* [CVE-2026-98600][MODERATE REGULAR] Bluetooth: RFCOMM: Reject short EA=0 frames in rfcomm_recv_frame() [ Upstream
@ 2026-10-24 15:52 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-24 15:52 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98600
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: RFCOMM: Reject short EA=0 frames in rfcomm_recv_frame() [ Upstream
Commit: 76876fd26569302d26d91cbe8b75fa8e66cf8969
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=76876fd26569302d26d91cbe8b75fa8e66cf8969
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98600
Analysis date: Sat, 24 Oct 2026 11:52:10 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
A short EA=0 RFCOMM frame can leave its header unconsumed and cause bounded payload or multiplexer-command misinterpretation without demonstrated kernel memory corruption.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98600 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98600
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: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98600 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98600 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=MODERATE RESULT=SAME (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:N/I:L/A:L';*CWE-20;CWE-130;CWE-252;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.4';DESCR 'RFCOMM accepted a four byte frame with EA equal to zero even though the extended length form requires at least a four byte header and one byte FCS. After FCS removal skb_pull failed safely and left the header at skb data, but its ignored return value allowed those bytes to be queued as application payload or parsed as a DLCI 0 multiplexer control command. This is a protocol validation and data confusion issue rather than demonstrated memory corruption. For the CVSS the PR:N value is selected because a nearby Bluetooth peer can supply the malformed frame without obtaining privileges on the target, although pairing and service policy may restrict practical reachability. The grounded impact is limited RFCOMM session disruption, while the worst case includes low integrity impact from unintended payload or control command interpretation. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 5.4 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. 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. KP and FD specialist checks stage MODERATE_KPANIC to MODERATE because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. 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_FALSEPOSCHECKOFKP. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE REMOTE SIMPLEFIX NETWORK SKB LINUS MEMORY LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 4.
* Conservative score: 4; no floor or cap applied.
* Raw paranoid score: 4.
* Paranoid score: 4; stronger confidentiality, integrity, or memory-corruption effects are not sufficiently evidenced.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +2 adjacent network reachability: a Bluetooth RFCOMM peer can supply the malformed frame without local target privileges, subject to connection/pairing policy.
* +1 weak semantic confusion: after failed `skb_pull(skb, 4)`, the unchanged three-byte RFCOMM header can be consumed under payload or MCC-command semantics.
* +1 limited availability concern: malformed control/data interpretation can plausibly disrupt the RFCOMM session.
* No OOB access or kernel-memory write: `skb_pull()` fails safely and does not advance `skb->data`.
* No strong semantic-reinterpretation bonus: later parsing is shown, but successful execution of a security-sensitive MCC operation is not.
* No integrity bonus: unintended application bytes or MCC parsing is plausible, but no protected state change is established.
* No kernel-crash bonus, disclosure, authorization bypass, UAF, arbitrary write, or persistent resource effect is shown.
* B5-R and B3-PENDING do not apply because there is no heap OOB write or shared-backing write.
3. Reachability analysis
A connected nearby Bluetooth peer can form the short EA=0 RFCOMM frame. This supports below-host-admin triggering and no host UID 0 requirement. Pairing, service exposure, and RFCOMM session policy may restrict practical access, but they do not establish a privileged local prerequisite. No namespace capability, prior host configuration, special hardware beyond Bluetooth support, or timing race is demonstrated.
4. Primitive and severity reading
The primitive is bounded protocol-state confusion: a failed pull leaves header bytes in place, after which they may be queued as application data or passed to the MCC parser. It is neither a UAF nor memory corruption. The shown effect is malformed session processing and possible session disruption; execution of a meaningful control command or modification of protected state remains unproven. This is therefore CLASS_C, not an Important-preserving Class A/B primitive. Auto-downgrade remains allowed, though review is advisable to verify reachable MCC handlers.
5. One-sentence report phrase
A short EA=0 RFCOMM frame can leave its header unconsumed and cause bounded payload or multiplexer-command misinterpretation without demonstrated kernel memory corruption.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm whether the three retained header bytes can form any accepted MCC command with effects beyond RFCOMM session disruption.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: Bluetooth: RFCOMM: Reject short EA=0 frames in rfcomm_recv_frame() [ Upstream
Commit: 76876fd26569302d26d91cbe8b75fa8e66cf8969
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=76876fd26569302d26d91cbe8b75fa8e66cf8969
Changed files:
net/bluetooth/rfcomm/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=76876fd26569302d26d91cbe8b75fa8e66cf8969
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98600 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98600
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:N/I:L/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: 4
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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