[CVE-2026-52921][LOW] netfilter: ipset: stop hash:* range iteration at end

[CVE-2026-52921][LOW] netfilter: ipset: stop hash:* range iteration at end

[AL-KERNEL]

CVE: CVE-2026-52921
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: netfilter: ipset: stop hash:* range iteration at end
Commit: be75218fadea22e59c8673db212f29c681bf45bb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=be75218fadea22e59c8673db212f29c681bf45bb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52921
Analysis date: Wed, 24 Jun 2026 04:42:12 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A netfilter ipset IPv4 range iterator could advance past the requested upper bound and cause later retries to continue from an unintended position, leading primarily to local control-plane resource exhaustion when an attacker can modify ipset state.

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

The original Linux kernel CVE announcement for CVE-2026-52921 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52921

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-52921	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:N/A:H';CWE-190;CWE-834;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'ipset hash variants for IPv4 ranges could advance a 32 bit range iterator after the final requested address was already processed. This can move retry state beyond the original range boundary and may cause later retries to continue from an unintended position. For the CVSS the PR:L is used for the paranoid score because untrusted containers or delegated network administration can sometimes provide CAP_NET_ADMIN like control without full host root privileges. The issue is not directly network reachable and is triggered through netfilter control plane updates rather than packet traffic. Impact is primarily denial of service through excessive iteration or resource consumption. No concrete UAF, OOB write, arbitrary write, or information leak primitive is indicated by the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	REMOTE OOB SIMPLEFIX NETFILTER  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Availability impact realistic: +1. The iterator can advance past the requested IPv4 range boundary and make a later retry continue from an unintended position, plausibly causing excessive iteration or resource consumption.
* Requires CAP_NET_ADMIN in typical deployments: -2. Creating or modifying ipset hash ranges is a netfilter control-plane operation and normally requires administrative network privileges.
* Netfilter subsystem exposure: +1. ipset is part of netfilter, but this is not the packet-processing fast path and is not directly reachable from network traffic.

Paranoid adjustment:

* Reduced-privilege CAP_NET_ADMIN environments: +1 relative to conservative handling. In containers, network namespaces, or delegated administration setups, CAP_NET_ADMIN may be available to an actor that is not full host root.
* No memory-corruption signal. The patch only changes iterator termination. It does not show UAF, OOB write, arbitrary write, object lifetime corruption, or information disclosure.

## 3. Reachability analysis

The bug is triggered through ipset range update operations for specific IPv4 hash set variants. In ordinary host deployments, this requires CAP_NET_ADMIN or equivalent administrative control over netfilter state. It is not triggered by incoming packets and is not remotely reachable through the data plane. Namespaces or containers may lower the practical privilege barrier if CAP_NET_ADMIN is delegated, but the attacker still needs control-plane access to ipset operations. The path is common enough to avoid a rare-subsystem penalty, but the affected condition depends on large IPv4 ranges and retry behavior.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource-exhaustion issue, not an Important-class kernel vulnerability. The realistic impact is availability degradation through unintended range traversal or retry continuation. There is no demonstrated memory corruption primitive, no confidentiality impact, no integrity impact, and no plausible privilege escalation path from the patch context.

## 5. One-sentence report phrase

A netfilter ipset IPv4 range iterator could advance past the requested upper bound and cause later retries to continue from an unintended position, leading primarily to local control-plane resource exhaustion when an attacker can modify ipset state.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for urgent triage purposes unless additional evidence appears showing memory corruption, a reliable host-wide DoS, or unprivileged reachability without delegated CAP_NET_ADMIN.

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

Patch: netfilter: ipset: stop hash:* range iteration at end
Commit: be75218fadea22e59c8673db212f29c681bf45bb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=be75218fadea22e59c8673db212f29c681bf45bb

Commit description:

The following hash set variants:

hash:ip,mark
hash:ip,port
hash:ip,port,ip
hash:ip,port,net

iterate IPv4 ranges with a 32-bit iterator.

The iterator must stop once the last address in the requested range has
been processed. Advancing it once more can move the traversal state past
the end of the request, so a later retry may continue from an unintended
position.

Handle the iterator increment explicitly at the end of the loop and stop
once the upper bound has been processed. This keeps the existing retry
behaviour intact for valid ranges while preventing traversal from
continuing past the original boundary.

Fixes: 48596a8 ("netfilter: ipset: Fix adding an IPv4 range containing more than 2^31 addresses")
Cc: stable@kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Signed-off-by: Nan Li <tonanli66@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/netfilter/ipset/ip_set_hash_ipmark.c
  net/netfilter/ipset/ip_set_hash_ipport.c
  net/netfilter/ipset/ip_set_hash_ipportip.c
  net/netfilter/ipset/ip_set_hash_ipportnet.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=be75218fadea22e59c8673db212f29c681bf45bb

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

The original Linux kernel CVE announcement for CVE-2026-52921 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52921

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:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 1
  Paranoid ActionableScore: 2

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).