[CVE-2026-64189][MODERATE 7.0] netfilter: ipset: fix race between dump and ip_set_list resize

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

CVE: CVE-2026-64189
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: netfilter: ipset: fix race between dump and ip_set_list resize
Commit: ff86ea9b7fdf70564e60436fbee68c96bc459943
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ff86ea9b7fdf70564e60436fbee68c96bc459943
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64189
Analysis date: Mon, 20 Jul 2026 12:51:59 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in netfilter ipset dump cleanup can read a freed `ip_set_list` array during concurrent resize, causing a race-based use-after-free and kernel crash, with possible but unproven privilege-escalation relevance in delegated `CAP_NET_ADMIN` environments.

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

The original Linux kernel CVE announcement for CVE-2026-64189 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64189

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-2026-64189	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-667;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 condition in netfilter ipset can occur when the dump release path reads inst ip_set_list while a concurrent ip_set_create operation resizes and frees the old array. The dump path uses ip_set_ref_netlink without an RCU read side critical section, so synchronize_net does not protect it and the old array can be freed while it is still indexed. This leads to a slab use-after-free in ip_set_dump_do and can crash the kernel through a general protection fault or panic. For the CVSS the PR:L is used for the paranoid score because a local user with delegated network administration rights, container root, or user namespace based CAP_NET_ADMIN may be able to drive the required ipset netlink operations without being full host root. The issue is not directly reachable from remote packet traffic and is triggered through local netfilter control plane operations. Impact is at least local denial of service. In worst case it may allow confidentiality or integrity impact due to a race based use-after-free and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE READ OOB LOCK DANGER NETFILTER RACE UAF KPANIC 	NO	NO	guess

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

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

## 2. Signal breakdown

Triggered signals:

* Memory corruption, weak/indirect corruption candidate: +1
  The bug is a race-based UAF of the old `ip_set_list` array. The stale array entry is read and then interpreted as a `struct ip_set *`.

* Real lifetime corruption: +1
  This is an RCU lifetime bug. The dump path reads an RCU-published array without `rcu_read_lock()`, so `synchronize_net()` does not protect it.

* Reliable kernel crash / strong DoS: +1
  The report shows KASAN slab-use-after-free, general protection fault, and kernel panic in `ip_set_dump_do()`.

* Weak LPE concern: +1
  The stale value is not just read and discarded. It is used as an object pointer and then dereferenced through `set->variant->uref`, which is callback-adjacent object interpretation. No controlled reclaim is shown, so this is weak concern only.

* Broad/default/common subsystem exposure: +1
  Netfilter/ipset is a commonly deployed kernel networking control-plane subsystem, although this is not the packet fast path.

Subtracted signals:

* Hard or unreliable race / special timing required: -1 for conservative score
  Triggering requires overlap between netlink dump release and `ip_set_create()` resize. The KASAN report suggests practical reproducibility, so the paranoid score does not subtract this.

* Requires CAP_NET_ADMIN in typical deployments: -1
  ipset management normally requires `CAP_NET_ADMIN`. I do not apply the full -2 penalty because CAP_NET_ADMIN is often delegated into containers or network namespaces and may be held by a reduced-privilege actor rather than full host root.

Not counted:

* Remote reachable: +0
  This is not triggered by ordinary remote packets.

* Strong LPE plausibility: +0
  No attacker-controlled reclaim, arbitrary write, refcount takeover, or reliable type confusion primitive is shown.

* Confidentiality/Integrity impact as demonstrated: +0 conservative
  The demonstrated impact is crash. C/I remain only a paranoid review concern due to UAF object-pointer use.

Call-site confidence: high. The patch shows the affected call sites and the immediate dereference after `ip_set_ref_netlink()`.

## 3. Reachability analysis

The bug is triggered locally through netfilter/ipset netlink control-plane operations. A typical host user needs `CAP_NET_ADMIN` to create or resize ipsets and to drive the dump path. In containerized or namespaced environments, this may be reachable by container root or by a service account with delegated network administration rights, so treating it as full host-root-only would understate practical exposure.

The path is not remotely reachable through packet processing. Realistic exploitation requires the ability to issue ipset netlink operations and win a race between dump cleanup and array resize. The provided KASAN trace from a task named `exploit` indicates the race is not merely theoretical.

## 4. Severity interpretation

This is stronger than an ordinary Moderate DoS because it is a real race-based UAF in netfilter control-plane code, with a demonstrated kernel crash and stale object-pointer use. It is not a clear Important-class issue by itself because the patch does not show controlled reclaim, write-after-free, arbitrary write, or a proven privilege-escalation primitive.

The realistic demonstrated impact is local kernel crash. The theoretical concern is that stale array contents may be interpreted as an `ip_set` object and dereferenced through callback-related fields, so manual review is warranted for possible exploitability beyond DoS.

## 5. One-sentence report phrase

A race in netfilter ipset dump cleanup can read a freed `ip_set_list` array during concurrent resize, causing a race-based use-after-free and kernel crash, with possible but unproven privilege-escalation relevance in delegated `CAP_NET_ADMIN` environments.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a demonstrated race-based UAF in a netfilter control-plane path, with stale object-pointer dereference and callback-adjacent use. It should not be auto-closed as a simple DoS without manual review.

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

Patch: netfilter: ipset: fix race between dump and ip_set_list resize
Commit: ff86ea9b7fdf70564e60436fbee68c96bc459943
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ff86ea9b7fdf70564e60436fbee68c96bc459943

Commit description:

The release path of ip_set_dump_do() and ip_set_dump_done() read
inst->ip_set_list via ip_set_ref_netlink(), a plain rcu_dereference_raw()
of the array pointer. These run from netlink_recvmsg() without the nfnl
mutex and without an RCU read-side critical section.

A concurrent ip_set_create() can grow the array: it publishes the new
array, calls synchronize_net() and then kvfree()s the old one. Since the
dump paths read the array outside any RCU reader, synchronize_net() does
not wait for them and the old array can be freed while they still index
into it, causing a use-after-free.

The dumped set itself stays pinned via set->ref_netlink, so only the
array load needs protecting. Take rcu_read_lock() around it, matching
ip_set_get_byname() and __ip_set_put_byindex().

  BUG: KASAN: slab-use-after-free in ip_set_dump_do (net/netfilter/ipset/ip_set_core.c:1697)
  Read of size 8 at addr ffff88800b5c4018 by task exploit/150
  Call Trace:
   ...
   kasan_report (mm/kasan/report.c:595)
   ip_set_dump_do (net/netfilter/ipset/ip_set_core.c:1697)
   netlink_dump (net/netlink/af_netlink.c:2325)
   netlink_recvmsg (net/netlink/af_netlink.c:1976)
   sock_recvmsg (net/socket.c:1159)
   __sys_recvfrom (net/socket.c:2315)
   ...
  Oops: general protection fault, probably for non-canonical address ... KASAN NOPTI
  KASAN: maybe wild-memory-access in range [0x02d6...d0-0x02d6...d7]
  RIP: 0010:ip_set_dump_do (net/netfilter/ipset/ip_set_core.c:1698)
  Kernel panic - not syncing: Fatal exception

Fixes: 8a02bdd ("netfilter: ipset: Fix calling ip_set() macro at dumping")
Cc: stable@vger.kernel.org
Reported-by: Weiming Shi <bestswngs@gmail.com>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Xiang Mei <xmei5@asu.edu>
Acked-by: Jozsef Kadlecsik <kadlec@netfilter.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/netfilter/ipset/ip_set_core.c
  mm/kasan/report.c
  net/netlink/af_netlink.c
  net/socket.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=ff86ea9b7fdf70564e60436fbee68c96bc459943

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

The original Linux kernel CVE announcement for CVE-2026-64189 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64189

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: 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: 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).