[CVE-2026-46319][IMPORTANT] net/sched: act_ct: Only release RCU read lock after ct_ft [ Upstream

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

CVE: CVE-2026-46319
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: net/sched: act_ct: Only release RCU read lock after ct_ft [ Upstream
Commit: ece578ca61e572df96cfc80456357ebfae0b4b9e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ece578ca61e572df96cfc80456357ebfae0b4b9e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46319
Analysis date: Mon, 06 Jul 2026 20:51:41 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in `net/sched act_ct` can free a `ct_ft` flow-table object after lookup but before its reference count is acquired, causing a use-after-free that may allow a local `CAP_NET_ADMIN` capable attacker to crash the kernel or potentially escalate privileges.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-46319 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46319

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: IMPORTANT
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-2026-46319	IMPORTANT	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-667;BEST CVSS score: '7';DESCR 'A race in net sched act_ct can leave a ct_ft pointer unprotected after rhashtable lookup and before the reference count is acquired. If cleanup runs in that window, the flow table object can be removed and freed, and the later refcount operation can access freed memory. This is a use-after-free condition in kernel control plane code and it may allow local privilege escalation or a kernel crash. For the CVSS the PR:L is selected because reliable triggering requires local ability to configure tc act_ct or equivalent CAP_NET_ADMIN access, which can be available to a reduced capability root, container root, or service account rather than full host root. The issue is not directly network reachable and is triggered by local traffic control configuration activity. Impact is at least local denial of service and in worst case full confidentiality, integrity, and availability impact due to a race based UAF primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) 	YES	REMOTE LOCK RACE UAF NETWORK LINUS KPANIC 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Generic memory corruption, strong corruption primitive: +2
  The patch fixes a real use-after-free where `ct_ft` can be freed before `refcount_inc_not_zero()` is executed.

* Strong LPE plausibility: +2
  The advisory explicitly states that the vulnerability can lead to privilege escalation, and the UAF involves a refcount operation on a freed kernel object, which is more concerning than a pure NULL dereference or crash-only bug.

* Real lifetime corruption: +1
  This is an RCU lifetime bug: lookup returns an object after the RCU read-side critical section has ended, leaving a stale pointer window before the reference is acquired.

* Reliable kernel crash / strong DoS: +1
  A UAF in this path can plausibly crash the kernel, even if privilege escalation is not achieved.

* Broad/default/common subsystem exposure: +1
  `net/sched` and `tc` actions are common kernel networking control-plane components, especially on container hosts and systems using traffic shaping or offload rules.

Subtracted signals:

* Hard or unreliable race / special timing required: -1
  The report notes that the race window is very short and required an artificial `msleep(100)` to make triggering easier.

* Requires CAP_NET_ADMIN or equivalent in typical deployments: -1 conservative
  Triggering typically requires the ability to configure `tc act_ct`. This is not ordinary unprivileged access, but it may be reachable by container root, delegated network administrators, or reduced-capability service accounts, so the full -2 root/admin penalty is not applied.

Paranoid difference:

* Paranoid score removes or weakens the privilege penalty because CAP_NET_ADMIN in a namespace or reduced-capability context is not equivalent to full host root, and the bug may cross a meaningful privilege boundary.

## 3. Reachability analysis

The bug is triggered locally through traffic control configuration involving `act_ct`, not by ordinary incoming network packets alone. A realistic attacker needs the ability to create or modify `tc` actions, usually requiring `CAP_NET_ADMIN` in the relevant network namespace.

Namespaces matter here. In typical host deployments this is privileged, but in containerized or delegated networking environments `CAP_NET_ADMIN` may be granted to a container root or service account that is not equivalent to full host root. That makes PR:L a defensible CVSS interpretation and prevents treating this as a fully admin-only non-issue.

The vulnerable path is not directly remote network reachable. However, it is in a common networking subsystem and involves a real RCU/refcount lifetime bug in kernel memory management.

Call-site confidence: high. The input includes the lookup path, the refcount acquisition point, the free path, and the patch that extends RCU protection across lookup and refcount acquisition.

## 4. Severity interpretation

This behaves more like an Important-class kernel vulnerability than an ordinary Moderate issue. The realistic exploitability is limited by the short race window and the need for `tc act_ct` configuration privileges. However, the primitive is a real UAF on a refcounted kernel object, and the advisory explicitly states potential privilege escalation.

The conservative view is Actionable Moderate / Important-candidate because the race is hard and no full exploit primitive is shown. The paranoid view reaches Strong Important candidate because refcount-after-free in a common kernel networking subsystem is historically dangerous and may be exploitable in reduced-privilege namespace scenarios.

## 5. One-sentence report phrase

A race in `net/sched act_ct` can free a `ct_ft` flow-table object after lookup but before its reference count is acquired, causing a use-after-free that may allow a local `CAP_NET_ADMIN` capable attacker to crash the kernel or potentially escalate privileges.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is a race-based UAF with an explicit privilege-escalation claim and a concrete RCU/refcount lifetime window. Even though the race is hard to trigger, it should not be auto-closed because namespace-delegated `CAP_NET_ADMIN` can make the practical privilege boundary weaker than full host root.

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

Patch: net/sched: act_ct: Only release RCU read lock after ct_ft [ Upstream
Commit: ece578ca61e572df96cfc80456357ebfae0b4b9e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ece578ca61e572df96cfc80456357ebfae0b4b9e

Changed files:
  net/sched/act_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=ece578ca61e572df96cfc80456357ebfae0b4b9e

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

The original Linux kernel CVE announcement for CVE-2026-46319 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46319

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: Not available
  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: 6
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).