[CVE-2026-98482][MODERATE REGULAR] nfc: llcp: drop truncated I/RR/RNR PDUs in nfc_llcp_recv_hdlc()

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

CVE: CVE-2026-98482
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: nfc: llcp: drop truncated I/RR/RNR PDUs in nfc_llcp_recv_hdlc()
Commit: 3afdbebfee2ef7e9510880868cfb482cbffe6836
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3afdbebfee2ef7e9510880868cfb482cbffe6836
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98482
Analysis date: Mon, 19 Oct 2026 06:28:36 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A nearby NFC peer can send a truncated LLCP I, RR, or RNR PDU that causes a one-byte read from uninitialized skb tailroom and may disrupt the current LLCP connection, but no disclosure, kernel write, host crash, or privilege escalation is established.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98482 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98482

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 REGULAR
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-2026-98482	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98482 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE AEGIS_AS=3 LEGACY=MODERATE RESULT=SAME V39_AEGIS_ONE_STEP_UP=LOW->MODERATE (final reconciliation agrees; DECISION: both MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L';CWE-908;*CWE-20;CWE-125;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.4';DESCR 'A truncated NFC LLCP I, RR, or RNR PDU can reach nfc_llcp_recv_hdlc with only the two-byte LLCP header present. The function then reads the missing sequence byte from uninitialized skb tailroom and uses it as N(R) or N(S), which may affect LLCP protocol state and disrupt the current connection. For the CVSS the PR:N value is used because a nearby NFC peer can supply the malformed PDU without an account or local code execution on the target. AV:A is used because exploitation requires NFC proximity or direct access to the adjacent NFC link rather than general Internet reachability. The demonstrated impact is limited availability loss for NFC communication. The paranoid score allows C:L for a possible behavioral side channel based on the uninitialized byte, but there is no demonstrated direct memory disclosure, write primitive, UAF, privilege escalation, or host-wide kernel crash. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.4 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to MODERATE 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 KPANIC_UNSUPPORTED_REMOVED and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 4.3 and ActionableScore 3 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	SIMPLEFIX SKB IMPROVEONLY LINUS KPANIC_UNSUPPORTED_REMOVED V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap changed either score.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +2 Directly network-triggerable. An adjacent NFC peer can deliver a truncated I, RR, or RNR PDU to the vulnerable receive path without local execution or administrative privileges.
* +0 Limited invalid read. The code reads one byte beyond the logical skb length but within uninitialized skb tailroom. No heap OOB write, UAF, or access beyond the underlying allocation is established.
* +0 Protocol-state influence. The uninitialized byte becomes N(R) or N(S), but a peer can already select these values in a valid PDU. This does not establish a new controlled corruption primitive.
* +0 Availability. Disruption of the current LLCP connection is plausible, but no kernel crash, host-wide DoS, persistent outage, or independently strong availability effect is demonstrated.
* +0 Confidentiality. No path returning the uninitialized byte to the peer is established. A hypothetical behavioral oracle is insufficient for a disclosure point.
* +0 Integrity. No write to kernel memory, protected state, shared backing, or another principal's data is demonstrated.

Not awarded:

* NEW52 B5-R does not apply because there is no heap OOB write, retry accumulation, or later consumption of corrupted written state.
* NEW53 B3-PENDING does not apply because there is no write to shared or file-backed storage.
* V33 and V34 do not apply because no attacker-influenced write to active structured state or checksum metadata exists.
* No controlled reclaim, arbitrary write, UAF, authorization bypass, privilege escalation, or security-boundary crossing is established.
* No hardware rarity penalty is applied merely because NFC hardware is required.
* No separate availability point is awarded for possible connection disruption.

3. Reachability analysis

A nearby or directly connected NFC LLCP peer can send the malformed two-byte PDU. The complete trigger does not require host UID 0, a local account, a namespace capability, or host-administrator authority.

The target must have an active NFC LLCP receive path and applicable NFC hardware or transport. This is a deployment prerequisite rather than evidence of a privileged attacker requirement. The trigger is adjacent-network rather than Internet remote.

No user or network namespace operation is needed, so namespace-scoped privilege is not part of the trigger. There is no race or timing requirement. The peer directly controls PDU truncation, but it does not directly control the uninitialized tailroom byte.

4. Primitive and severity interpretation

The exact primitive is a one-byte read from uninitialized skb tailroom beyond the logical packet length. The value is consumed as an LLCP sequence number and can affect processing of the current protocol session.

This is not an actual heap OOB write, UAF, stale-object use, repeated release, or memory-lifetime violation. It is classified as CLASS_C because the demonstrated behavior is an invalid read followed by limited protocol-state processing.

The supported consequence is malformed LLCP session behavior or connection disruption. Information disclosure through observable responses remains speculative, and no host crash or privilege escalation path is supported.

ImportantCandidate is NO because there is no active-state write, shared-backing modification, authorization bypass, or meaningful corruption primitive requiring Important-grade preservation. AutoDowngradeAllowed is YES because the issue remains a constrained adjacent-input validation defect without unresolved kernel-corruption leverage.

5. One-sentence report phrase

A nearby NFC peer can send a truncated LLCP I, RR, or RNR PDU that causes a one-byte read from uninitialized skb tailroom and may disrupt the current LLCP connection, but no disclosure, kernel write, host crash, or privilege escalation is established.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether any observable LLCP response can expose information derived from the uninitialized sequence byte. The supplied evidence does not support mandatory Important-grade review.

7. Call-site confidence

Call-site confidence: high

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

Patch: nfc: llcp: drop truncated I/RR/RNR PDUs in nfc_llcp_recv_hdlc()
Commit: 3afdbebfee2ef7e9510880868cfb482cbffe6836
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3afdbebfee2ef7e9510880868cfb482cbffe6836

Commit description:

nfc_llcp_recv_hdlc() reads the sequence byte skb->data[2], via
nfc_llcp_ns()/nfc_llcp_nr(), before any length check. The receive path
only guarantees the two-byte LLCP header -- __nfc_llcp_recv() checks it
with pskb_may_pull() and nfc_llcp_recv_agf() admits two-byte inner PDUs
-- so a two-byte I, RR or RNR PDU reads one byte of uninitialised skb
tailroom. The byte becomes N(R)/N(S); a peer can already set those with
a well-formed PDU, so this is acting on uninitialised memory, not new
peer control.

Guard the read with pskb_may_pull(), as commit 95674f5 ("nfc: llcp:
reject PDUs shorter than the LLCP header") did for the two-byte header,
so the sequence byte is present and linear before it is read. RR and RNR
PDUs are LLCP_HEADER_SIZE + LLCP_SEQUENCE_SIZE bytes and an I PDU is
longer, so no valid frame is rejected; a truncated PDU is malformed, so
return without a DM reply.

Fixes: d646960 ("NFC: Initial LLCP support")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Aamir Ahmed <elb12345@hotmail.co.uk>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/AS8P251MB0001789BBF04B72745C7D96BC8BA2@AS8P251MB0001.EURP251.PROD.OUTLOOK.COM
Signed-off-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/nfc/llcp_core.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=3afdbebfee2ef7e9510880868cfb482cbffe6836

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

The original Linux kernel CVE announcement for CVE-2026-98482 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98482

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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS score: 5.4

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: unknown
  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: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).