* [CVE-2026-97610][MODERATE REGULAR] netfs: Fix uninitialized return value in netfs_unbuffered_write()
@ 2026-09-26 20:26 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-26 20:26 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97610
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfs: Fix uninitialized return value in netfs_unbuffered_write()
Commit: 3d038eebdbd400c3bc4b66bd8aa0dff0c2bcce26
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3d038eebdbd400c3bc4b66bd8aa0dff0c2bcce26
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97610
Analysis date: Sat, 26 Sep 2026 16:26:04 -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-2026-97610 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97610
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-2026-97610 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-97610 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:L';*CWE-457;CWE-908;*CWE-200;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N';BEST CVSS score: '5';DESCR 'An uninitialized int in netfs_unbuffered_write can be returned when preparation of the first subrequest fails or when the iterator is empty. A synchronous CIFS write may therefore receive an unrelated error or an incorrect positive byte count instead of wreq error, which can cause limited application data consistency or availability impact. The returned value may also expose a small stale kernel stack value to the calling process, but the code does not provide a UAF, OOB write, or arbitrary write primitive. For the CVSS the PR:N value in the paranoid network scenario reflects that a malicious CIFS server does not need privileges on the client, although user interaction is required because a client must connect to the server and perform a write. The realistic local scenario uses PR:L because a local process must issue the affected write. No practical privilege escalation path is established, but the possible kernel stack value exposure and network influenced CIFS path justify manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) SKIP CVE-2026-97610 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE REMOTE WRITE OOB DISK SIMPLEFIX LINUS LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
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
Positive signals:
* +1 Local unprivileged trigger. A process with write access to an existing CIFS mount can issue the affected synchronous unbuffered or direct write without host-admin-equivalent privilege.
* +1 Confidentiality plausible. The uninitialized local integer can become the observable write return value, potentially exposing a small stale kernel-stack value to the calling process.
Non-awarded signals:
* Remote reachability was not awarded. A CIFS server can influence preparation failure, but the victim must first mount the share and perform a write. The return value is delivered to the local caller, not disclosed to the server.
* Integrity was not awarded. An incorrect positive byte count may confuse the calling application, but no unauthorized modification of kernel state or another principal's protected data is established.
* Reliable crash or Availability impact was not awarded. The patch establishes an incorrect return value, not a kernel crash, stall, or resource exhaustion.
* No corruption bonus was awarded. There is no UAF, OOB access, arbitrary write, refcount error, or object-lifetime violation.
* No semantic-reinterpretation bonus was awarded. The uninitialized scalar is an incorrect ordinary value rather than active control, ownership, pointer, or descriptor state.
* Broad-exposure bonus was withheld because the specific synchronous CIFS unbuffered or DIO failure path is not shown to be broadly exercised.
* No privilege-escalation or practical exploit-chain signal is established.
3. Reachability analysis
An ordinary process can reach the vulnerable code by issuing a synchronous unbuffered or direct write to a writable CIFS file. The relevant attacker is therefore a local user or service process with normal file permissions, not necessarily a host administrator.
A CIFS mount must already exist. The supplied evidence does not establish that the attacker can create that mount, but mount creation is not required for a user who already has access to a provisioned share. No capability or namespace-scoped privilege is required for the actual write operation, so namespace privilege is not relevant.
A malicious or malfunctioning CIFS server may provoke the preparation failure by preventing file reopen or credit acquisition. This is not scored as direct remote reachability because exploitation still depends on the client mounting the share and initiating the affected write, and the possible stale value is returned locally rather than over the network.
There is no race, special hardware requirement, boot option, or narrow timing condition.
4. Primitive and severity interpretation
The exact primitive is a user-observable uninitialized scalar return from a kernel write path. It is not memory corruption and does not involve stale storage, object lifetime, cleanup after free, or a repeated release or refcount mutation.
The demonstrated consequence is that a synchronous write can return an unrelated error or an incorrect byte count instead of the stored request error. A limited disclosure of one stale stack integer is technically plausible because the value may cross the syscall boundary, but the complete surrounding caller code is not supplied.
The issue is classified as CLASS_C because it produces invalid externally visible state without an independently useful kernel-corruption primitive. There is no evidence of kernel control-flow influence, protected-object modification, arbitrary read or write, or privilege escalation.
ImportantCandidate is NO because the established primitive is limited to an incorrect scalar return and possible small disclosure. AutoDowngradeAllowed is YES because no unresolved lifetime, ownership, authorization, or controlled-corruption primitive remains.
Likely operational severity is Low-like to ordinary Moderate.
5. One-sentence report phrase
An uninitialized return value in the netfs synchronous write path may expose a small stale kernel stack value or report an incorrect CIFS write result, but no memory corruption, kernel crash, or privilege escalation primitive is established.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Confirm whether every affected compiler and caller path can return the raw uninitialized integer directly to userspace, or whether upper layers normalize invalid error and byte-count values.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: netfs: Fix uninitialized return value in netfs_unbuffered_write()
Commit: 3d038eebdbd400c3bc4b66bd8aa0dff0c2bcce26
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3d038eebdbd400c3bc4b66bd8aa0dff0c2bcce26
Commit description:
If preparation of the first subrequest fails,
netfs_unbuffered_write() exits its loop before ret is initialized. The
empty-iterator check can do the same.
For synchronous writes, netfs_unbuffered_write_iter_locked() may then
return an unrelated error instead of wreq->error. This is reachable
through CIFS if cifs_prepare_write() fails to reopen the file or obtain
credits.
Initialize ret to 0 so the caller returns wreq->error if no data was
written, or the number of bytes already written otherwise.
Found with Clang's -Wconditional-uninitialized.
Fixes: a0b4c7a ("netfs: Fix unbuffered/DIO writes to dispatch subrequests in strict sequence")
Cc: [email protected]
Signed-off-by: Karl Mehltretter <[email protected]>
Signed-off-by: David Howells <[email protected]>
Link: https://patch.msgid.link/[email protected]
Acked-by: Paulo Alcantara <[email protected]>
Signed-off-by: Christian Brauner (Amutable) <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/netfs/direct_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=3d038eebdbd400c3bc4b66bd8aa0dff0c2bcce26
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97610 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97610
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:L/I:L/A:N
The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:L
The Best / paranoid CVSS score: 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: 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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