63962 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63962

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: 8

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).