* [CVE-2026-99242][MODERATE REGULAR] ntfs: fix race between fallocate and mmap reads [ Upstream
@ 2026-11-03 2:58 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-11-03 2:58 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99242
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ntfs: fix race between fallocate and mmap reads [ Upstream
Commit: 7dd1c2fec6ebdd1a88a02cb58ff515a258eeb327
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7dd1c2fec6ebdd1a88a02cb58ff515a258eeb327
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99242
Analysis date: Mon, 02 Nov 2026 22:58:42 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
A local user can race NTFS fallocate against mmap faults to read newly allocated clusters before zeroing, exposing stale disk contents.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99242 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99242
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-2026-99242 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99242 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N';CWE-362;*CWE-200;CWE-367;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N';BEST CVSS score: '6.3';DESCR 'A race in NTFS fallocate can expose newly allocated clusters through concurrent mmap page faults after the clusters are added to the runlist but before ntfs_dio_zero_range clears their previous contents. This provides a concrete local information disclosure primitive because stale disk data can be returned to userspace and may also create file data integrity problems if stale pages remain in the page cache. For the CVSS the PR:L value is selected because exploitation requires a local user or process able to invoke fallocate and mmap on the same writable NTFS file. AC:H reflects the need to win the timing window between cluster mapping and zeroing. There is no supported UAF OOB access or kernel memory corruption primitive and the issue is not directly network reachable. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 6.3 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. 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 V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.1 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE READ DISK SIMPLEFIX RACE LEAK V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=CONFIRMED
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 additional technically supported effect.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +1 Local unprivileged trigger: a process with ordinary write and mmap access to its own NTFS file can invoke both operations; host administration is not required.
* +1 Practical exploit chain: fallocate publishes newly allocated clusters in the runlist, and a concurrent mmap fault can read them before zeroing.
* +1 Confidentiality impact: old disk contents are concretely returned to userspace.
* +1 Cross-ownership/isolation concern: allocation zeroing is the boundary preventing a new file allocation from exposing prior storage contents.
* +1 Important filesystem/storage path: the defect affects allocation, page-cache faulting, and zeroing consistency.
* -1 Hard timing requirement: exploitation must place a page fault between runlist publication and `ntfs_dio_zero_range()`.
Not awarded: kernel-memory corruption, UAF, OOB access, arbitrary write, LPE, remote reachability, or a second availability point. Integrity concerns are described, but no unauthorized modification of another principal’s protected object is established, so no separate integrity point is scored. B5-R, B3-PENDING, and B4-PENDING do not apply.
3. Reachability analysis
The grounded actor is a local user or process able to fallocate and mmap the same writable file on a mounted NTFS filesystem. No UID 0, capability, namespace privilege, prior privileged policy setup, or special hardware is shown as necessary. The race window is real but timing-sensitive and can be attempted using concurrent operations.
4. Primitive and severity reading
The primitive is a concrete stale-storage disclosure caused by missing invalidate-lock serialization, not kernel memory corruption. The patch makes runlist publication, zeroing, and mmap page faults mutually exclusive. Protected old disk contents may be exposed, but targeting particular prior data, persistent cross-file modification, or privilege escalation is not shown.
This is CLASS_B because it is a real security-relevant disclosure primitive with constrained targeting and timing. It warrants mandatory review, but the supplied evidence does not establish an Important-class exploit primitive. Auto-downgrade remains permissible after review.
5. One-sentence report phrase
A local user can race NTFS fallocate against mmap faults to read newly allocated clusters before zeroing, exposing stale disk contents.
6. Manual review advice
MANUAL CHECK REQUIRED
Confirm practical race reliability, stale-page persistence, and whether prior contents can be targeted or sampled broadly.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ntfs: fix race between fallocate and mmap reads [ Upstream
Commit: 7dd1c2fec6ebdd1a88a02cb58ff515a258eeb327
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7dd1c2fec6ebdd1a88a02cb58ff515a258eeb327
Changed files:
fs/ntfs/file.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=7dd1c2fec6ebdd1a88a02cb58ff515a258eeb327
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99242 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99242
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:H/I:L/A:N
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
The Best / paranoid CVSS score: 6.3
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: 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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