[CVE-2026-98119][LOW] netfs: break unbuffered write when netfs_alloc_subrequest() fails [ Upstream

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

CVE: CVE-2026-98119
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: netfs: break unbuffered write when netfs_alloc_subrequest() fails [ Upstream
Commit: cf6f93b8b06acf57de62dacbe71a3b99c68656a7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cf6f93b8b06acf57de62dacbe71a3b99c68656a7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98119
Analysis date: Sat, 26 Sep 2026 15:55:26 -0400
ActionableScore: 2
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-2026-98119 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98119

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-2026-98119	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98119 CHECK WITH IMPACT FROM ORIG NN NONE	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:N/A:H';**CWE-476;CWE-252;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A NULL-pointer dereference in the netfs unbuffered write path occurs because netfs_prepare_write() continued to initialize a subrequest after netfs_alloc_subrequest() returned NULL. A local process with write access to a file on an affected netfs backed filesystem can reach this path, although reliable triggering normally depends on an allocation failure caused by severe memory pressure or fault injection. For the CVSS the PR:L value is selected because an attacker needs local user or process context and permission to issue writes, but does not necessarily need administrative control when allocation failure occurs naturally. The issue is not directly network reachable merely because a remote filesystem such as 9p is used, since the vulnerable operation is initiated through a local write request. Impact is denial of service through a kernel Oops or panic. The analyzed code provides no UAF, OOB access, information disclosure, or controlled memory corruption primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)  SKIP CVE-2026-98119 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	REMOTE WRITE KASAN OOB NULLPTR DISK NOMEMCHK LINUS SYZBOT  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

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

2. Signal breakdown

* +1 Local unprivileged trigger. A local process with permission to write an affected netfs-backed file can reach the vulnerable unbuffered-write path without host-admin privilege.
* +1 Reliable kernel crash / strong DoS. A failed subrequest allocation is followed by a write through `subreq == NULL`, producing the demonstrated KASAN NULL-pointer fault near address `0xa8`.
* +0 Weak corruption concern. The operation is a fixed NULL-pointer dereference, not a useful attacker-selected pointer or target.
* No extra Availability point was awarded because the Oops or panic is the same consequence already counted as strong DoS.
* No UAF, stale object, OOB access, repeated release, refcount corruption, controlled reclaim, arbitrary write, disclosure, or authorization bypass is established.
* No confidentiality or integrity signal was awarded.
* No remote-reachability signal was awarded. A network-backed filesystem does not make this local VFS write path remotely triggerable.
* No filesystem-integrity signal was awarded because the patch establishes a crash during allocation failure, not cross-file corruption, metadata corruption, or an ownership violation.
* No allocation-failure penalty was applied. Fault injection demonstrates the failure path, but ordinary allocation failure remains possible and no rare configuration is required by the vulnerable code itself.

3. Reachability analysis

An ordinary local process can enter the path by issuing an unbuffered write to a file it is permitted to modify on an affected netfs-backed filesystem, with 9p shown in the trace. Mounting or exposing that filesystem normally requires prior system configuration, but the attacker does not need host-administrator privilege for the subsequent file write.

The demonstrated reproducer forces `netfs_alloc_subrequest()` to fail using failslab, which itself is a privileged testing mechanism. However, fault injection is not intrinsic to the defect. The same NULL return can occur under genuine allocation failure, although an unprivileged attacker may not be able to force it reliably. No namespace capability is required or relevant to the write operation. There is no race, special hardware dependency, or direct network trigger.

4. Primitive and severity interpretation

The exact primitive is a write through a NULL `struct netfs_io_subrequest` pointer after `netfs_alloc_subrequest()` fails. The resulting access is at a small fixed offset from address zero and is expected to fault rather than provide attacker-directed kernel memory corruption.

This is CLASS_C invalid-state and crash behavior. It is not an active-object UAF, fixed stale-storage UAF, repeated lifetime mutation, or structured post-free use. The demonstrated consequence is a kernel Oops or panic. Stronger consequences such as arbitrary kernel write, information disclosure, privilege escalation, filesystem corruption, or cross-ownership modification are not supported.

ImportantCandidate is NO because no independently useful corruption or boundary primitive survives after excluding the crash. AutoDowngradeAllowed is YES because the issue is a constrained allocation-failure NULL dereference with DoS as its established impact.

5. One-sentence report phrase

A local writer can trigger a kernel NULL-pointer dereference if netfs subrequest allocation fails during an unbuffered write, resulting in denial of service without an established memory-corruption or privilege-escalation primitive.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a fixed NULL-pointer crash caused by missing allocation-failure handling, with no UAF, controlled corruption, disclosure, authorization bypass, or unresolved lifetime primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: netfs: break unbuffered write when netfs_alloc_subrequest() fails [ Upstream
Commit: cf6f93b8b06acf57de62dacbe71a3b99c68656a7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cf6f93b8b06acf57de62dacbe71a3b99c68656a7

Changed files:
  fs/netfs/write_issue.c
  fs/netfs/direct_write.c
  fs/9p/vfs_file.c
  fs/read_write.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=cf6f93b8b06acf57de62dacbe71a3b99c68656a7

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

The original Linux kernel CVE announcement for CVE-2026-98119 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98119

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:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 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: 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).