[CVE-2026-52970][MODERATE 7.0] netfilter: nft_ct: fix missing expect put in obj eval

[CVE-2026-52970][MODERATE 7.0] netfilter: nft_ct: fix missing expect put in obj eval

[AL-KERNEL]

CVE: CVE-2026-52970
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: netfilter: nft_ct: fix missing expect put in obj eval
Commit: cdb9a25dd3416d427e8b2753210f8baf44207577
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cdb9a25dd3416d427e8b2753210f8baf44207577
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52970
Analysis date: Wed, 24 Jun 2026 15:47:54 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A missing `nf_ct_expect_put()` in `nft_ct_expect_obj_eval()` can leak conntrack expectation references when packets match nftables ct expectation rules, allowing network-driven resource exhaustion and denial of service in configured deployments.

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

The original Linux kernel CVE announcement for CVE-2026-52970 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52970

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.

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

CVE-2026-52970	MODERATE	CHECK	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-401;*CWE-772;**CWE-400;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_ct_expect_obj_eval() can allocate a conntrack expectation and call nf_ct_expect_related() without dropping the local reference. When an nftables ruleset uses ct expectation objects, packets that hit this rule path can repeatedly leak expectation references and consume conntrack resources. For the CVSS the PR:N is used because an attacker may only need network reachability to the affected packet path after the ruleset is already configured. The issue is network reachable only in deployments where nft_ct expectation rules are active and exposed to attacker controlled traffic. Impact is denial of service through resource exhaustion, usually limited at first but potentially high under sustained traffic.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE SIMPLEFIX NETFILTER KPANIC 	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

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

## 2. Signal breakdown

* Remote reachable / network-triggerable: +2
  Packets can hit `nft_ct_expect_obj_eval()` if an nftables ruleset with ct expectation objects is configured.
* Reliable kernel crash / strong DoS: +1
  The bug leaks conntrack expectation references and can cause resource exhaustion under repeated traffic.
* Common networking core path or packet-processing path: +1
  The affected logic is in netfilter packet evaluation, although the specific ct expectation feature is configuration-dependent.
* Availability impact realistic: +1 in paranoid scoring only
  Sustained attacker-controlled traffic may exhaust conntrack expectation resources and degrade or break connection tracking.
* No memory corruption bonus
  The patch fixes a missing `nf_ct_expect_put()` reference release. It indicates a reference/resource leak, not UAF, OOB write, double free, type confusion, or arbitrary write.
* No confidentiality or integrity bonus
  No evidence of data disclosure, credential access, object confusion, or write primitive is shown.

## 3. Reachability analysis

An attacker does not need privileges on the target host if the vulnerable nftables rule path is already configured and reachable by attacker-controlled packets. Creating or modifying such nftables rules normally requires `CAP_NET_ADMIN`, but triggering the leak after deployment can be network-driven. Namespaces or containers matter mainly for who can configure the rules, not for a remote packet sender hitting an already active rule path. This is not default exposure for all systems, because ct expectation objects must be configured, but it is still a realistic netfilter packet-path issue in affected deployments.

## 4. Severity interpretation

This behaves like an actionable Moderate resource-exhaustion vulnerability, not an Important memory-corruption issue. The theoretical impact is limited to DoS because the patch shows a missing reference drop rather than unsafe reuse or corruption of freed memory. The practical risk is higher than an ordinary local-only leak because the leak can be driven by network traffic when the relevant nftables expectation rule exists.

## 5. One-sentence report phrase

A missing `nf_ct_expect_put()` in `nft_ct_expect_obj_eval()` can leak conntrack expectation references when packets match nftables ct expectation rules, allowing network-driven resource exhaustion and denial of service in configured deployments.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because this is a network packet-path resource leak with configuration-dependent exposure, and affected systems running nftables ct expectation rules may be susceptible to sustained remote DoS.

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

Patch: netfilter: nft_ct: fix missing expect put in obj eval
Commit: cdb9a25dd3416d427e8b2753210f8baf44207577
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cdb9a25dd3416d427e8b2753210f8baf44207577

Commit description:

nft_ct_expect_obj_eval() allocates an expectation and may call
nf_ct_expect_related(), but never drops its local reference.

Add nf_ct_expect_put(exp) before return to balance allocation.

Fixes: 857b460 ("netfilter: nft_ct: add ct expectations support")
Cc: stable@vger.kernel.org
Signed-off-by: Li Xiasong <lixiasong1@huawei.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  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=cdb9a25dd3416d427e8b2753210f8baf44207577

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

The original Linux kernel CVE announcement for CVE-2026-52970 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52970

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: 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).