[CVE-2026-97596][MODERATE REGULAR] ipvs: reject invalid states in connection template sync records

[CVE-2026-97596][MODERATE REGULAR] ipvs: reject invalid states in connection template sync records

[AL-KERNEL]

CVE: CVE-2026-97596
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ipvs: reject invalid states in connection template sync records
Commit: fc10dc4511e6e2e2b4098ee115c8e5639471f23d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fc10dc4511e6e2e2b4098ee115c8e5639471f23d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97596
Analysis date: Fri, 25 Sep 2026 11:59:03 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
An IPVS sync receiver can accept an invalid connection-template state and later use it as a TCP or SCTP transition-table index, allowing a network-adjacent attacker with access to the IPVS synchronization channel to cause invalid kernel state handling or possible denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-97596 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97596

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.

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

CVE-2026-97596	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97596 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-129;CWE-125;*CWE-20;BEST CVSS score: '6.5';DESCR 'An IPVS sync receiver can store an invalid state from a connection template sync record because template states were logged but not rejected. The invalid state can later be used as an index in TCP or SCTP connection state transition tables after ordinary connection lookup. This may cause an out of bounds read and can result in a kernel crash or other denial of service condition. For the CVSS the PR:N because no local user access is required when an attacker can transmit crafted IPVS synchronization traffic to the target. The attack vector is AV:A because IPVS sync is normally deployed on a dedicated multicast or trusted load balancer network and is not usually exposed to the public Internet. No confidentiality or integrity impact is assigned because the patch supports an invalid table index and possible out of bounds read but does not demonstrate a memory disclosure or write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	REMOTE SIMPLEFIX NETFILTER IPV6  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	YES	NO	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap was applied.

## 2. Signal breakdown

* +2 Directly network-triggerable: An attacker able to transmit IPVS synchronization records to an active IPVS sync receiver can provide an invalid template state. No local code execution or host administrative privilege is needed by that attacker once the receiver is deployed and reachable.
* +0 Weak corruption concern: The state reaches TCP or SCTP transition-table indexing outside its valid template-state range. This is an invalid index and possible out-of-bounds read, but the supplied patch does not establish an attacker-controlled write, controlled object replacement, or post-read data disclosure.

Important non-awarded signals:

* Controlled reclaim is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated.
* Real UAF, refcount misuse, double free, or another lifetime violation is not demonstrated.
* Confidentiality is not awarded because no kernel memory content is copied back to the attacker or otherwise disclosed.
* Integrity is not awarded because the patch does not establish modification of protected kernel state, credentials, policy, or another principals data.
* Reliable kernel crash is not separately awarded. The invalid table index can plausibly destabilize protocol state handling, but the patch does not show a panic, Oops, or a deterministic crash path.
* Common networking-core exposure is not awarded. IPVS synchronization is a specialized load-balancer replication feature, not ordinary TCP receive processing for general hosts.
* No privilege penalty is applied. The vulnerable receive path is network reachable when IPVS sync is active, and there is no evidence that the remote sender needs host-admin-equivalent privilege.
* No niche-subsystem penalty is applied. IPVS sync deployment is a precondition for exposure, but the supplied evidence does not show that the attacker must perform privileged local setup.

## 3. Reachability analysis

The evaluated attacker is a network-adjacent attacker able to send crafted IPVS synchronization traffic to a host configured as an IPVS sync receiver. The IPVS sync protocol is normally used between load balancer peers, commonly over a multicast or otherwise restricted synchronization network.

The complete vulnerable operation does not require local attacker code execution after the receiver is active. Therefore HostAdminRequired is NO for the triggering attacker model. This does not mean that IPVS setup itself is unprivileged. A separate administrator normally configures IPVS and enables synchronization, but that setup is a deployment precondition rather than an attacker capability required for packet delivery.

NamespaceScopedPrivilege is UNKNOWN. The supplied patch does not show the relevant network namespace ownership, whether sync traffic can be delivered into an attacker-controlled namespace, or whether all required IPVS sync setup is namespace-scoped.

There is no race requirement. The malformed state is accepted deterministically by the affected receiver paths before the fix.

## 4. Primitive and severity interpretation

The exact primitive is insufficient validation of an attacker-controlled connection-template state followed by later use of that state as an index into TCP or SCTP transition tables.

This is not a UAF, stale-reference, refcount, ownership, or COW issue. It is an invalid-state and possible read-only out-of-bounds indexing issue. The patch changes behavior from logging an invalid template state and continuing to rejecting that record before connection lookup or modification.

The supplied evidence does not establish that the out-of-range lookup provides useful attacker-controlled data, disclosure, a write primitive, structured object reinterpretation, callback control, or privilege escalation. The likely practical consequence is malformed connection state handling or a possible denial of service in an exposed IPVS synchronization deployment.

PrimitiveClass is CLASS_C because the demonstrated behavior is invalid-state processing with a possible out-of-bounds read, without an independently useful corruption primitive. ImportantCandidate is NO because meaningful exploitation leverage beyond protocol disruption or possible DoS is not established. AutoDowngradeAllowed is YES because no unresolved UAF, write primitive, security-boundary bypass, or active-object corruption mechanism is shown.

## 5. One-sentence report phrase

An IPVS sync receiver can accept an invalid connection-template state and later use it as a TCP or SCTP transition-table index, allowing a network-adjacent attacker with access to the IPVS synchronization channel to cause invalid kernel state handling or possible denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The issue is reachable through network-delivered IPVS synchronization records in configured deployments, but the supplied patch establishes only invalid-state handling and possible out-of-bounds reads, not a demonstrated write, disclosure, UAF, or privilege-escalation primitive.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: ipvs: reject invalid states in connection template sync records
Commit: fc10dc4511e6e2e2b4098ee115c8e5639471f23d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fc10dc4511e6e2e2b4098ee115c8e5639471f23d

Commit description:

IPVS sync receivers validate protocol states before creating or updating a
connection. For connection templates, however, they only log states outside
the template state range and still store the value in the connection.

A template can be returned by ordinary connection lookup. TCP and SCTP then
use the invalid state as an index into their transition tables.

Reject invalid template states in both sync protocol versions before
looking up or modifying a connection. The version 1 path handles both
IPv4 and IPv6 records.

Fixes: 2754114 ("ipvs: add assured state for conn templates")
Cc: stable@vger.kernel.org
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Kyle Zeng <kylebot@openai.com>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/netfilter/ipvs/ip_vs_sync.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=fc10dc4511e6e2e2b4098ee115c8e5639471f23d

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

The original Linux kernel CVE announcement for CVE-2026-97596 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97596

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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 6.5

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: 2

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).