[CVE-2026-97998][MODERATE REGULAR] netfilter: nfnetlink_log: cope with concurrent instance destruction [ Upstream

[CVE-2026-97998][MODERATE REGULAR] netfilter: nfnetlink_log: cope with concurrent instance destruction [ Upstream

[AL-KERNEL]

CVE: CVE-2026-97998
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: nfnetlink_log: cope with concurrent instance destruction [ Upstream
Commit: 0234d7ca0317be0a623300e1693cd794bbfdf8af
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0234d7ca0317be0a623300e1693cd794bbfdf8af
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97998
Analysis date: Fri, 25 Sep 2026 13:50:16 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A local race in nfnetlink_log can remove the same logging instance from its hash list twice during concurrent socket-close destruction and UNBIND processing, causing a kernel general protection fault and denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-97998 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97998

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-2026-97998	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97998 CHECK WITH IMPACT FROM ORIG NN LOW	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:L/A:H';CWE-362;CWE-667;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A race in nfnetlink_log can occur when an instance is being destroyed after a netlink socket close event while another socket using the same portid submits an UNBIND request. The instance can be removed from the internal hash list twice, causing corrupted list state and a general protection fault in nfulnl_recv_config. For the CVSS the PR:L is used because configuring nfnetlink_log typically requires CAP_NET_ADMIN, which can be available to a container root or delegated service account without full host administration privileges. The issue is not directly network reachable because it is triggered through local netlink control plane operations. The confirmed impact is local denial of service through a kernel crash. The repeated list removal creates a limited potential for memory corruption impact and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	REMOTE LOCK INIT SIMPLEFIX NETFILTER SKB PACKET  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	NO	NO	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

## 1. ActionableScore

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

No floor or cap was applied.

## 2. Signal breakdown

* +1 Reliable kernel crash or strong DoS. The supplied commit documents a general protection fault in `nfulnl_recv_config()` after a second `hlist_del_rcu()` operation on an already unhashed instance.

No additional Availability point was awarded because the observed Oops and kernel DoS are the same consequence.

Important non-awarded signals:

* Real UAF not established. The commit explicitly states that instances are refcounted and memory release occurs only on the refcount transition from 1 to 0. The vulnerable behavior is repeated hash-list removal, not dereferencing an object after its lifetime has ended.
* Concrete repeated release or refcount mutation not established. The second operation is `hlist_del_rcu()`, not a second `put`, `kref_put`, `free`, or refcount decrement on a potentially freed object.
* Controlled reclaim, attacker-controlled replacement, arbitrary write, callback control, and structured stale-object reuse are not demonstrated.
* Confidentiality and integrity points were not awarded. The double-unlink produces invalid list state and an Oops, but the supplied evidence does not establish disclosure, directed corruption, or unauthorized modification of protected state.
* Remote reachability was not awarded. The vulnerable path is reached through local nfnetlink control-plane operations.
* No hard-race penalty was applied. The commit requires timing, but also says uncooperative userspace can force the relevant pending-destruction and UNBIND state. The supplied material does not establish that the race is materially rare or externally uncontrollable.
* No host-admin or niche-subsystem penalty was applied. The exact capability check and whether the entire sequence works from an attacker-controlled network namespace are not visible in the supplied context.

## 3. Reachability analysis

The triggering actor is a local process able to configure or unbind an `nfnetlink_log` instance and manipulate netlink socket lifetime. The sequence requires one queue destruction initiated by a netlink close event and another socket using the same portid to submit an UNBIND request.

Netfilter netlink configuration commonly involves `CAP_NET_ADMIN`, but the supplied patch does not show the exact capability check or its target user namespace. Therefore, host-admin-equivalent access is not positively established, and below-host-admin reachability for the complete operation is also not positively established.

`HostAdminRequired=UNKNOWN` and `NamespaceScopedPrivilege=UNKNOWN` are appropriate. A network namespace or potentially delegated `CAP_NET_ADMIN` cannot establish complete namespace-scoped reachability without confirming that instance creation, destruction, portid reuse, and UNBIND all work under the same attacker-controlled namespace.

No hardware, firmware, boot option, or prior host provisioning prerequisite is shown. The race appears reproducible through local socket and queue lifecycle activity, but the exact reliability is not established.

## 4. Primitive and severity interpretation

The exact primitive is a concurrent double unlink of an `nfulnl_instance` from an RCU hash list. The first destruction path executes `hlist_del_rcu()` and marks `copy_mode` as disabled. A concurrent or delayed UNBIND path can previously execute `hlist_del_rcu()` again before observing that the instance is already pending destruction.

This is not an active structured-object UAF. The instance remains refcounted, and the patch description explicitly distinguishes list unlinking from final memory release. The demonstrated failure is a poisoned or invalid list-pointer operation that triggers a general protection fault.

The issue is therefore `CLASS_C`, not `CLASS_A` or `CLASS_B`. The demonstrated consequence is local kernel crash or DoS. A theoretical stronger consequence from generic list corruption is not enough to establish controlled memory corruption, object replacement, arbitrary write, confidentiality impact, integrity impact, or privilege escalation.

`ImportantCandidate=NO` because no unresolved active-object lifetime primitive or attacker-useful corruption mechanism is demonstrated. `AutoDowngradeAllowed=YES` because the available evidence supports constrained crash behavior rather than a meaningful unresolved exploitation primitive.

Likely operational severity is ordinary Moderate or Low-like local DoS, depending on the product-specific accessibility of nfnetlink_log configuration.

## 5. One-sentence report phrase

A local race in nfnetlink_log can remove the same logging instance from its hash list twice during concurrent socket-close destruction and UNBIND processing, causing a kernel general protection fault and denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm the exact `CAP_NET_ADMIN` capability namespace used by nfnetlink configuration and whether an untrusted container or delegated service account can complete the full create close portid-reuse and UNBIND sequence.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: netfilter: nfnetlink_log: cope with concurrent instance destruction [ Upstream
Commit: 0234d7ca0317be0a623300e1693cd794bbfdf8af
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0234d7ca0317be0a623300e1693cd794bbfdf8af

Changed files:
  net/netfilter/nfnetlink_log.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=0234d7ca0317be0a623300e1693cd794bbfdf8af

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

The original Linux kernel CVE announcement for CVE-2026-97998 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97998

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:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 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).