[CVE-2026-64002][MODERATE 7.0] ipv4: free net->ipv4.sysctl_local_reserved_ports after unregister_net_sysctl_table() [ Upstream

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

CVE: CVE-2026-64002
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ipv4: free net->ipv4.sysctl_local_reserved_ports after unregister_net_sysctl_table() [ Upstream
Commit: ecf45080a4d3f4526cacb8b14060fe3b49a6913b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ecf45080a4d3f4526cacb8b14060fe3b49a6913b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64002
Analysis date: Sun, 19 Jul 2026 19:07:42 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in IPv4 network namespace teardown can leave `/proc/sys/net/ipv4/ip_local_reserved_ports` reachable after its backing bitmap is freed, creating a local UAF window that can plausibly cause a kernel crash and may warrant review for write-after-free impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64002 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64002

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
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CVE-2026-64002	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-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';DESCR 'A race in ipv4 network namespace teardown can expose a use after free because net ipv4 sysctl_local_reserved_ports was freed while /proc/sys/net/ipv4/ip_local_reserved_ports could still be reachable through the registered sysctl table. A local process racing sysctl access against net namespace destruction may read or write through a stale pointer to the freed bitmap. For the CVSS the PR:L is selected because a local process is needed, and unprivileged users may gain effective CAP_NET_ADMIN inside user and network namespaces on systems where this is enabled. The issue is not network reachable. Impact is at least local denial of service via kernel crash, and in the paranoid case may include confidentiality or integrity impact due to UAF based memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE SIMPLEFIX NETWORK LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local process can potentially race access to `/proc/sys/net/ipv4/ip_local_reserved_ports` against network namespace teardown. In systems with unprivileged user and network namespaces, this may be reachable without host root.

* Memory corruption, weak primitive: +1
  This is a race-dependent UAF candidate. The freed object is `net->ipv4.sysctl_local_reserved_ports`, while the sysctl table may still expose a path that can access it.

* Real lifetime corruption: +1
  The fix changes object lifetime ordering by moving `kfree()` after `unregister_net_sysctl_table()`. This directly indicates a stale access window.

* Reliable kernel crash / strong DoS concern: +1
  A sysctl access through a freed pointer can plausibly crash the kernel, although the patch does not show a concrete KASAN trace or proven reliable reproducer.

* Broad/default/common subsystem exposure: +1
  IPv4 sysctls and network namespaces are common kernel facilities.

* Hard or unreliable race / special timing required: -1
  Exploitation requires racing namespace teardown against sysctl access.

Paranoid-only elevation:

* Weak LPE concern / writable stale object concern: +1
  The sysctl path is not just passive bookkeeping. If a write-side sysctl operation can reach the freed bitmap, this becomes a possible write-after-free style corruption candidate. This is not enough to claim strong LPE, but enough to avoid auto-close.

## 3. Reachability analysis

The bug is local, not network reachable. The attacker needs local code execution and the ability to interact with network namespaces and the IPv4 sysctl entry during namespace teardown. On systems where unprivileged user namespaces and network namespaces are enabled, an unprivileged user may be able to create the relevant namespace context and trigger teardown. On hardened systems where namespace creation is restricted, the required privileges may be higher. The affected path is common kernel networking control-plane code, but the race window is narrow and teardown-dependent.

Call-site confidence: medium. The patch shows the lifetime ordering issue clearly, but the exact sysctl handler access mode and reliability of write-after-free triggering are not fully shown in the provided diff.

## 4. Severity interpretation

This is stronger than an ordinary Moderate cleanup because it fixes a real lifetime ordering bug where a proc sysctl entry can outlive its backing data. Realistic impact is most likely local DoS through a UAF crash. Theoretical impact may include limited memory corruption if a writable sysctl operation reaches the freed bitmap, but the patch does not demonstrate attacker-controlled reclaim, type confusion, arbitrary write, or a reliable privilege escalation primitive. Therefore this should be treated as Actionable Moderate at minimum, with manual review needed before downgrading.

## 5. One-sentence report phrase

A race in IPv4 network namespace teardown can leave `/proc/sys/net/ipv4/ip_local_reserved_ports` reachable after its backing bitmap is freed, creating a local UAF window that can plausibly cause a kernel crash and may warrant review for write-after-free impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is a race-based UAF in a common networking sysctl lifetime path, with possible local namespace reachability and potential writable stale-object access. It should not be auto-closed without checking the sysctl handler behavior and whether write-side access can corrupt reclaimed memory.

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

Patch: ipv4: free net->ipv4.sysctl_local_reserved_ports after unregister_net_sysctl_table() [ Upstream
Commit: ecf45080a4d3f4526cacb8b14060fe3b49a6913b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ecf45080a4d3f4526cacb8b14060fe3b49a6913b

Changed files:
  net/ipv4/sysctl_net_ipv4.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=ecf45080a4d3f4526cacb8b14060fe3b49a6913b

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

The original Linux kernel CVE announcement for CVE-2026-64002 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64002

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: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: 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).