[CVE-2026-98794][MODERATE 7.0] ipvs: filter some flags received in the backup server [ Upstream

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

CVE: CVE-2026-98794
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ipvs: filter some flags received in the backup server [ Upstream
Commit: f4cd1db7d421e82945713a36084bb0c35b75b27e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f4cd1db7d421e82945713a36084bb0c35b75b27e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98794
Analysis date: Sat, 24 Oct 2026 07:45:53 -0400
ActionableScore: 6
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
Crafted IPVS synchronization flags can install inconsistent active connection state that is later consumed by backup-host lookup and traffic-processing paths.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98794 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98794

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-2026-98794	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98794 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	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:L/A:H';*CWE-20;CWE-345;CWE-436;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '7.1';DESCR 'This is an input validation and protocol logic flaw in the IPVS backup synchronization path. Crafted NO_CPORT and TEMPLATE flags can make normal connection lookups match a template, while ONE_PACKET can produce inconsistent handling of received connection records. For the CVSS the PR:N value is selected because a sender that can reach the IPVS synchronization channel does not need an authenticated IPVS account or local execution on the backup server. Reachability is normally adjacent because IPVS synchronization commonly uses a restricted multicast or cluster network. The demonstrated impact is corruption of synchronized connection state and disruption of traffic processing. No OOB access, UAF, arbitrary write, information leak, or proven privilege escalation primitive is established by the code change. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7.1 and the production ActionableScore returned 6 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP. The independent weaker Aegis shadow evaluated CVSS 4.3 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	MAYBE	REMOTE NETFILTER LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 6.
* Conservative score: 6; no floor or cap applied.
* Raw paranoid score: 6.
* Paranoid score: 6; unsupported memory-corruption or panic effects were not added.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 clearly network-reachable: an unauthenticated sender able to reach the configured IPVS synchronization channel can supply the flags.
* +1 weak/indirect active-state corruption: attacker-supplied `NO_CPORT|TEMPLATE` or `ONE_PACKET` flags were accepted into synchronized connection processing.
* +1 integrity plausible: malformed records can create inconsistent backup connection state, including normal lookups matching templates.
* +1 strong service DoS: supplied evidence supports disruption of traffic processing, though not a kernel panic.
* +1 practical chain: crafted synchronization record → corrupted connection semantics → later IPVS lookup/traffic-processing disruption.
* No OOB write, UAF, arbitrary write, disclosure, LPE, or reliable kernel crash is shown.
* NEW52 B5-R and NEW53 B3-PENDING do not apply: there is no heap OOB or shared-backing write.
* No authorization-decision bypass: this is validation of an intentionally unauthenticated synchronization protocol, not omission of a mandatory capability or access-control guard.

3. Reachability analysis

The assessed attacker is an adjacent-network sender with access to an already configured IPVS synchronization channel. No host UID, capability, namespace privilege, or authenticated IPVS account is needed for packet submission. Administrative setup is required to enable backup synchronization, but it is target deployment state rather than attacker privilege. Reachability is therefore below host administrator, although limited to networks exposing the synchronization multicast/channel. No race, special hardware, or retry sequence is involved.

4. Primitive and severity reading

The packet flags are used to create or update active structured IPVS connection state. That state is subsequently consumed by privileged backup-host lookup and packet-processing paths; specifically, `NO_CPORT|TEMPLATE` can cause ordinary connection lookups to hit template state. The trust boundary is the unauthenticated synchronization sender to the backup server’s kernel IPVS state.

This is CLASS_B semantic state corruption, not kernel memory corruption. Traffic disruption and connection-state integrity impact are supported; panic, host compromise, and arbitrary memory access are not. The concrete active-state write, later privileged consumer, and network trust boundary leave non-crash consequences requiring review, so automatic downgrade is unsafe.

5. One-sentence report phrase

Crafted IPVS synchronization flags can install inconsistent active connection state that is later consumed by backup-host lookup and traffic-processing paths.

6. Manual review advice

MANUAL CHECK REQUIRED

The active structured-state corruption crosses an unauthenticated synchronization boundary and has downstream privileged consumers, while its full operational impact remains unresolved.

7. Call-site confidence

Call-site confidence: medium

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

Patch: ipvs: filter some flags received in the backup server [ Upstream
Commit: f4cd1db7d421e82945713a36084bb0c35b75b27e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f4cd1db7d421e82945713a36084bb0c35b75b27e

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=f4cd1db7d421e82945713a36084bb0c35b75b27e

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

The original Linux kernel CVE announcement for CVE-2026-98794 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98794

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:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS score: 7.1

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: 6

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).