[CVE-2026-64150][MODERATE REGULAR] netfilter: nft_inner: release local_lock before re-enabling softirqs [ Upstream

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

CVE: CVE-2026-64150
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: nft_inner: release local_lock before re-enabling softirqs [ Upstream
Commit: df19b6af171695a1352314597c9a4311d48d5171
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=df19b6af171695a1352314597c9a4311d48d5171
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64150
Analysis date: Sun, 19 Jul 2026 16:29:15 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Borderline only if nft_inner traffic path is exposed
Manual review required: NO

Summary:
A locking order bug in `nft_inner` can re-enable softirqs before releasing a per-CPU local lock in an error path, potentially causing packet-path stalls or DoS on systems with affected nftables inner-header rules.

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

The original Linux kernel CVE announcement for CVE-2026-64150 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64150

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 REGULAR
Manual review required: NO

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-2026-64150	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-667;CWE-703;CWE-662;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.9';DESCR 'nft_inner has a locking order bug in an error path where softirqs can be re enabled before the per CPU local lock is released. This can violate nested BH locking assumptions and may lead to lockdep warnings, stalls, or denial of service when traffic reaches the affected nft_inner path. For the CVSS the PR:N is used because an external packet sender does not need local privileges once a vulnerable nftables configuration is already deployed. The issue is network reachable only in systems that use nft_inner rules and where packet processing can hit the cookie mismatch error path. Impact is availability only in the base assessment, with no clear evidence of UAF, OOB access, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Borderline only if nft_inner traffic path is exposed (with actual score 3)  SKIP CVE-2026-64150 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: ba36fada9ab4 YES  NO NO unknown 	MAYBE	REMOTE LOCK SIMPLEFIX NETFILTER ERRORPATH HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Borderline only if nft_inner traffic path is exposed**

## 2. Signal breakdown

* Remote reachable / network-triggerable: +2
  Applies only after a vulnerable nftables configuration using `nft_inner` is already deployed. A packet sender may reach the affected packet-processing path without local privileges.

* Common networking / packet-processing path: +1
  This is netfilter packet-path code, but the affected `nft_inner` path is configuration-dependent rather than universally active.

* Hard or special triggering condition: -1
  The issue is in an error path where the per-CPU tunnel context cookie does not match the current skb. This is not a generic packet receive crash path.

* No memory corruption bonus: +0
  The patch only fixes ordering between `local_unlock_nested_bh()` and `local_bh_enable()`. It does not show UAF, OOB access, double free, stale callback, arbitrary write, or type confusion.

* Reliable DoS: +0 conservative, +1 paranoid
  Conservative assessment treats this as a locking-order correctness bug. Paranoid assessment allows possible stall or lockup on sensitive configurations such as PREEMPT_RT or lockdep-sensitive paths.

## 3. Reachability analysis

An external packet sender may trigger the affected code only if the system already has nftables rules that exercise `nft_inner` and the packet reaches the cookie-mismatch restore path. Creating or modifying those rules normally requires `CAP_NET_ADMIN`, but that is an environmental precondition rather than a privilege required from a remote packet sender.

Namespaces and containers matter mainly for configuration control. If an untrusted container or service has delegated `CAP_NET_ADMIN` over a relevant netns, local triggering becomes more practical. In normal host deployments, rule setup is administrator-controlled.

The affected subsystem is netfilter, but `nft_inner` is not a default always-on path. Realistic exploitation looks like availability degradation in a specifically configured firewall path, not privilege escalation.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like networking DoS correctness issue, not an Important-class vulnerability. The theoretical concern is that enabling softirqs before releasing a per-CPU local lock can violate nested BH locking assumptions and cause warnings, stalls, or deadlock-like behavior. The realistic evidence from the patch supports availability impact only.

There is no demonstrated memory corruption primitive, no confidentiality impact, no integrity impact, and no plausible LPE path from the provided diff.

## 5. One-sentence report phrase

A locking order bug in `nft_inner` can re-enable softirqs before releasing a per-CPU local lock in an error path, potentially causing packet-path stalls or DoS on systems with affected nftables inner-header rules.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can usually be auto-handled as a low-risk Moderate because the patch shows a lock-ordering DoS candidate only, with no UAF, OOB access, arbitrary write, information disclosure, or privilege-escalation primitive. Manual review is only useful for products that heavily use `nft_inner`, PREEMPT_RT, or expose firewall rule control to less-trusted tenants.

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

Patch: netfilter: nft_inner: release local_lock before re-enabling softirqs [ Upstream
Commit: df19b6af171695a1352314597c9a4311d48d5171
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=df19b6af171695a1352314597c9a4311d48d5171

Changed files:
  net/netfilter/nft_inner.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=df19b6af171695a1352314597c9a4311d48d5171

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

The original Linux kernel CVE announcement for CVE-2026-64150 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64150

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.9

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: 2
  Paranoid ActionableScore: 3

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 REGULAR

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).