[CVE-2026-98761][LOW] usb: typec: tcpm: recover after failure to start the frs ams

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

CVE: CVE-2026-98761
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: usb: typec: tcpm: recover after failure to start the frs ams
Commit: 184d842121e7d1fbc3a81895f36f72fa27444163
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=184d842121e7d1fbc3a81895f36f72fa27444163
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98761
Analysis date: Sat, 24 Oct 2026 04:51:07 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A physically triggered failed FRS transition can leave USB-C VBUS enabled after disconnect because the TCPM state machine omits error recovery.

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

The original Linux kernel CVE announcement for CVE-2026-98761 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98761

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
======================================================================

CVE-2026-98761	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98761 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=LOW RESULT=DIFF (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-754;CWE-404;CWE-459;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.2';DESCR 'A logic and incomplete recovery flaw occurs when FAST_ROLE_SWAP AMS cannot start after an anomalous FRS signal during cable disconnection. The TCPC may already have started sourcing VBUS, while the EAGAIN path only selects INVALID_STATE and does not reset the port, allowing VBUS to remain enabled after disconnect. This can affect USB Type C port availability and may create power contention, but no invalid memory access, information leak, or memory write primitive is shown. For the CVSS the PR:N value is used because no authenticated software privilege is required, although reliable triggering requires physical access and a cable or partner capable of producing an anomalous FRS signal during disconnect. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 4.2 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage IMPORTANT to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 2.0 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	REMOTE DANGER USB NETWORK LINUS LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED	-	-	checked

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

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: -1 (+1 device-port availability impact, -2 physical trigger requirement).
* Conservative score: 0, applying the score-range lower bound.
* Raw paranoid score: -1; no technically supported additional effect.
* Paranoid score: 0, applying the score-range lower bound.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1: Device-local availability impact. Failure recovery leaves VBUS sourcing enabled after cable disconnection and may leave the Type-C port in an invalid operational state.
* -2: Physical-only trigger. The evidenced trigger is an anomalous FRS signal from a cable or attached partner during physical disconnection.
* No memory corruption, UAF, OOB access, persistent kernel-resource leak, authorization bypass, host-wide crash, or protected-state corruption is shown.
* B5-R does not apply: there is no heap OOB write, retry-accumulated index, or later consumption of corrupted structured memory.
* B3-PENDING does not apply: no shared/file-backed storage write exists.
* B4-PENDING does not apply: the patch changes state-machine recovery, not a DENY-to-ALLOW authorization decision.

3. Reachability analysis

A physically connected cable or partner that incorrectly emits an FRS signal during disconnect can trigger the condition without host software privileges or UID 0. No namespace capability, prior privileged software setup, ioctl path, or remotely reachable packet path is involved. Timing depends on the anomalous signal coinciding with disconnection, but no separate race penalty is applied because physical access already captures the principal restriction.

4. Primitive and severity reading

The exact defect is incomplete Type-C state-machine recovery: `-EAGAIN` from `tcpm_ams_start()` previously selected `INVALID_STATE` rather than initiating `ERROR_RECOVERY`, allowing autonomously enabled VBUS sourcing to remain on. This is device/power-state mismanagement, not kernel memory or authorization corruption. The shown consequence is port disruption and possible power contention; host panic, hardware damage, persistent system-wide denial of service, and attacker-controlled writes are unproven. Therefore the primitive class is NONE, no Important review candidate exists, and automatic downgrade is allowed.

5. One-sentence report phrase

A physically triggered failed FRS transition can leave USB-C VBUS enabled after disconnect because the TCPM state machine omits error recovery.

6. Manual review advice

NO MANUAL CHECK NEEDED

The patch supports only a physically triggered, device-local recovery and availability defect without a security primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: usb: typec: tcpm: recover after failure to start the frs ams
Commit: 184d842121e7d1fbc3a81895f36f72fa27444163
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=184d842121e7d1fbc3a81895f36f72fa27444163

Commit description:

Reset the port if the tcpm fails to start the FAST_ROLE_SWAP AMS by
initiating error recovery on it.

This helps in cases where some cables (incorrectly) signal an FRS to
an FRS capable port during disconnection. The TCPC autonomously starts
sourcing VBUS on detecting the FRS signal. However, the VBUS sourcing is
left on when the FAST_ROLE_SWAP AMS fails to start (as tcpm_sink_tx_ok
is 0 as CC is open due to the cable disconnect). This is because the
code sets the state to INVALID_STATE without resetting the port state.

Log snippet before changes:
[  101.401960] AMS FAST_ROLE_SWAP start
[  101.401971] Sink TX No Go
[  101.401982] sourcing vbus
[  101.401987] VBUS on
[  101.402159] VBUS on
[  109.257809] CC1: 0 -> 0, CC2: 5 -> 0 [state SNK_READY, polarity 1, disconnected]
[  111.267442] VBUS on

After changes:
[   70.541211] AMS FAST_ROLE_SWAP start
[   70.541220] Sink TX No Go
[   70.541228] state change SNK_READY -> ERROR_RECOVERY [rev3 NONE_AMS]
[   70.541362] VBUS on
[   70.541365] sourcing vbus
[   70.541367] VBUS on
[   70.541374] state change ERROR_RECOVERY -> PORT_RESET [rev3 NONE_AMS]
[   70.541410] disable vbus discharge ret:0
[   70.543028] Setting usb_comm capable false
[   70.544009] Setting voltage/current limit 0 mV 0 mA
[   70.544034] polarity 0
[   70.544239] Requesting mux state 0, usb-role 0, orientation 0
[   70.555550] cc:=0
[   70.555595] pending state change PORT_RESET -> PORT_RESET_WAIT_OFF @ 100 ms [rev3 NONE_AMS]
[   70.555697] VBUS off
[   70.555702] VBUS VSAFE0V
[   70.555762] CC1: 5 -> 0, CC2: 0 -> 0 [state PORT_RESET, polarity 0, disconnected]
[   70.587794] VBUS off
[   70.587799] VBUS VSAFE0V
[   70.655672] state change PORT_RESET -> PORT_RESET_WAIT_OFF [delayed 100 ms]
[   70.655682] state change PORT_RESET_WAIT_OFF -> SNK_UNATTACHED [rev3 NONE_AMS]
[   70.655686] Start toggling
[   70.656274] CC1: 0 -> 0, CC2: 0 -> 0 [state TOGGLING, polarity 0, disconnected]

Fixes: 0908c5a ("usb: typec: tcpm: AMS and Collision Avoidance")
Cc: stable <stable@kernel.org>
Signed-off-by: Amit Sunil Dhamne <amitsd@google.com>
Reviewed-by: Badhri Jagan Sridharan <badhri@google.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://patch.msgid.link/20260903-frs-error-handling-v1-1-ad0fee541847@google.com
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=184d842121e7d1fbc3a81895f36f72fa27444163

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

The original Linux kernel CVE announcement for CVE-2026-98761 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98761

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.2

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: unknown
  Paranoid ActionableScore: 0

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).