* [CVE-2026-99101][MODERATE REGULAR] ntfs: move attribute payload before shrinking its record [ Upstream
@ 2026-10-29 2:47 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-29 2:47 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99101
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ntfs: move attribute payload before shrinking its record [ Upstream
Commit: 7dc2c524608039d1b082a0087f7aa0751edd4ffb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7dc2c524608039d1b082a0087f7aa0751edd4ffb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99101
Analysis date: Wed, 28 Oct 2026 22:47:37 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
A permitted NTFS attribute-flag transition can persist malformed mapping pairs by shrinking the record before moving its payload, without evidence of kernel OOB corruption or authorization bypass.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99101 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99101
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-2026-99101 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99101 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: LOW) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L';CWE-696;CWE-682;*CWE-664;BEST CVSS score: '4.4';DESCR 'The bug is an incorrect operation order in ntfs_new_attr_flags rather than demonstrated kernel memory corruption. Shrinking the non resident attribute record first can overwrite the old payload with the following attribute, after which memmove persists unrelated bytes as malformed mapping pairs. For the CVSS the PR:L value reflects that a local user normally needs permission to modify compression or sparse flags on a file. The demonstrated impact is limited integrity and availability loss for filesystem metadata or the affected file. There is no supported OOB, UAF, information disclosure, privilege escalation, or direct network trigger. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.4 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 ActionableScore thresholds stage LOW to MODERATE_KPANIC because the ActionableScore 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 INCREASED_FROM_LOW_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN3 and DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';NO MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE DISK LEAK INCREASED_FROM_LOW_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN3 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; no technically supported stronger primitive.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +1 Local unprivileged trigger: a file owner with permission to change compression/sparse flags can plausibly invoke the operation without host-administrator powers.
* +1 Filesystem metadata corruption: incorrect ordering copies bytes from the following attribute and persists them as malformed mapping pairs.
* +1 Important filesystem path: NTFS attribute-record and mapping-pair consistency governs persistent file allocation metadata.
* +1 Practical corruption chain: flag transition → premature record shrink → source payload overwritten → unrelated bytes copied and persisted.
* No OOB write, UAF, arbitrary write, controlled target, disclosure, authorization bypass, kernel crash, or cross-file ownership violation is shown.
* No integrity-impact bonus: corruption of an attacker-authorized file is shown, but unauthorized modification of another principal’s data or protected metadata is not.
* NEW52/B5-R does not apply: there is no retry-accumulated index or confirmed heap OOB write.
* NEW53/B3-PENDING does not apply: no shared/file-backed backing-page isolation failure is shown.
3. Reachability analysis
The plausible attacker is a local file owner or otherwise authorized process changing NTFS compression/sparse state. Host UID 0 and host-admin-equivalent capability are not required by the supplied semantics. No namespace-specific capability chain, special hardware, prior privileged setup, or race is evidenced.
4. Primitive and severity reading
The primitive is an operation-ordering error causing persistent malformed NTFS mapping-pair metadata. It is bounded record-content corruption rather than demonstrated kernel-memory corruption. The later confirmed consumer is ntfsck, which reports an invalid or missing run length; unsafe later kernel consumption, filesystem shutdown, cross-file corruption, or privilege escalation is not established. This supports CLASS_C, not an Important-preserving Class A/B primitive. Auto-downgrade remains allowed because no unresolved ownership or security-boundary primitive is shown.
5. One-sentence report phrase
A permitted NTFS attribute-flag transition can persist malformed mapping pairs by shrinking the record before moving its payload, without evidence of kernel OOB corruption or authorization bypass.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm whether malformed mapping pairs can cause kernel-side filesystem shutdown or affect data outside the triggering file.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ntfs: move attribute payload before shrinking its record [ Upstream
Commit: 7dc2c524608039d1b082a0087f7aa0751edd4ffb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7dc2c524608039d1b082a0087f7aa0751edd4ffb
Changed files:
fs/ntfs/ea.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=7dc2c524608039d1b082a0087f7aa0751edd4ffb
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99101 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99101
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: Not available
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L
The Best / paranoid CVSS score: 4.4
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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