[CVE-2026-72463][IMPORTANT] xfrm: Fix dev use-after-free in xfrm async resumption [ Upstream

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

CVE: CVE-2026-72463
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: xfrm: Fix dev use-after-free in xfrm async resumption [ Upstream
Commit: 63a30015199912bd5055bead8001b1ae68a67cdb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=63a30015199912bd5055bead8001b1ae68a67cdb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72463
Analysis date: Sat, 15 Aug 2026 06:34:02 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
XFRM async resumption can incorrectly drop a reference on a tunnel skb dev changed by xfrm_rcv_cb, causing net_device refcount corruption and possible UAF reachable through configured IPsec or VTI traffic, with realistic DoS and worst-case privilege-escalation concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72463 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72463

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: IMPORTANT
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-2026-72463	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'XFRM async resumption can hit a use-after-free of a net_device because skb dev may be changed by xfrm_rcv_cb to a tunnel device such as VTI without taking a matching device reference. The async path previously kept the original receive device reference until transport_finish, but later dev_put could be applied to the modified tunnel device instead, causing refcount imbalance, possible tunnel device UAF, and a leaked reference on the original device. A remote peer may contribute by sending traffic to an IPsec or VTI XFRM endpoint while async processing and device teardown or reconfiguration overlap. For the CVSS the PR:N value is used because the attacker does not need local privileges on the victim when the vulnerable XFRM endpoint is reachable, although valid tunnel or IPsec traffic and a specific configuration may be needed. Impact is at least denial of service via network device lifetime corruption and kernel instability. For the paranoid score, C:H/I:H/A:H is defensible because the patch context explicitly describes a use-after-free in a network device object, but exploitation is high complexity due to the race and configuration requirements.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8)  SKIP CVE-2026-72463 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 1c428b03840094410c5fb6a5db30640486bbbfcb YES  NO NO unknown 	MAYBE	REMOTE LOCK RACE LEAK UAF NETWORK SKB HARDWARE IPV6 KPANIC 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  XFRM input is packet-processing code. A remote IPsec/VTI peer can plausibly influence this path by sending traffic to a configured XFRM/VTI endpoint.

* Memory corruption, weak/indirect corruption candidate: +1
  The commit explicitly describes a dev use-after-free, but the patch does not demonstrate controlled reclaim, arbitrary write, callback control, or reliable object replacement.

* Real lifetime corruption: +1
  The bug is a net_device lifetime/refcount mismatch. skb->dev may be changed to a tunnel device without a matching reference, and later dev_put can hit the wrong object.

* Weak LPE concern: +1
  This is not only a NULL dereference. It is refcount abuse and UAF of a net_device object in the network stack, so limited privilege-escalation concern is defensible, though not proven.

* Reliable kernel crash / strong DoS: +1
  The reported symptom includes unregister_netdevice waiting and negative usage count, indicating serious device lifetime corruption and kernel instability.

* Common networking packet-processing path: +1
  XFRM/IPsec is a core networking subsystem. It is configuration-dependent, but it should not be treated as an obscure debug-only path.

Negative signal:

* Hard or unreliable race / special timing required: -1
  Practical exploitation likely requires async processing plus overlap with tunnel device teardown or reconfiguration.

Conservative total: 6

Paranoid additional signals:

* Confidentiality impact plausible: +1
  Because this is a real UAF in a kernel network object, a cautious manual-review score can include possible read-side impact, although no direct info leak is shown.

* Integrity impact plausible: +1
  A UAF/refcount lifetime bug in net_device handling can plausibly corrupt trusted kernel state in worst-case analysis, although no write primitive is demonstrated.

Paranoid total: 8

## 3. Reachability analysis

A remote peer may trigger the vulnerable path by sending traffic to a system configured as an XFRM/IPsec/VTI endpoint. For CVSS-style PR reasoning, PR:N is defensible when the endpoint is network reachable because the attacker does not need a local account on the victim. In practice, exploitation depends on a specific deployment with XFRM/VTI, async processing, and timing overlap with device teardown or reconfiguration.

Local namespaces mainly affect setup, not the remote packet trigger. Creating or reconfiguring VTI/XFRM devices usually requires CAP_NET_ADMIN, but the packet-side trigger can come from outside once the endpoint exists. The path is not default-enabled on all systems, but XFRM/IPsec is common enough in networking deployments that this should not be auto-closed as niche.

Call-site confidence: high. The provided patch shows the affected xfrm_input flow and the IPv4/IPv6 transport_finish call sites.

## 4. Severity interpretation

This is above ordinary Moderate. The realistic impact is strong DoS from network-device lifetime corruption and potential UAF. The strongest proven facts are refcount imbalance, wrong dev_put target, RCU lifetime race, and possible net_device UAF.

Theoretical privilege escalation is not demonstrated, because there is no shown attacker-controlled reclaim, arbitrary write, callback hijack, or type confusion. However, because the affected object is a net_device in packet-processing code and the commit explicitly calls out UAF, manual review is required. The issue fits an Actionable Moderate at minimum and a Strong Important candidate under paranoid triage.

## 5. One-sentence report phrase

XFRM async resumption can incorrectly drop a reference on a tunnel skb dev changed by xfrm_rcv_cb, causing net_device refcount corruption and possible UAF reachable through configured IPsec or VTI traffic, with realistic DoS and worst-case privilege-escalation concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

YES REQUIRES MANUAL CHECK. This is a network-reachable lifetime corruption bug with explicit UAF wording in the commit context, so it should not be auto-closed even though reliable exploitation appears race-dependent and configuration-dependent.

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UPSTREAM PATCH SUMMARY
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Patch: xfrm: Fix dev use-after-free in xfrm async resumption [ Upstream
Commit: 63a30015199912bd5055bead8001b1ae68a67cdb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=63a30015199912bd5055bead8001b1ae68a67cdb

Changed files:
  net/ipv4/xfrm4_input.c
  net/ipv6/xfrm6_input.c
  net/xfrm/xfrm_input.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=63a30015199912bd5055bead8001b1ae68a67cdb

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

The original Linux kernel CVE announcement for CVE-2026-72463 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72463

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:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 6
  Paranoid ActionableScore: 8

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).