* [CVE-2026-98902][LOW] md/raid5: let stripe batch bm_seq comparison wrap-safe [ Upstream
@ 2026-10-26 23:16 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-26 23:16 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98902
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: md/raid5: let stripe batch bm_seq comparison wrap-safe [ Upstream
Commit: 647c7289a3960118e249c0a53da6f1ebba1e47a3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=647c7289a3960118e249c0a53da6f1ebba1e47a3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98902
Analysis date: Mon, 26 Oct 2026 19:16:51 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A wraparound-unsafe RAID5 bitmap sequence comparison can preserve stale batching order, with possible recovery inconsistency but no demonstrated memory corruption or protected-data impact.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98902 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98902
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98902 LOW https://www.kernelcve.org/list/?q=CVE-2026-98902 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=0 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:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L';CWE-190;CWE-682;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.3';DESCR 'This is a logic bug in RAID5 bitmap sequence ordering rather than a memory corruption issue. After the 32 bit bm_seq counter wraps, a direct greater than comparison can treat an older pre wrap value as newer and preserve the wrong sequence on a stripe batch head. The demonstrated primitive is incorrect bitmap ordering with no OOB access, UAF, arbitrary write, or information disclosure. For the CVSS the PR:L value reflects that a local process normally needs write access to data backed by the affected MD RAID5 array to contribute the required workload. AC:H reflects the 4294967296 sequence wrap and the additional batching and failure timing needed for a security relevant result. Confidentiality is N. Integrity is L in the base case and H in the paranoid case because incorrect bitmap ordering may affect crash or failure recovery and could theoretically cause persistent data inconsistency. Availability is L because recovery disruption is plausible but host wide failure is not established. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 5.3 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to LOW because the CVSS score, vector or bug class 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 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH and KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 3.1 and ActionableScore 0 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE DISK SIMPLEFIX LINUS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 1.
* Conservative score: 1; no floor or cap applied.
* Raw paranoid score: 1.
* Paranoid score: 1; persistent data corruption is plausible but not sufficiently shown for another point.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Important storage path: `bm_seq` controls RAID5 bitmap/stripe batching state relevant to write ordering and recovery.
* +0 Passive invalid-state concern: the direct comparison mishandles 32-bit wraparound and may retain the wrong sequence, but this is not a separately scored memory-corruption primitive.
* No OOB write, UAF, arbitrary write, disclosure, authorization bypass, or concrete crash is shown.
* No Integrity point: the patch does not establish unauthorized modification of protected data or a specific persistent inconsistency.
* No Availability point: recovery disruption or host failure is not demonstrated.
* No timing penalty: wraparound is required, but the evidence does not prove a narrow or unreliable race.
3. Reachability analysis
A process with write access to data on the affected MD RAID5 array may contribute workload, but the supplied source does not establish who can drive `bm_seq` through wraparound, force the relevant batching state, or produce a security-relevant recovery outcome. The complete trigger’s privilege requirements are therefore unknown. No namespace capability, special hardware, or authorization interface is shown.
4. Primitive and severity reading
The exact defect is signed wraparound-unsafe ordering of active RAID bitmap sequence metadata. The fix changes the comparison to subtraction-based serial ordering. This is passive structured-state inconsistency, classified CLASS_C, not heap corruption or a lifetime violation. A later data/recovery integrity effect is conceivable but unproven. NEW52/B5-R does not apply because there is no heap OOB write, retry-accumulated index, or later consumption of corrupted heap state. ImportantCandidate is NO and automatic Moderate downgrade remains permissible.
5. One-sentence report phrase
A wraparound-unsafe RAID5 bitmap sequence comparison can preserve stale batching order, with possible recovery inconsistency but no demonstrated memory corruption or protected-data impact.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm how `bm_seq` advances and whether stale sequence retention can omit required bitmap persistence or corrupt recovery-visible data.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: md/raid5: let stripe batch bm_seq comparison wrap-safe [ Upstream
Commit: 647c7289a3960118e249c0a53da6f1ebba1e47a3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=647c7289a3960118e249c0a53da6f1ebba1e47a3
Changed files:
drivers/md/raid5.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=647c7289a3960118e249c0a53da6f1ebba1e47a3
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98902 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98902
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:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L
The Best / paranoid CVSS score: 5.3
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: 1
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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