[CVE-2026-74565][MODERATE 7.0] netfilter: nf_tables: make nft_object rhltable per table [ Upstream

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

CVE: CVE-2026-74565
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: nf_tables: make nft_object rhltable per table [ Upstream
Commit: 1948e4f85b855618b5b9a27265f98d816f4cb7cb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1948e4f85b855618b5b9a27265f98d816f4cb7cb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74565
Analysis date: Sat, 15 Aug 2026 18:18:15 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A global nf_tables nft_object rhltable allowed object lookups across table and network namespace lifetime boundaries, creating a possible use-after-free when an object was destroyed in one namespace while still reachable from another lookup path.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74565 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74565

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 7.0
Manual review required: YES

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

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-74565	MODERATE	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:H/I:H/A:H';*CWE-416;CWE-362;CWE-668;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use-after-free risk exists in nf_tables object lookup because nft_object names were stored in a global rhltable shared across tables and network namespaces. An object being dismantled and immediately released in one netns could still be reached from a lookup path in another netns, creating a stale object access window. For the CVSS the PR:L is selected because reliable triggering requires local nftables netlink control or CAP_NET_ADMIN in a network namespace, but full host root may not be required when user namespaces or delegated network administration are available. The issue is not directly network reachable and is triggered through local control plane operations rather than packet traffic. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel use-after-free. For the paranoid score, choose the highest still-defensible interpretation supported by the bug class and patch context, with preference for manual-review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE OOB INIT NETFILTER UAF  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  In configurations with unprivileged user namespaces, a local user may gain CAP_NET_ADMIN inside a network namespace and exercise nf_tables control-plane operations.

* Memory corruption, weak/indirect corruption candidate: +1
  The commit explicitly describes a possible use-after-free, but the patch does not show attacker-controlled reclaim, object replacement, callback control, arbitrary write, or type confusion.

* Real lifetime corruption: +1
  A global nft_object rhltable could keep objects reachable across netns/table lifetime boundaries while nft_obj_destroy() releases them immediately.

* Reliable kernel crash / strong DoS: +1
  A stale nft_object lookup can plausibly lead to UAF dereference and kernel crash.

* Broad/default/common subsystem: +1
  nf_tables is a widely deployed kernel firewall subsystem, even though this is the control plane rather than the packet fast path.

Subtracted signals:

* Hard or unreliable race / special timing required: -1
  The problematic condition depends on object dismantling/destruction in one namespace while lookup occurs from another namespace.

* Requires CAP_NET_ADMIN in typical deployments, namespace-delegable: -1
  This is not normally reachable by a plain local process without nftables privileges, but the penalty is reduced because CAP_NET_ADMIN inside user/net namespaces can be available to non-root users on some systems.

Paranoid adjustment:

* The paranoid score is raised to 5 because this is an explicit kernel UAF in nf_tables lifetime handling and should not be auto-closed.
* The score is not raised higher because the patch does not demonstrate controlled reclaim, write-after-free, callback dispatch, type confusion, or an arbitrary read/write primitive.

## 3. Reachability analysis

The bug is triggered through nf_tables netlink control-plane operations involving nft_object lookup, creation, deletion, table teardown, and namespace interaction. It is not directly network reachable through packet traffic. In typical deployments, nftables modification requires CAP_NET_ADMIN, but user namespaces and network namespaces can reduce the practical privilege barrier when unprivileged namespace creation is enabled. The path is common enough to deserve manual review because nf_tables is broadly deployed, but exploitation likely requires careful timing around object destruction and lookup.

Call-site confidence: high. The patch shows lookup, insert, remove, table init, table destroy, commit, abort, and release paths.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because the commit explicitly identifies a possible use-after-free in a common kernel subsystem. Realistic demonstrated impact is most likely local DoS through a stale object access or crash. Theoretical privilege escalation cannot be ruled out because UAF bugs in nf_tables have historically been security-sensitive, but this patch alone does not show a strong exploitation primitive such as controlled reclaim, object confusion, or arbitrary write.

Therefore this should be treated as Actionable Moderate at minimum, with manual review required.

## 5. One-sentence report phrase

A global nf_tables nft_object rhltable allowed object lookups across table and network namespace lifetime boundaries, creating a possible use-after-free when an object was destroyed in one namespace while still reachable from another lookup path.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: explicit kernel use-after-free candidate in nf_tables object lifetime handling, namespace-dependent reachability, and possible local privilege escalation concern despite no demonstrated strong primitive in the patch.

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

Patch: netfilter: nf_tables: make nft_object rhltable per table [ Upstream
Commit: 1948e4f85b855618b5b9a27265f98d816f4cb7cb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1948e4f85b855618b5b9a27265f98d816f4cb7cb

Changed files:
  include/net/netfilter/nf_tables.h
  net/netfilter/nf_tables_api.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=1948e4f85b855618b5b9a27265f98d816f4cb7cb

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

The original Linux kernel CVE announcement for CVE-2026-74565 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74565

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:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 4
  Paranoid ActionableScore: 5

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 7.0

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).