* [CVE-2026-99108][MODERATE 7.0] ntfs: fix FITRIM range alignment
@ 2026-10-30 14:36 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-30 14:36 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99108
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ntfs: fix FITRIM range alignment
Commit: 5e87da8ba8d3d647d89c754912e45c1f1a3bfc2e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5e87da8ba8d3d647d89c754912e45c1f1a3bfc2e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99108
Analysis date: Fri, 30 Oct 2026 10:36:14 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
A privileged FITRIM operation can misalign an NTFS discard range and persistently zero adjacent allocated file clusters.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99108 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99108
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 7.0
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-2026-99108 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99108 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H';CWE-682;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:L';BEST CVSS score: '6';DESCR 'ntfs_trim_fs can calculate a discard range beyond the end of a free extent because it aligns the start address up but aligns the original extent length down. This can discard allocated clusters following the free extent and cause persistent file data corruption. The demonstrated result was seven allocated clusters being zeroed after FITRIM under a 32 KiB discard granularity. For the CVSS the PR:H value reflects that issuing FITRIM normally requires CAP_SYS_ADMIN or equivalent storage administration authority. Base impact is C:N I:H A:L. The paranoid impact is C:N I:H A:H because repeated trims may corrupt enough allocated data to make files applications or the filesystem unavailable. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 6 and the production ActionableScore returned 3 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 LOW to MODERATE_KPANIC because the manual review requirement was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. final reconciliation stage MODERATE to MODERATE_KPANIC because 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 INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.6 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. 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_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) MAYBE DISK SIMPLEFIX LEAK HARDWARE LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; no floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +1 constrained destructive write: incorrect endpoint arithmetic sends a bounded discard beyond a free extent into adjacent allocated clusters; the payload is effectively discard/zeroing, not an arbitrary kernel write.
* +1 integrity impact: the reproducer confirmed seven allocated clusters were zeroed and remained corrupted across remount.
* +1 important filesystem/storage path: FITRIM acts directly on filesystem-backed allocated storage.
* +1 practical effect chain: malformed alignment calculation directly reaches `blkdev_issue_discard()` and demonstrated persistent file-data damage.
* -2 host-administrator-equivalent privilege: supplied evidence identifies FITRIM as normally requiring `CAP_SYS_ADMIN` or equivalent storage-management authority.
* Paranoid-only +1 strong availability concern: repeated trims can plausibly corrupt enough allocated data to make files, applications, or the filesystem unavailable.
* Not awarded: arbitrary payload/target, kernel-memory corruption, UAF, ownership/COW bypass, cross-user authorization bypass, confidentiality impact, or unprivileged trigger.
* The same storage corruption was not separately counted as both a crash and availability impact.
3. Reachability analysis
The trigger is a FITRIM operation on a mounted NTFS filesystem with discard granularity larger than and misaligned to the cluster layout. The supplied evidence supports effective host storage-administrator privilege, generally `CAP_SYS_ADMIN`; numeric UID 0 is not inherently required when that capability is delegated. No user-namespace-scoped complete trigger is shown. The reproduced setup uses `scsi_debug`, but the arithmetic defect is not limited to that test device; it requires discard support and a suitable free-extent alignment, not rare physical hardware or a race.
4. Primitive and severity reading
The primitive is a confirmed, constrained block discard into active allocated filesystem storage. It is CLASS_B because persistent structured storage corruption is real, while arbitrary target selection, kernel-memory overwrite, protected cross-authority victim access, and privilege escalation are not shown. The demonstrated effect is allocated-file data loss; broader filesystem unavailability is plausible but not demonstrated. Host-admin-equivalent authority materially limits security-boundary significance, so this is not an Important candidate and may be operationally downgraded after review.
5. One-sentence report phrase
A privileged FITRIM operation can misalign an NTFS discard range and persistently zero adjacent allocated file clusters.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm product FITRIM privilege enforcement and whether affected deployments expose discard-capable NTFS volumes with vulnerable alignment combinations.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ntfs: fix FITRIM range alignment
Commit: 5e87da8ba8d3d647d89c754912e45c1f1a3bfc2e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5e87da8ba8d3d647d89c754912e45c1f1a3bfc2e
Commit description:
ntfs_trim_fs() aligns the start of a free extent up to the device discard
granularity, but derives the discard length by aligning the original extent
length down. When the free extent start is not discard-aligned, adding that
length to the aligned start can extend the discard past the free extent and
into allocated clusters.
For example, with 4 KiB clusters and 32 KiB discard granularity, the free
extent [4 KiB, 36 KiB) becomes the discard range [32 KiB, 64 KiB), so
28 KiB beyond the free extent may be discarded.
Align the absolute end of the free extent down and derive the length from
the two aligned endpoints. Skip extents that contain no full discard unit.
Reproduced with a 4 KiB-cluster NTFS filesystem on scsi_debug configured
for 32 KiB discard granularity and read-zero-after-trim. Before this
change, FITRIM zeroed seven allocated 4 KiB clusters following an unaligned
32 KiB hole. With this change, the same data remains intact across FITRIM
and remount.
Fixes: 11ccc91 ("ntfs: update runlist handling and cluster allocator")
Cc: [email protected]
Assisted-by: OpenAI Codex:GPT-5.6 Sol Max
Signed-off-by: Jacopo Labardi <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/ntfs/bitmap.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=5e87da8ba8d3d647d89c754912e45c1f1a3bfc2e
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99108 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99108
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:L/PR:H/UI:N/S:U/C:N/I:H/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H
The Best / paranoid CVSS score: 6
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: 2
Paranoid ActionableScore: 3
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: YES
Published priority for this report (same as in Subject): MODERATE 7.0
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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