[CVE-2026-98124][LOW] smb/client: invalidate fscache for fallocate range operations [ Upstream

[CVE-2026-98124][LOW] smb/client: invalidate fscache for fallocate range operations [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98124
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: smb/client: invalidate fscache for fallocate range operations [ Upstream
Commit: 93c6e5a8d7c5071d586c1411596d5db5faad22b2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=93c6e5a8d7c5071d586c1411596d5db5faad22b2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98124
Analysis date: Sat, 26 Sep 2026 14:05:45 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98124 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98124

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-2026-98124	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98124 CHECK WITH IMPACT FROM ORIG NN 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:L/I:L/A:N';CWE-524;*CWE-664;*CWE-200;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'A stale data issue in the SMB client can occur because SMB3 server side range operations update file contents without invalidating the associated FS-Cache cookie. A local process can perform zero range, punch hole, insert range, or collapse range operations and later read outdated cached data instead of the current server data. This can cause an integrity failure for applications that rely on correct file contents. For the CVSS the PR:L metric is used because the attacker needs local access to the CIFS mount plus sufficient permissions to modify and read the affected file. The issue is not directly network reachable because it requires a local client process using the mounted SMB filesystem. The paranoid score also considers limited confidentiality impact because data from a range expected to be cleared or removed can remain readable from cache. The patch context does not demonstrate an SMB permission bypass, cross user disclosure, memory corruption, privilege escalation, or denial of service.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	DISK SERVERTOCLIENT LINUS MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=1
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Local unprivileged trigger. A non-administrative local user who has read and write permissions for a file on an already configured CIFS mount can invoke supported range operations and later observe stale cached content after normal page-cache eviction.
* No remote reachability bonus. The affected code runs in the local SMB client and requires a local process using the mounted filesystem.
* No UAF, OOB access, double release, refcount misuse, arbitrary write, controlled reclaim, or active-object lifetime primitive is established.
* No confidentiality bonus. The supplied reproducer reads data previously written by the same local client process. The patch does not establish cross-user data disclosure, SMB ACL bypass, or access to a protected file.
* No integrity bonus under the ActionableScore rules. The demonstrated result is incorrect stale readback, but not unauthorized modification of another principal data, filesystem metadata, or protected kernel state.
* No availability bonus. No crash, resource exhaustion, filesystem shutdown, or persistent denial of service is established.
* No paranoia-only point is awarded. Limited confidentiality impact remains a possible CVSS interpretation for stale data expected to be removed, but the supplied patch does not demonstrate an independently permissioned reader obtaining data it could not otherwise read.

3. Reachability analysis

The evaluated attacker is a local process using an existing SMB or CIFS mount with FS-Cache enabled and an active CacheFiles backend. The attacker needs sufficient file permissions to perform the relevant server-side range operation and to read the file afterward.

The reproducer uses root because it invokes `/proc/sys/vm/drop_caches`, but root is not inherently required for the vulnerable SMB client operation itself. A file owner or another user with suitable access may perform `fallocate` range operations and encounter stale data after ordinary cache eviction or equivalent normal cache lifecycle behavior.

The FS-Cache-enabled CIFS mount and backend require prior system configuration, normally by an administrator. This is an environmental prerequisite, not evidence that the attacker must have host-admin-equivalent privileges after the mount is available. No namespace-scoped full trigger chain is established.

4. Primitive and severity interpretation

The exact defect is a cache-consistency logic error. SMB3 zero range, punch hole, insert range, and collapse range operations modify server-side file contents while the corresponding local FS-Cache cookie remains valid. A later local read can therefore return data cached before the server-side modification.

This is not a UAF, stale post-free object access, ownership/COW violation, authorization bypass, or memory-corruption primitive. The stale object is cached file data rather than freed active kernel storage. The demonstrated consequence is incorrect local file readback.

A theoretical worst case is that pre-modification bytes remain observable after a caller expects the relevant range to have been cleared, removed, or shifted. However, the patch does not establish that this crosses an SMB permission boundary, exposes data to an unauthorized user, enables file modification outside existing permissions, or supports privilege escalation.

PrimitiveClass is NONE. ImportantCandidate is NO because no concrete kernel-corruption, ownership, authorization, or security-boundary primitive remains unresolved. AutoDowngradeAllowed is YES because the issue is a constrained stale-cache correctness problem with no demonstrated exploitation leverage beyond stale data returned to an authorized local reader.

Likely operational severity is ordinary Moderate or Low-like depending on whether applications rely on the affected CIFS mount for security-sensitive deletion, zeroing, or data-consistency workflows.

5. One-sentence report phrase

A local process using an FS-Cache enabled CIFS mount can receive stale file data after SMB3 server-side range operations because the client does not invalidate the corresponding FS-Cache cookie.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a stale-cache consistency defect without memory corruption, authorization bypass, cross-user disclosure, privilege escalation, or denial of service.

7. Call-site confidence

Call-site confidence: medium

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: smb/client: invalidate fscache for fallocate range operations [ Upstream
Commit: 93c6e5a8d7c5071d586c1411596d5db5faad22b2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=93c6e5a8d7c5071d586c1411596d5db5faad22b2

Changed files:
  fs/smb/client/smb2ops.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=93c6e5a8d7c5071d586c1411596d5db5faad22b2

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98124 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98124

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:L/UI:N/S:U/C:N/I:L/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
  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: 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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).