[CVE-2024-39503][MODERATE 7.0] netfilter: ipset: Fix race between namespace cleanup and gc in the list:set type [ Upstream

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

CVE: CVE-2024-39503
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: netfilter: ipset: Fix race between namespace cleanup and gc in the list:set type [ Upstream
Commit: c0761d1f1ce1d5b85b5e82bbb714df12de1aa8c3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c0761d1f1ce1d5b85b5e82bbb714df12de1aa8c3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2024-39503
Analysis date: Wed, 20 May 2026 23:35:20 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race between ipset namespace cleanup and list:set garbage collection can leave delayed GC code accessing freed set data, causing a kernel use-after-free with at least local DoS impact and possible higher impact in namespace or container deployments.

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

The original Linux kernel CVE announcement for CVE-2024-39503 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2024-39503

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-2024-39503	MODERATE	CHECK	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-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in netfilter ipset list:set can let namespace cleanup destroy a set while its garbage collector is still pending through RCU cleanup, causing a use-after-free when the delayed GC later accesses freed set data. For the CVSS the PR:L is used in the paranoid score because CAP_NET_ADMIN may be available to a reduced privilege container root or a user namespace based attacker in some deployments, even though host wide ipset administration is normally privileged. The issue is local control-plane reachable and is not directly network reachable through packet traffic. Impact is at least denial of service via kernel crash, and because this is a real lifetime UAF in a kernel netfilter object, worst case confidentiality and integrity impact should remain open for manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	REMOTE LOCK INIT NETFILTER RACE UAF TEST  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	YES	YES	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Paranoid score signals:

* Generic memory corruption, strong corruption primitive: +2
  The commit explicitly describes a use-after-free where list:set GC can access an already destroyed set.

* Real lifetime corruption: +1
  This is an RCU and GC lifetime ordering bug. Namespace cleanup can free ipset objects while delayed GC still holds a path to them.

* Weak LPE concern: +1
  UAF in kernel netfilter objects can theoretically be exploitable beyond DoS, but the patch does not show a controlled reclaim or arbitrary write primitive.

* Reliable kernel crash / strong DoS: +1
  A delayed GC dereferencing destroyed set data is a credible kernel crash path.

* Availability impact realistic: +1
  The failure can affect the host kernel, not only the network namespace being destroyed.

* Cross-boundary isolation concern: +1
  The bug is tied to network namespace teardown and ipset state. In containerized environments, namespace lifecycle and CAP_NET_ADMIN delegation may make this more relevant than a pure host-admin bug.

* Broad/default/common subsystem exposure: +1
  Netfilter is widely deployed. ipset/list:set is not always used, but it is a standard netfilter component and should not be treated as rare-only.

Subtractions:

* Hard or unreliable race / special timing required: -1
  The issue depends on the ordering between namespace cleanup, RCU cleanup, and list:set GC.

Conservative lower score:

* UAF memory corruption: +2
* Real lifetime corruption: +1
* Reliable crash / DoS: +1
* Availability realistic: +1
* Requires CAP_NET_ADMIN in typical host deployments: -2
* Race / timing requirement: -1
* Broad netfilter exposure: +1

Conservative total: 4.

## 3. Reachability analysis

The bug is local control-plane reachable, not directly network-triggerable through packet traffic. A typical host attacker needs privileges to create and manage ipset state and to tear down the related network namespace, usually CAP_NET_ADMIN or comparable administrative control.

Namespaces and containers matter. If CAP_NET_ADMIN is delegated inside a container or user namespace and ipset operations are available, the practical privilege requirement may be lower than full host root. That is why the conservative score treats this as a privileged local DoS/UAF, while the paranoid score treats it as a container or namespace-relevant UAF requiring manual review.

The path is not necessarily default-active because list:set and its GC must be used. However, it is not an exotic hardware-only path and belongs to a common kernel networking subsystem.

## 4. Severity interpretation

This is more than an ordinary Moderate because the patch fixes a real UAF, not only a warning or resource leak. The realistic demonstrated impact is local DoS via kernel crash. The theoretical higher impact is local privilege escalation through UAF exploitation, but the patch does not demonstrate attacker-controlled reclaim, arbitrary write, or a reliable object-confusion primitive.

Conservative handling is Borderline / manual review recommended. Paranoid handling is Strong Important candidate because it combines RCU lifetime corruption, netfilter objects, namespace teardown, and possible delegated CAP_NET_ADMIN reachability.

## 5. One-sentence report phrase

A race between ipset namespace cleanup and list:set garbage collection can leave delayed GC code accessing freed set data, causing a kernel use-after-free with at least local DoS impact and possible higher impact in namespace or container deployments.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should be reviewed manually because it is a race-based UAF in a netfilter namespace cleanup path, and delegated CAP_NET_ADMIN or containerized deployments may reduce the practical privilege barrier.

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

Patch: netfilter: ipset: Fix race between namespace cleanup and gc in the list:set type [ Upstream
Commit: c0761d1f1ce1d5b85b5e82bbb714df12de1aa8c3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c0761d1f1ce1d5b85b5e82bbb714df12de1aa8c3

Changed files:
  net/netfilter/ipset/ip_set_core.c
  net/netfilter/ipset/ip_set_list_set.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=c0761d1f1ce1d5b85b5e82bbb714df12de1aa8c3

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

The original Linux kernel CVE announcement for CVE-2024-39503 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2024-39503

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: 4
  Paranoid ActionableScore: 7

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: YES
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).