[CVE-2026-72434][MODERATE 7.0] netfilter: ipset: make sure gc is properly stopped [ Upstream

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

CVE: CVE-2026-72434
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: ipset: make sure gc is properly stopped [ Upstream
Commit: c940d1b96248c3081b664ede5418078bdc7c8c07
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c940d1b96248c3081b664ede5418078bdc7c8c07
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72434
Analysis date: Sun, 16 Aug 2026 04:05:30 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
ipset set destruction may fail to stop timeout GC delayed work, allowing the GC worker to be requeued after teardown and potentially access freed ipset hash data, causing local DoS and requiring manual review for UAF impact.

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

The original Linux kernel CVE announcement for CVE-2026-72434 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72434

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-2026-72434	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-362;*CWE-416;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'ipset set destruction could fail to stop the timeout GC delayed work because cancel_delayed_work_sync does not prevent the GC handler from queueing itself again. If the set is destroyed while the GC path requeues work, a later GC run may access already released ipset hash data, making this a race based use after free candidate. For the CVSS the PR:L is used in the paranoid score because triggering requires local control of ipset operations, but CAP_NET_ADMIN may be delegated to container root or a network management service rather than full host root. The issue is not directly network reachable through packet traffic and is triggered through the local netfilter ipset control plane. Impact is at least local denial of service via stall or kernel crash and in the worst defensible case may allow confidentiality or integrity impact due to use after free memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-72434 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	REMOTE SIMPLEFIX NETFILTER  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, weak/indirect corruption candidate: +1
  The GC delayed work can survive set destruction and later operate on data associated with the destroyed ipset hash object, making this a UAF candidate, but no controlled reclaim or overwrite primitive is shown.

* Real lifetime corruption: +1
  This is a delayed work lifetime bug. `cancel_delayed_work_sync()` waits for current work but does not prevent the GC callback from requeueing itself.

* Reliable kernel crash / strong DoS: +1
  The fixed bug is related to incomplete GC shutdown and previous RCU stall reports. A stale GC worker can plausibly cause stall, warning, crash, or use-after-free.

* Broad/default/common subsystem: +1
  Netfilter/ipset is a common kernel firewall subsystem, although this is control plane rather than packet data path.

* Hard or unreliable race / special timing required: -1
  Trigger depends on teardown racing with delayed work requeue.

* Requires CAP_NET_ADMIN in typical deployments: -1
  Conservative scoring uses partial penalty rather than full -2 because CAP_NET_ADMIN is often delegated to containers or network-management services and is not always equivalent to full host root.

Paranoid signals:

* Local unprivileged trigger: +1
  In configurations with unprivileged user namespaces or delegated network namespaces, an attacker may obtain CAP_NET_ADMIN inside a namespace and reach ipset control paths without full host root.

* Memory corruption, weak/indirect corruption candidate: +1
  The stale delayed work can reference freed ipset hash state.

* Real lifetime corruption: +1
  The patch changes cancellation to disabling, which directly addresses a workqueue lifetime issue.

* Weak LPE concern: +1
  The delayed work callback after object teardown is a plausible UAF review target, but the patch does not show attacker-controlled reclaim, controlled overwrite, or a demonstrated privilege-escalation primitive.

* Reliable kernel crash / strong DoS: +1
  RCU stall or kernel crash is realistic.

* Broad/default/common subsystem: +1
  Netfilter/ipset exposure is common enough to avoid treating this as obscure.

* Hard or unreliable race / special timing required: -1
  The exploitability depends on a race between destroy and GC requeue.

## 3. Reachability analysis

The bug is triggered through the local netfilter ipset control plane, not by ordinary network packets. Typical triggering requires permission to create or destroy ipsets, normally CAP_NET_ADMIN. In containerized or namespace-enabled environments, CAP_NET_ADMIN may be delegated to container root or a reduced-privilege network service, so PR:L is a defensible paranoid interpretation.

The path is not remotely reachable by packet traffic alone. Realistic exploitation requires local control over ipset objects with timeout-based GC enabled and a race with set destruction.

Call-site confidence: medium. The patch shows the lifetime-sensitive helper and the workqueue API change, but not all destroy callers or GC callback internals.

## 4. Severity interpretation

This is not an ordinary low-risk cleanup because it fixes a workqueue teardown race where GC can be requeued after destruction. Realistic demonstrated impact is local DoS through RCU stall, warning, crash, or stale work execution. Theoretical memory corruption exists as a UAF candidate, but no concrete reclaim, write primitive, type confusion, or privilege escalation path is demonstrated in the patch.

Conservative interpretation is Borderline Moderate with manual review recommended. Paranoid interpretation is Actionable Moderate because of the UAF-like delayed work lifetime issue in a common netfilter subsystem and possible namespace-delegated CAP_NET_ADMIN reachability.

## 5. One-sentence report phrase

ipset set destruction may fail to stop timeout GC delayed work, allowing the GC worker to be requeued after teardown and potentially access freed ipset hash data, causing local DoS and requiring manual review for UAF impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a race-based delayed-work lifetime bug with a plausible use-after-free after set destruction. The patch does not prove LPE, but the object lifetime pattern is risky enough that it should not be auto-closed.

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

Patch: netfilter: ipset: make sure gc is properly stopped [ Upstream
Commit: c940d1b96248c3081b664ede5418078bdc7c8c07
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c940d1b96248c3081b664ede5418078bdc7c8c07

Changed files:
  net/netfilter/ipset/ip_set_hash_gen.h

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=c940d1b96248c3081b664ede5418078bdc7c8c07

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

The original Linux kernel CVE announcement for CVE-2026-72434 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72434

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:H/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: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: 3
  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).