[CVE-2026-64079][MODERATE 7.0] netfilter: x_tables: allocate hook ops while under mutex [ Upstream

[CVE-2026-64079][MODERATE 7.0] netfilter: x_tables: allocate hook ops while under mutex [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64079
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: x_tables: allocate hook ops while under mutex [ Upstream
Commit: 2f92c5f923979f37ab1d5445381e4b8378a196cc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2f92c5f923979f37ab1d5445381e4b8378a196cc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64079
Analysis date: Sun, 19 Jul 2026 14:25:59 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in x_tables table registration can expose a table with uninitialized hook ops during concurrent network namespace teardown, causing a NULL dereference crash, and the surrounding RCU lifetime handling makes this an Actionable Moderate issue requiring manual review.

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

The original Linux kernel CVE announcement for CVE-2026-64079 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64079

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-2026-64079	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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-476;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'x_tables table registration has a race where a table can become visible in the per netns table list before its hook ops pointer is initialized. A concurrent pernet exit path can find that table and pass a NULL ops pointer to nf_unregister_net_hooks, causing a NULL pointer dereference and kernel crash. The same registration and error unwind area also contains an RCU lifetime concern because nf_register_net_hooks may publish a hook before failing, so a packet path could still observe hook state while teardown proceeds. For the CVSS the PR:L is used for the paranoid score because reliable triggering requires local code or a local process able to create and tear down network namespaces or otherwise exercise xtables registration, but this may be available to unprivileged users on systems with user namespaces or delegated container networking. The issue is not directly network reachable and is triggered through the netfilter control plane rather than packet traffic. Impact is at least local denial of service, with a higher manual review score because the patch context indicates a possible RCU or use after free lifetime hazard.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	LOCK NULLPTR INIT NOMEMCHK NETFILTER LOG HARDWARE IPV6 PACKET  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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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 signals:

* Local unprivileged trigger: +1
  Possible on systems where unprivileged user namespaces allow a local user to create a network namespace and obtain CAP_NET_ADMIN inside it, then exercise iptables or arptables registration paths.

* Reliable kernel crash / strong DoS: +1
  The commit provides a concrete general protection fault in nf_unregister_net_hooks caused by passing table->ops == NULL.

* Broad/default/common subsystem exposure: +1
  x_tables, ip_tables, ip6_tables, and arp_tables are common netfilter compatibility paths.

* Hard or unreliable race / special timing required: -1
  Triggering requires overlap between table registration and pernet exit / network namespace teardown.

* Cross-boundary isolation impact: +1
  If reachable from an unprivileged user namespace, a namespace-local operation can crash the host kernel, which is a practical container or namespace isolation concern.

Paranoid additional signals:

* Memory corruption, weak/indirect corruption candidate: +1
  The primary demonstrated bug is NULL dereference, but the same patch area handles partially published hooks and wrong lifetime ordering.

* Real lifetime corruption / RCU lifetime issue: +1
  The added synchronize_rcu() after nf_register_net_hooks() failure indicates a possible RCU publication and teardown lifetime hazard, even though no controlled UAF primitive is demonstrated.

## 3. Reachability analysis

This is not remotely network-triggerable through packet traffic. It is a netfilter control-plane race during xtables table registration and network namespace teardown.

In traditional host configurations, triggering usually requires CAP_NET_ADMIN or equivalent privilege to manipulate iptables, ip6tables, or arptables state. However, on systems with unprivileged user namespaces enabled, a local unprivileged user may be able to create a user namespace and network namespace, gain CAP_NET_ADMIN inside that namespace, and exercise the vulnerable path. That makes PR:L a defensible paranoid interpretation.

The race is timing-dependent and requires concurrent registration and namespace cleanup, so exploitability is not trivial. The demonstrated impact is a kernel crash. The RCU synchronization added by the patch is enough to justify manual review, but not enough to claim a proven privilege escalation primitive.

Call-site confidence: high, because the patch and commit message show the registration path, list publication, pre_exit path, and concrete crash stack.

## 4. Severity interpretation

This behaves more seriously than an ordinary Moderate because it combines a common netfilter subsystem, namespace reachability, a confirmed host kernel crash, and a possible RCU lifetime concern.

Realistic impact is local DoS. Theoretical memory corruption concern exists only in the error-unwind / RCU publication area and is not supported by a demonstrated reclaim, overwrite, callback control, or type confusion primitive. Therefore this should not be treated as confirmed Important/LPE, but it should not be auto-closed as a low-risk crash either.

## 5. One-sentence report phrase

A race in x_tables table registration can expose a table with uninitialized hook ops during concurrent network namespace teardown, causing a NULL dereference crash, and the surrounding RCU lifetime handling makes this an Actionable Moderate issue requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: confirmed race-triggered kernel crash in common netfilter code, possible unprivileged namespace reachability, and an RCU lifetime cleanup change that could indicate more than a pure NULL dereference.

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

Patch: netfilter: x_tables: allocate hook ops while under mutex [ Upstream
Commit: 2f92c5f923979f37ab1d5445381e4b8378a196cc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2f92c5f923979f37ab1d5445381e4b8378a196cc

Changed files:
  net/netfilter/core.c
  include/linux/netfilter/x_tables.h
  net/ipv4/netfilter/arp_tables.c
  net/ipv4/netfilter/ip_tables.c
  net/ipv6/netfilter/ip6_tables.c
  net/netfilter/x_tables.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=2f92c5f923979f37ab1d5445381e4b8378a196cc

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

The original Linux kernel CVE announcement for CVE-2026-64079 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64079

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: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).