[CVE-2026-98117][MODERATE REGULAR] cachefiles: Fix potential UAF/KASAN warning [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-98117
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: cachefiles: Fix potential UAF/KASAN warning [ Upstream
Commit: 68d459e6e609c31f96a203dd6eec60c634f155e1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=68d459e6e609c31f96a203dd6eec60c634f155e1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98117
Analysis date: Fri, 25 Sep 2026 11:21:46 -0400
ActionableScore: 2
ActionableScore lower bound: 0
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-2026-98117 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98117

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-98117	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98117 CHECK WITH IMPACT FROM ORIG NN 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:L/I:N/A:H';CWE-125;*CWE-200;*CWE-457;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'The cachefiles coherency tracepoint can read eight bytes from cachefiles_xattr data even when the variable length auxiliary buffer contains fewer than eight bytes or no data. This creates an out of bounds read that may consume uninitialized or stale slab contents and can produce a KASAN warning. On systems configured with panic_on_warn the warning may result in a kernel crash and denial of service. A limited confidentiality impact is also plausible if stale kernel bytes are copied into a trace buffer that an attacker can access, but no write primitive or direct privilege escalation path is demonstrated. For the CVSS the PR:L is used because a local process may trigger cache activity on an already configured cachefiles backed filesystem, while configuring cachefiles and enabling the tracepoint normally require administrative access and are treated as environmental prerequisites. The issue is not directly network reachable, although access to a cache backed network filesystem may indirectly initiate the affected path. Impact is a possible local denial of service and limited information exposure. Manual review is required because the affected operation is a kernel heap read and the commit explicitly identifies a potential UAF condition.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)  SKIP CVE-2026-98117 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DISK UAF HARDWARE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=2
ActionableScoreLower=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Conservative signals:

* +0 Limited kernel OOB read. The trace argument reads eight bytes from variable-length data that may contain fewer than eight bytes, but the supplied code establishes no write primitive or attacker-visible disclosure.
* +0 KASAN warning. A warning alone is not a reliable kernel crash under the scoring rules.
* +0 Potential UAF wording. The visible call sites invoke the tracepoint before `kfree(buf)`, so a temporal use-after-free is not established.
* +0 Unaligned access. The two-byte alignment is insufficient for the old `__be64` access, but no fatal alignment exception is demonstrated.

Paranoid-only signals:

* +1 Confidentiality plausible. Up to eight bytes, including uninitialized or stale slab contents, may be copied into the trace record. This is a concrete output sink, although attacker access to the trace buffer is unresolved.
* +1 Strong DoS plausible. The invalid or unaligned read can produce KASAN or architecture-specific faults, and a fatal-warning configuration can convert this into a kernel panic.

Not awarded:

* Controlled reclaim, arbitrary write, type confusion, callback influence, and privilege escalation are not demonstrated.
* Real UAF points were not awarded because the visible buffer remains allocated during the trace call.
* Remote reachability was not awarded. Network-filesystem activity may initiate cache operations, but direct remote control of the vulnerable trace operation is not established.
* Local-unprivileged reachability was not awarded because the complete cachefiles and tracing privilege chain is unresolved.
* No second Availability point was awarded because no consequence distinct from the possible fault or panic exists.
* No configuration penalty was applied. Cachefiles and an enabled tracepoint are prerequisites, but the supplied evidence does not fully establish who configured them or who can subsequently trigger the affected operation.

3. Reachability analysis

The vulnerable operation requires an active cachefiles-backed workload and execution of the coherency tracepoint. Enabling cachefiles and kernel tracing normally involves privileged setup, but that does not prove that the process initiating the later cache operation must itself be host administrator.

An ordinary process with access to an already configured cached filesystem may be able to induce relevant cache activity. The supplied context does not establish that this is sufficient for every affected path, so `HostAdminRequired` remains `UNKNOWN` rather than being assumed either `YES` or `NO`.

No namespace capability check or complete namespace-scoped trigger chain is shown. `NamespaceScopedPrivilege` is therefore `UNKNOWN`. No special hardware, race, or narrow timing window is required. Direct network triggering is not established.

4. Primitive and severity interpretation

The exact primitive is a bounded kernel heap OOB read of up to eight bytes from the variable-length `cachefiles_xattr::data` area, combined with a potentially unaligned 64-bit load. The read occurs while `buf` is still live. It is therefore not a demonstrated temporal UAF, despite the commit message describing a potential UAF.

The immediate consequences are an invalid read, possible KASAN or alignment warning, and possible capture of uninitialized or stale slab bytes in a trace record. The trace record is a plausible disclosure sink, but access by a below-host-admin attacker is not established. No mutation of kernel memory, repeated release, lifetime transition, controlled replacement, or active structured stale-object use exists.

This is `CLASS_C` because the demonstrated behavior is an invalid read and warning or crash condition without an independently useful corruption primitive. `ImportantCandidate=NO` because no strong Class B or Class A mechanism exists. `AutoDowngradeAllowed=YES` because the remaining uncertainty concerns limited disclosure and conditional DoS, not unresolved write-capable corruption or a security-boundary bypass.

Likely operational severity is Low to ordinary Moderate, depending on tracing exposure and whether warnings are fatal.

5. One-sentence report phrase

A cachefiles tracepoint may read up to eight bytes beyond short auxiliary data, potentially recording stale slab bytes or causing a KASAN or alignment fault, but no temporal UAF, write primitive, or privilege escalation path is established.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether affected trace events can be enabled or read by a below-host-admin actor and whether supported production architectures can turn the unaligned or out-of-bounds access into a fatal fault.

7. Call-site confidence

Call-site confidence: high

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

Patch: cachefiles: Fix potential UAF/KASAN warning [ Upstream
Commit: 68d459e6e609c31f96a203dd6eec60c634f155e1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=68d459e6e609c31f96a203dd6eec60c634f155e1

Changed files:
  fs/cachefiles/xattr.c
  include/trace/events/cachefiles.h

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=68d459e6e609c31f96a203dd6eec60c634f155e1

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

The original Linux kernel CVE announcement for CVE-2026-98117 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98117

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:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H
  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: 0
  Paranoid ActionableScore: 2

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).