[CVE-2026-68338][MODERATE 7.0] net/packet: avoid fanout hook re-registration after unregister [ Upstream

[CVE-2026-68338][MODERATE 7.0] net/packet: avoid fanout hook re-registration after unregister [ Upstream

[AL-KERNEL]

CVE: CVE-2026-68338
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/packet: avoid fanout hook re-registration after unregister [ Upstream
Commit: 80ec024d53a05c60ad1d08968dcf745f10c1665c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=80ec024d53a05c60ad1d08968dcf745f10c1665c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68338
Analysis date: Mon, 10 Aug 2026 13:53:58 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race between packet_set_ring() and NETDEV_UNREGISTER can re-register an AF_PACKET fanout hook after the bound device was unregistered, leaving a stale net_device association that can cause local DoS and may represent a weak UAF candidate in namespace or delegated-capability environments.

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

The original Linux kernel CVE announcement for CVE-2026-68338 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68338

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.

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

CVE-2026-68338	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-362;*CWE-416;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 between packet_set_ring and NETDEV_UNREGISTER can allow an AF_PACKET fanout hook to be re registered after the bound network device has already been unregistered. The vulnerable window appears when packet_set_ring drops bind_lock while reconfiguring the ring, while the netdevice notifier invalidates the socket binding by setting ifindex to -1 and clearing the per socket device pointer. A one member fanout group may still retain a shared hook device pointer, so re registering based only on the stale was_running state can leave a hook associated with a dead device. For the CVSS the PR:L value is used for the paranoid score because an attacker may only need delegated CAP_NET_RAW and CAP_NET_ADMIN inside a namespace or container like environment, rather than full host administrator privileges. The issue is not directly network reachable and requires local control over packet socket and network device lifecycle operations. Impact is at least local denial of service. In the worst still defensible interpretation, the stale hook on an unregistered device is a use-after-free candidate with possible confidentiality and integrity impact, so manual review is recommended.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	REMOTE INIT RACE HARDWARE PACKET  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative scoring:

* Weak or indirect corruption candidate: +1. The stale fanout hook can retain a device pointer after NETDEV_UNREGISTER, but the patch does not show attacker-controlled reclaim, overwrite, callback control, or object replacement.
* Real lifetime corruption: +1. The bug is a race where a hook may be re-registered after the referenced net_device binding was invalidated.
* Reliable kernel crash / strong DoS: +1. Re-adding a hook to a dead device can plausibly lead to kernel crash or networking teardown failure.
* Broad/default/common subsystem exposure: +1. AF_PACKET and netdevice unregister paths are common Linux networking facilities.
* Common networking / packet-processing path: +1. The bug affects packet socket fanout hook registration, which interacts with packet delivery.
* Hard or unreliable race / special timing required: -1. Triggering requires racing packet_set_ring() with NETDEV_UNREGISTER while bind_lock is dropped.
* Requires CAP_NET_RAW and CAP_NET_ADMIN or equivalent in typical deployments: -2. Reliable triggering normally requires privileged packet socket and network device lifecycle control.

Paranoid scoring differences:

* Local lower-privilege trigger: +1. In namespace or container-like environments, delegated CAP_NET_RAW and CAP_NET_ADMIN may make this reachable by a less trusted local actor rather than full host root.
* The Race-UAF downgrade rule applies. This is treated as weak memory corruption plus lifetime corruption, not as a strong UAF primitive, because no controlled reclaim, write-after-free, type confusion, callback dispatch control, or refcount takeover is shown.
* Paranoid score is capped at 5 for a race-dependent stale pointer / UAF candidate without a demonstrated exploitation primitive.

## 3. Reachability analysis

The issue is local, not directly network reachable. A realistic trigger requires creating or controlling an AF_PACKET socket with fanout/ring configuration and racing that operation with unregistering the bound network device.

In typical host deployments this requires CAP_NET_RAW for packet sockets and CAP_NET_ADMIN for network device management, so the conservative interpretation treats it as privileged. In environments with user namespaces, containers, or delegated network administration, those capabilities may be available to a less trusted local user or service account, which supports the paranoid PR:L-like interpretation.

The affected subsystem is common, but the exact trigger is timing-sensitive and requires a specific AF_PACKET fanout plus NETDEV_UNREGISTER interaction.

## 4. Severity interpretation

This is above ordinary Moderate because it is a real networking lifetime race involving a stale net_device hook after unregister. It should not be auto-closed as a simple DoS-only correctness bug.

However, it is not a strong Important candidate on the available evidence. The patch supports a plausible stale pointer / UAF candidate and local DoS, but it does not show attacker-controlled reclaim, arbitrary write, type confusion, function pointer control, or a demonstrated privilege escalation path.

Overall this behaves like an Actionable Moderate at minimum, with manual review required to decide whether the stale fanout hook can be turned into stronger memory corruption.

## 5. One-sentence report phrase

A race between packet_set_ring() and NETDEV_UNREGISTER can re-register an AF_PACKET fanout hook after the bound device was unregistered, leaving a stale net_device association that can cause local DoS and may represent a weak UAF candidate in namespace or delegated-capability environments.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: this is a race in a common networking lifetime path with a stale device hook after unregister. Even though no controlled reclaim or LPE primitive is demonstrated, the stale net_device reference makes it unsuitable for automatic closure.

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

Patch: net/packet: avoid fanout hook re-registration after unregister [ Upstream
Commit: 80ec024d53a05c60ad1d08968dcf745f10c1665c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=80ec024d53a05c60ad1d08968dcf745f10c1665c

Changed files:
  net/packet/af_packet.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=80ec024d53a05c60ad1d08968dcf745f10c1665c

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

The original Linux kernel CVE announcement for CVE-2026-68338 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68338

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: 3
  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: NO
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).