[CVE-2026-72321][LOW] ipv4: igmp: Fix potential memory leaks in igmp_mod_timer() and igmp_stop_timer() [ Upstream

[CVE-2026-72321][LOW] ipv4: igmp: Fix potential memory leaks in igmp_mod_timer() and igmp_stop_timer() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72321
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ipv4: igmp: Fix potential memory leaks in igmp_mod_timer() and igmp_stop_timer() [ Upstream
Commit: f60ec3058a85447008b88b762c859d336163acb3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f60ec3058a85447008b88b762c859d336163acb3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72321
Analysis date: Sun, 16 Aug 2026 04:28:41 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
IPv4 IGMP timer handling can leak multicast group objects during a race between timer deletion and group removal, allowing a local user to cause limited resource exhaustion under repeated timing dependent attempts.

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

The original Linux kernel CVE announcement for CVE-2026-72321 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72321

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.

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

CVE-2026-72321	LOW	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;CWE-362;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'IPv4 IGMP timer handling can leak ip_mc_list objects when igmp_mod_timer() or igmp_stop_timer() deletes a timer and directly decrements the multicast entry reference count while a concurrent group removal has already reduced the count to 1. The bug is a race in an RCU reader path and the observable primitive is a memory leak rather than a use after free or overwrite. For the CVSS the PR:L is used because reliable triggering requires a local user or process to create and drop multicast memberships or otherwise drive the target host state, even though IGMP traffic is adjacent network traffic. The issue is not Internet reachable in normal routing and is mainly relevant on local L2 networks where IGMP is used. Impact is denial of service through possible resource exhaustion after repeated successful races, with no supported confidentiality or integrity impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	REMOTE SIMPLEFIX LEAK NETWORK  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2

## 1. ActionableScore

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

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local unprivileged process can typically create and drop IPv4 multicast memberships through normal socket APIs, which can drive the relevant IGMP group state.

* Real lifetime or refcount bug: +1
  The bug is caused by using `refcount_dec()` instead of `ip_ma_put()` when the final reference may be dropped. This is a real object lifetime management issue, but the demonstrated result is a leak, not UAF.

Not triggered:

* Remote reachable: +0
  IGMP is local L2 traffic and the reliable trigger also depends on local host multicast group state and a concurrent removal path.

* Generic memory corruption: +0
  The patch describes leaked `ip_mc_list` objects, not UAF, double free, overwrite, type confusion, or attacker-controlled reuse.

* Strong DoS: +0
  Resource exhaustion is possible only after repeated successful race conditions. A single trigger is not shown to reliably crash the host.

Subtracted or limited:

* Hard or unreliable race: effectively limits severity
  The leak requires a timing window between IGMP timer handling and concurrent multicast group removal.

## 3. Reachability analysis

The most realistic trigger is a local process that joins and leaves IPv4 multicast groups while IGMP query or report handling runs on the same host. A remote LAN peer may influence IGMP traffic, but cannot reliably trigger the full condition alone without suitable local multicast membership churn. This is not Internet reachable in normal routing. Network namespaces may make the local trigger easier in containerized environments if untrusted users can create sockets and manipulate multicast memberships, but this still remains a local or local-network-adjacent resource leak scenario rather than a direct remote memory corruption issue.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like kernel issue. The bug is a race and a refcount lifetime mistake, but the concrete primitive is memory leakage of `ip_mc_list` objects. There is no supported confidentiality or integrity impact, no demonstrated UAF reuse, and no plausible privilege escalation path from the supplied patch context. The realistic impact is limited availability degradation through repeated resource leakage under timing-sensitive conditions.

## 5. One-sentence report phrase

IPv4 IGMP timer handling can leak multicast group objects during a race between timer deletion and group removal, allowing a local user to cause limited resource exhaustion under repeated timing dependent attempts.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a resource leak without demonstrated memory corruption, privilege escalation, information disclosure, or reliable single-shot kernel crash.

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

Patch: ipv4: igmp: Fix potential memory leaks in igmp_mod_timer() and igmp_stop_timer() [ Upstream
Commit: f60ec3058a85447008b88b762c859d336163acb3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f60ec3058a85447008b88b762c859d336163acb3

Changed files:
  net/ipv4/igmp.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=f60ec3058a85447008b88b762c859d336163acb3

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

The original Linux kernel CVE announcement for CVE-2026-72321 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72321

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: unknown
  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).