[CVE-2026-45897][LOW] netfilter: nft_counter: serialize reset with spinlock [ Upstream

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

CVE: CVE-2026-45897
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: netfilter: nft_counter: serialize reset with spinlock [ Upstream
Commit: 0cdc6d5a26f2d1f7f15a43526841b679445c32e2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0cdc6d5a26f2d1f7f15a43526841b679445c32e2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45897
Analysis date: Wed, 27 May 2026 22:36:24 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
Concurrent nftables counter dump-and-reset operations can double subtract the same values, causing local counter accounting underflow without memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-45897 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45897

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-2026-45897	LOW	CHECK	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:L/A:L';CWE-362;CWE-667;CWE-682;CWE-191;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'nft_counter dump and reset operations were not serialized, so two concurrent reset requests could read the same counter values and both subtract them. This can underflow or corrupt nftables counter accounting and make firewall statistics unreliable. For the CVSS the PR:L is used in the paranoid score because delegated CAP_NET_ADMIN in containers or service accounts can expose nftables control plane operations below full host root, while normal host triggering requires network administration privileges. The issue is not network reachable and is triggered through local netfilter configuration operations rather than packet traffic. Impact is limited to counter integrity and possible low availability impact in management workflows. No supported evidence indicates information disclosure, kernel memory corruption, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1) 	MAYBE	REMOTE LOCK SIMPLEFIX NETFILTER HARDWARE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

* Integrity impact plausible: +1
  Concurrent reset can corrupt nftables counter accounting by double subtracting the same fetched values.

* Local delegated network administration trigger: +1 in paranoid scoring
  Delegated `CAP_NET_ADMIN` in containers or service accounts may expose nftables counter reset operations below full host root.

* Requires CAP_NET_ADMIN in typical deployments: -2 conservative
  nftables object/rule/set counter reset operations are normally local firewall control-plane operations requiring network administration privileges.

* No availability impact in conservative scoring: +0
  This is primarily counter/statistics underflow, not a crash, hang, memory leak, or packet-processing outage.

* No memory corruption: +0
  The issue is race-based accounting inconsistency, not UAF, OOB write, arbitrary write, or object lifetime corruption.

* No remote reachability: +0
  Packet traffic updates counters, but the vulnerable operation is local concurrent dump-and-reset through netfilter control plane.

## 3. Reachability analysis

A local actor with nftables administration rights can trigger the issue by issuing concurrent counter dump-and-reset operations. In normal host deployments this requires `CAP_NET_ADMIN`. In namespaces or containerized systems, delegated network administration may allow a less privileged tenant or service account to affect counters in its namespace.

The issue is not remotely triggerable by network packets alone. Realistic exploitation is limited to inaccurate counter values or management/statistics disruption.

## 4. Severity interpretation

This behaves like Low or ordinary Moderate. It affects accounting integrity, but does not compromise packet filtering decisions, does not corrupt kernel memory, and does not provide privilege escalation or information disclosure. The main risk is unreliable firewall statistics after concurrent reset operations.

## 5. One-sentence report phrase

Concurrent nftables counter dump-and-reset operations can double subtract the same values, causing local counter accounting underflow without memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The issue is a local `CAP_NET_ADMIN` accounting race with no memory corruption, no remote reachability, and no demonstrated security-boundary bypass.

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

Patch: netfilter: nft_counter: serialize reset with spinlock [ Upstream
Commit: 0cdc6d5a26f2d1f7f15a43526841b679445c32e2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0cdc6d5a26f2d1f7f15a43526841b679445c32e2

Changed files:
  net/netfilter/nft_counter.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=0cdc6d5a26f2d1f7f15a43526841b679445c32e2

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

The original Linux kernel CVE announcement for CVE-2026-45897 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45897

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:H/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:N/I:L/A:L
  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: 0
  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).