[CVE-2026-72322][MODERATE 7.0] ipv6: mcast: Fix potential UAF in MLD delayed work [ Upstream

[CVE-2026-72322][MODERATE 7.0] ipv6: mcast: Fix potential UAF in MLD delayed work [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72322
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ipv6: mcast: Fix potential UAF in MLD delayed work [ Upstream
Commit: f12b63ef26a035c5a29b3ef56401e38199010d4a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f12b63ef26a035c5a29b3ef56401e38199010d4a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72322
Analysis date: Sat, 15 Aug 2026 07:23:11 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race between IPv6 MLD packet processing and netdevice teardown can resurrect an `inet6_dev` reference after refcount zero and schedule delayed work that later accesses freed memory, causing a kernel panic and requiring manual review due to the UAF lifetime pattern.

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

The original Linux kernel CVE announcement for CVE-2026-72322 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72322

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
======================================================================

CVE-2026-72322	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A race in IPv6 MLD handling can occur when inet6_dev teardown overlaps with incoming MLD query or report processing and delayed work scheduling. The receive path may still see the inet6_dev pointer under RCU after its refcount reached zero, and the old code could resurrect the reference with a plain refcount increment before scheduling MLD work. When the RCU deferred free later completes, the scheduled work may access freed inet6_dev memory, causing a use after free and kernel crash. For the CVSS the PR:N is used in the paranoid network adjacent interpretation because an attacker on the same L2 IPv6 segment may supply the MLD traffic while the teardown race is the hard timing condition. Impact is at least denial of service via kernel panic and in worst case may allow confidentiality or integrity impact due to UAF memory corruption. YES REQUIRES MANUAL CHECK.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE DANGER RACE UAF SKB HARDWARE IPV6 KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6	NO	NO	checked

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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:

* Remote reachable / network-triggerable: +2
  Incoming MLD query/report packets can participate in the vulnerable path. This is realistically adjacent-network/L2 IPv6 exposure, not Internet-routable remote exposure.

* Memory corruption, weak primitive: +1
  The bug is a race-dependent UAF, but the patch does not show attacker-controlled reclaim, type confusion, callback control, arbitrary write, or controlled object replacement.

* Real lifetime corruption: +1
  The issue is explicitly a refcount/RCU lifetime bug where `inet6_dev` can reach refcount 0, be scheduled for RCU free, and later be accessed by delayed work.

* Reliable kernel crash / strong DoS: +1
  The commit states that the delayed work can access freed memory and cause a kernel panic.

* Common networking core / packet-processing path: +1
  IPv6 multicast MLD receive and delayed work handling is part of a normal networking path.

Subtracted signals:

* Hard or unreliable race / special timing required: -1
  The bug requires overlap between device teardown and incoming MLD processing.

Effective paranoid score is capped at 5 by the race-UAF downgrade rule because no concrete reclaim, overwrite, type confusion, callback hijack, or refcount takeover primitive is demonstrated.

## 3. Reachability analysis

An adjacent IPv6 host on the same L2 segment may supply MLD traffic, so the packet input side is network-influenced. Reliable triggering also requires a concurrent local device teardown or namespace/device lifecycle event, which makes the race condition non-trivial.

In typical deployments, tearing down the relevant netdevice usually requires local privileges such as CAP_NET_ADMIN. In container or namespace-heavy environments, delegated network administration or unprivileged user namespaces may lower the practical barrier. The affected code is in IPv6 multicast handling, a broadly available networking subsystem, but the complete trigger requires a narrow teardown window.

Call-site confidence: high. The provided patch shows the affected reference acquisition sites and delayed work scheduling paths directly.

## 4. Severity interpretation

This is not an ordinary low-risk cleanup. It is a real RCU/refcount lifetime bug leading to UAF and kernel panic.

Realistic impact is strongest for DoS because the demonstrated consequence is a delayed-work access to freed `inet6_dev` memory. Theoretical LPE concern exists because UAF is involved, but the patch does not demonstrate attacker-controlled reclaim, overwrite, type confusion, or a usable corruption primitive. Therefore this should be treated as Actionable Moderate at minimum, with manual review, but not automatically as High-end Important.

## 5. One-sentence report phrase

A race between IPv6 MLD packet processing and netdevice teardown can resurrect an `inet6_dev` reference after refcount zero and schedule delayed work that later accesses freed memory, causing a kernel panic and requiring manual review due to the UAF lifetime pattern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a network-influenced RCU/refcount UAF in IPv6 MLD delayed work. Even though the demonstrated impact is kernel crash and the race is hard, the lifetime-corruption class and adjacent-network packet involvement make auto-close inappropriate.

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

Patch: ipv6: mcast: Fix potential UAF in MLD delayed work [ Upstream
Commit: f12b63ef26a035c5a29b3ef56401e38199010d4a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f12b63ef26a035c5a29b3ef56401e38199010d4a

Changed files:
  include/net/addrconf.h
  net/ipv6/mcast.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=f12b63ef26a035c5a29b3ef56401e38199010d4a

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

The original Linux kernel CVE announcement for CVE-2026-72322 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72322

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 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).