* [CVE-2026-98582][MODERATE REGULAR] nfc: st21nfca: validate received frame size [ Upstream
@ 2026-10-19 3:25 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-19 3:25 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98582
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: nfc: st21nfca: validate received frame size [ Upstream
Commit: 8934d2889ae16a7c77520e002398d0689c1ecea5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8934d2889ae16a7c77520e002398d0689c1ecea5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98582
Analysis date: Sun, 18 Oct 2026 23:25:41 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A malformed ST21NFCA receive frame can cause out-of-bounds reads during byte unstuffing or CRC validation, potentially resulting in a kernel warning or denial of service, while practical NFC peer reachability depends on controller firmware behavior.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98582 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98582
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98582 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98582 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF V39_AEGIS_ONE_STEP_UP=LOW->MODERATE TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H';CWE-125;*CWE-20;CWE-193;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.9';DESCR 'st21nfca_hci_i2c_repack() can process a received frame that is too short for CRC validation or ends with an escape marker without an encoded byte. The first case can make check_crc() read outside the valid frame data. The second case can make the byte unstuffing loop read one byte beyond the current skb length. The demonstrated primitive is an out-of-bounds read with a plausible kernel crash or warning, while no out-of-bounds write or UAF is shown. For the CVSS the PR:N value is used because an adjacent NFC peer would not need an account or privileges on the target if malformed transport framing can be influenced through the radio path. AV:A and AC:H reflect the need for proximity and the uncertainty that the NFC controller exposes attacker-controlled SOF, EOF, and byte stuffing to the host driver. Impact is primarily denial of service. Limited confidentiality impact is retained only in the paranoid score because data outside the logical frame boundary is read, but no direct disclosure channel is established. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.9 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 3.3 and ActionableScore 2 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE_KPANIC. 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 USB SKB LINUS KPANIC_UNSUPPORTED_REMOVED V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
Conservative signals:
* +1 Reliable kernel crash or strong DoS concern. A malformed frame can leave fewer bytes than `check_crc()` requires or can cause the unstuffing loop to read beyond the current skb length. Depending on allocation layout and kernel hardening, this can produce a fault, KASAN report, warning, or kernel crash.
* +0 Limited OOB read. The patch establishes reads outside the valid frame boundary, but no bytes are copied to userspace, the network peer, or another observable output.
* +0 No write primitive. The unstuffing assignments use a write cursor that does not advance beyond the number of consumed input bytes. The defect is an invalid source read, not an established heap OOB write.
Additional paranoid signal:
* +1 Firmware-mediated external influence. An NFC peer may influence data delivered through the controller, but the controller and its firmware mediate the I2C transport framing. Direct control over SOF, EOF, and byte-stuffing markers from the radio side remains unresolved.
Important non-awarded signals:
* No UAF, stale lifetime operation, double release, or refcount mutation is established.
* No OOB write, arbitrary write, controlled reclaim, callback influence, or active structured-state corruption is established.
* Confidentiality is not awarded because no disclosure path for the out-of-frame bytes is shown.
* Integrity is not awarded because the malformed frame is rejected or consumed only for CRC validation and no protected state modification is shown.
* Direct remote reachability is not established because firmware mediation is material.
* An additional availability point is not awarded because it would duplicate the same possible crash.
* NEW52 B5-R does not apply. There is no retry-accumulated heap OOB write, retry-controlled offset, or later consumption of corrupted structured state.
* NEW53 B3-PENDING does not apply. No shared or file-backed page modification is present.
* V33 and V34 do not apply. No attacker-influenced write into active structured state and no privileged downstream consumer of corrupted metadata are established.
* V32 does not apply. This is not a checksum-placement or `CHECKSUM_PARTIAL` metadata write.
* B4-PENDING does not apply. There is no authorization decision or DENY-to-ALLOW transition.
3. Reachability analysis
The vulnerable function processes frames received from an ST21NFCA NFC controller over I2C. A nearby NFC peer is a plausible source of malformed higher-level input, but the supplied evidence does not establish that the peer can directly control the low-level SOF, EOF, escape-marker, and byte-stuffing representation observed by this driver.
If the controller forwards or constructs such malformed transport framing from radio-controlled input, no host account or host privilege would be required. If the controller validates or independently generates the framing, practical triggering may instead require faulty firmware, a compromised controller, or physical influence over the I2C path. Therefore the complete privilege boundary remains unresolved and `HostAdminRequired=UNKNOWN`.
No namespace or capability-controlled interface is involved, so `NamespaceScopedPrivilege=NO`. Specialized ST21NFCA hardware and its driver are prerequisites. There is no race or timing requirement.
4. Primitive and severity interpretation
The exact primitive is a limited out-of-bounds read from an skb-backed frame:
1. A premature EOF can leave insufficient bytes for LLC and CRC processing.
2. A trailing escape marker can make the old loop read the missing encoded byte beyond `skb->len`.
This is fixed receive-buffer storage rather than an active structured-object lifetime violation. There is no post-lifetime object use, no repeated release, and no evidence that the invalidly read byte controls a subsequent privileged write or security decision.
`PrimitiveClass=CLASS_C` because the demonstrated behavior is malformed-input processing with an invalid read and possible crash, without an independently useful corruption primitive. The practical consequence is denial of service if the read reaches inaccessible memory or triggers a fatal diagnostic. Information disclosure, privilege escalation, and persistent integrity modification are not supported.
`ImportantCandidate=NO` because neither Class A nor a strong unresolved Class B primitive exists. `AutoDowngradeAllowed=YES` because the issue remains a constrained read-only boundary violation with no established disclosure, write, lifetime corruption, or security-boundary bypass.
5. One-sentence report phrase
A malformed ST21NFCA receive frame can cause out-of-bounds reads during byte unstuffing or CRC validation, potentially resulting in a kernel warning or denial of service, while practical NFC peer reachability depends on controller firmware behavior.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Confirm whether an adjacent NFC peer can influence the I2C-level EOF and escape-marker framing delivered by the controller. This determines whether the issue is externally reachable or limited to malformed controller or physical-bus input.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: nfc: st21nfca: validate received frame size [ Upstream
Commit: 8934d2889ae16a7c77520e002398d0689c1ecea5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8934d2889ae16a7c77520e002398d0689c1ecea5
Changed files:
drivers/nfc/st21nfca/i2c.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=8934d2889ae16a7c77520e002398d0689c1ecea5
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98582 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98582
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:H/PR:N/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H
The Best / paranoid CVSS score: 5.9
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: 1
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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