[CVE-2026-97609][MODERATE REGULAR] netfilter: cttimeout: prevent UAF during module unload [ Upstream

[CVE-2026-97609][MODERATE REGULAR] netfilter: cttimeout: prevent UAF during module unload [ Upstream

[AL-KERNEL]

CVE: CVE-2026-97609
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: cttimeout: prevent UAF during module unload [ Upstream
Commit: a7fdd86c386b7f7cc72a126389c2cdb55d035221
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a7fdd86c386b7f7cc72a126389c2cdb55d035221
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97609
Analysis date: Fri, 25 Sep 2026 12:02:07 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97609 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97609

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.

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

CVE-2026-97609	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97609 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:H/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A use-after-free can occur during nfnetlink_cttimeout module unload because nf_ct_timeout_hook may remain reachable after the per net timeout data has been freed. A local attacker can race a netfilter timeout policy operation against module unload and cause ctnl_timeout_find_get to access freed memory. For the CVSS the PR:H is used because reliable triggering normally requires privileged netfilter rule management and module unload capabilities. The issue is not directly network reachable. The confirmed impact is local denial of service through a kernel crash. The use-after-free primitive may also permit confidentiality integrity and availability impact in the worst case and should be reviewed manually. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	REMOTE READ DANGER INIT NETFILTER UAF HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	YES	NO	checked

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

ActionableScore=1
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::

No floor applies. The Real UAF floor does not apply because complete reliable triggering requires host-admin-equivalent module unload capability.

2. Signal breakdown

Positive signals:

* +2 Real UAF or active lifetime violation. `cttimeout_exit()` frees per-net storage through `unregister_pernet_subsys()` while an RCU reader can still invoke `ctnl_timeout_find_get()` through the uncleared `nf_ct_timeout_hook`. KASAN directly reports slab use-after-free.
* +1 Reliable kernel crash or strong DoS. The stale per-net timeout-list access can cause a kernel fault or crash. This is counted once only.

Negative signals:

* -2 Full host-admin-equivalent privilege. Reliable self-triggering requires unloading the `nfnetlink_cttimeout` module. Module unload requires `CAP_SYS_MODULE` in the host initial user namespace. The concurrent netfilter operation additionally requires netfilter administration privileges.

Not awarded:

* No controlled reclaim or attacker-controlled replacement of the freed per-net object is demonstrated.
* No arbitrary or directed kernel write is demonstrated.
* No confidentiality or integrity impact is demonstrated.
* No remote reachability is established. The vulnerable operation is a local netfilter control-plane path.
* No concrete repeated release or refcount mutation exists. The stale operation is a read and list lookup through freed per-net storage, not a second `put`, `free`, or refcount decrement.
* No structured stale-object exploitation leverage is awarded. The available evidence shows a teardown-time stale read and lookup, not attacker-controlled post-free structured field consumption.
* No hard-race penalty is applied. Although this is a race, the supplied evidence does not establish an unusually rare or externally uncontrollable timing condition.
* No paranoid-only point is awarded. The patch proves a UAF read, but does not establish an additional post-free mutation, controlled reuse, disclosure, write primitive, or boundary bypass.

3. Reachability analysis

The vulnerable reader path is reached while validating an iptables target through `xt_ct_tg_check()`, `nf_ct_set_timeout()`, and the cttimeout hook. Adding or modifying the relevant netfilter rules normally requires `CAP_NET_ADMIN` for the target network namespace.

The free side is module exit in `cttimeout_exit()`. A reliable attacker-controlled trigger also needs to initiate module unload, which is a host-global action requiring `CAP_SYS_MODULE` in the initial user namespace. A network namespace capability is insufficient to unload a host kernel module.

NamespaceScopedPrivilege is therefore `NO`. Although netfilter rule operations can be namespace-scoped, the complete trigger includes host-global module unload and cannot be completed from an attacker-created network namespace alone.

No network packet path directly reaches the bug. The issue is triggered through local control-plane configuration and teardown activity. Repeated module load and unload cycles could make the race repeatable for a host administrator, but that does not create a lower-privileged attacker path.

4. Primitive and severity interpretation

The exact primitive is a confirmed RCU lifetime mismatch and use-after-free. The global `nf_ct_timeout_hook` still points to `ctnl_timeout_find_get()` after the corresponding per-net timeout storage has been freed. A concurrent RCU reader can call the stale hook and dereference the freed per-net timeout list.

This is an active structured per-net object, but the demonstrated stale use is limited to a teardown-time lookup and read. The patch does not show controlled object replacement, attacker-shaped reuse, callback dispatch from reclaimed memory, arbitrary read or write, or a second lifetime-mutating operation on the freed object.

This is `CLASS_B` because a real kernel UAF exists. It is nevertheless a constrained Class B case because the supplied evidence establishes primarily a crash-capable stale read during host-admin-controlled module unload. It is not `CLASS_A`.

The confirmed practical consequence is local kernel DoS. Confidentiality, integrity, privilege escalation, and controlled kernel corruption remain speculative and are not scored. `ImportantCandidate=NO` and `AutoDowngradeAllowed=YES` are appropriate because the UAF is constrained by a host-global privileged teardown operation and no meaningful post-free exploitation leverage is shown.

Likely operational severity is ordinary Moderate or lower-priority local kernel stability impact, depending on whether the product permits runtime unloading of this module.

5. One-sentence report phrase

A race during nfnetlink_cttimeout module unload can leave `nf_ct_timeout_hook` pointing to freed per-net timeout data, allowing a concurrent privileged netfilter policy operation to trigger a kernel use-after-free and local denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The issue is a confirmed kernel UAF, but the complete reliable trigger requires host-admin-equivalent module unload capability and the supplied evidence shows a stale read and crash path without controlled reuse, write, disclosure, or privilege-escalation leverage.

7. Call-site confidence

Call-site confidence: medium

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

Patch: netfilter: cttimeout: prevent UAF during module unload [ Upstream
Commit: a7fdd86c386b7f7cc72a126389c2cdb55d035221
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a7fdd86c386b7f7cc72a126389c2cdb55d035221

Changed files:
  net/netfilter/nfnetlink_cttimeout.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=a7fdd86c386b7f7cc72a126389c2cdb55d035221

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

The original Linux kernel CVE announcement for CVE-2026-97609 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97609

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:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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: unknown
  Paranoid ActionableScore: 1

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).