[CVE-2026-74347][MODERATE 7.0] netfilter: cttimeout: detach dataplane timeout policy and repurpose refcount [ Upstream

[CVE-2026-74347][MODERATE 7.0] netfilter: cttimeout: detach dataplane timeout policy and repurpose refcount [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74347
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: cttimeout: detach dataplane timeout policy and repurpose refcount [ Upstream
Commit: 9aeb0dcfeb460d33d61d434148b51103ab1d2013
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9aeb0dcfeb460d33d61d434148b51103ab1d2013
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74347
Analysis date: Sun, 16 Aug 2026 07:40:13 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A netfilter cttimeout lifetime bug can leave conntrack dataplane entries referencing a timeout policy after control-plane removal, creating a plausible UAF condition with at least local DoS impact and requiring manual review for potential privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74347 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74347

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-2026-74347	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-416;*CWE-664;CWE-362;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A lifetime bug in netfilter cttimeout can leave dataplane conntrack entries holding references to a timeout policy after the policy is removed from the control plane. Existing conntrack entries or packets delayed in nfqueue may continue to carry the timeout extension until reinjection or conntrack cleanup, creating a plausible use-after-free condition when the timeout object is freed too early. For the CVSS the PR:L is used because reliable triggering normally requires the ability to configure or delete conntrack timeout policy through CAP_NET_ADMIN, which may be available to container root or delegated network administration contexts rather than full host root. The issue is not directly network reachable as a standalone packet-only attack, although network traffic can help create or keep affected conntrack entries alive once a vulnerable policy is configured. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to use-after-free memory corruption and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	REMOTE LOCK INIT NOMEMCHK NETFILTER RACE SKB PACKET  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	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: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Memory corruption, weak or indirect corruption candidate: +1. The patch fixes a stale lifetime model where conntrack timeout extensions may retain pointers after control-plane policy removal.
* Real lifetime corruption: +1. The change moves refcounting to `struct nf_ct_timeout` and drops references when conntracks are freed, which strongly indicates an object lifetime or RCU lifetime bug.
* Reliable kernel crash / strong DoS: +1. A stale timeout pointer in conntrack dataplane use can plausibly lead to UAF dereference or crash.
* Common networking / netfilter relevance: +1. This is in netfilter conntrack timeout handling, with dataplane conntrack entries involved after policy setup.
* Weak LPE concern in paranoid score: +1. UAF in kernel networking lifetime management can sometimes become exploitable, but no controlled reclaim, write primitive, callback control, or type confusion is shown.
* Requires CAP_NET_ADMIN or equivalent control-plane access: -1 in practical triage. Full host root is not necessarily required in all deployments because container root or delegated network administration may have relevant capabilities, so I do not apply the full -2 penalty.

No remote-reachable bonus is applied. Packet traffic can help keep conntrack entries alive, but the vulnerable sequence requires prior timeout policy configuration or deletion through netfilter control plane.

## 3. Reachability analysis

Triggering appears to require local ability to create or remove conntrack timeout policies via nfnetlink or nftables and to create conntrack entries using that policy. In typical deployments this requires CAP_NET_ADMIN, but namespace or container delegation can lower the practical privilege boundary from full host root to a reduced-privilege administrative context.

The issue is not a pure packet-only remote attack. Remote traffic may influence conntrack lifetime after a vulnerable policy is configured, but policy manipulation is the key trigger. The affected subsystem is not always configured, but netfilter and conntrack are common enough that this should not be treated as a rare driver-only issue.

## 4. Severity interpretation

This is above ordinary Moderate because the patch fixes dataplane lifetime ownership of an object referenced from conntrack extensions, not just validation or cleanup style. Realistically, the most supported impact is local DoS through a stale pointer or UAF crash. Theoretical privilege escalation is plausible enough for manual review because this is a kernel UAF/refcount/RCU lifetime bug in networking, but the patch does not show a strong exploit primitive such as controlled reclaim, arbitrary write, callback hijack, or type confusion.

## 5. One-sentence report phrase

A netfilter cttimeout lifetime bug can leave conntrack dataplane entries referencing a timeout policy after control-plane removal, creating a plausible UAF condition with at least local DoS impact and requiring manual review for potential privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a refcount and RCU lifetime redesign around `struct nf_ct_timeout` used by conntrack dataplane entries. Even though the realistic trigger needs CAP_NET_ADMIN-like access and no strong LPE primitive is demonstrated, the UAF class and netfilter dataplane involvement make auto-close unsafe.

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

Patch: netfilter: cttimeout: detach dataplane timeout policy and repurpose refcount [ Upstream
Commit: 9aeb0dcfeb460d33d61d434148b51103ab1d2013
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9aeb0dcfeb460d33d61d434148b51103ab1d2013

Changed files:
  include/net/netfilter/nf_conntrack_timeout.h
  net/netfilter/nf_conntrack_core.c
  net/netfilter/nf_conntrack_timeout.c
  net/netfilter/nfnetlink_cttimeout.c
  net/netfilter/nft_ct.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=9aeb0dcfeb460d33d61d434148b51103ab1d2013

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

The original Linux kernel CVE announcement for CVE-2026-74347 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74347

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: 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: 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).