[CVE-2026-98857][MODERATE REGULAR] ipvs: bound LBLCR and LBLC cache growth [ Upstream

[CVE-2026-98857][MODERATE REGULAR] ipvs: bound LBLCR and LBLC cache growth [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98857
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ipvs: bound LBLCR and LBLC cache growth [ Upstream
Commit: 31028d7b970962fbeda1e9131405c76551094300
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=31028d7b970962fbeda1e9131405c76551094300
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98857
Analysis date: Mon, 19 Oct 2026 03:17:23 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A remote attacker reaching an IPVS service configured with LBLC or LBLCR may sustain cache growth with many active destination addresses and eventually cause denial of service through kernel memory exhaustion.

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

The original Linux kernel CVE announcement for CVE-2026-98857 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98857

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-98857	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98857 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=3 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	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-400;CWE-770;CWE-789;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.9';DESCR 'The IPVS LBLC and LBLCR schedulers can create a cache entry for every previously unseen destination address without enforcing max_size at allocation time. The periodic collector starts reclaiming entries only after the table has exceeded that limit and cannot reclaim entries that an attacker continues to use. A remote attacker who can reach a virtual service configured with one of these schedulers and influence many destination addresses may sustain traffic that causes continued kernel memory growth. For the CVSS the PR:N value is used because no authenticated account or local execution context is required when the affected IPVS service is reachable over the network. AC:H reflects the need for a specific IPVS scheduler and routing configuration together with sustained traffic and control over many destination addresses. Impact is resource exhaustion and denial of service. No UAF, OOB access, arbitrary write, information disclosure, or privilege escalation primitive is supported by the allocation and cache management paths. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.9 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 5.9 and ActionableScore 3 with primitive class CLASS_C and manual review RECOMMENDED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	REMOTE SIMPLEFIX NETFILTER LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative signals:

* +2 Remote reachable. The commit explicitly describes attacker-maintained cache entries created from previously unseen destination addresses. Once an IPVS service using LBLC or LBLCR is deployed and reachable, the attacker does not need local execution or administrative credentials.
* No crash point was added conservatively. The patch establishes unbounded cache growth but does not demonstrate how much traffic or memory is required for a host-wide failure.

Paranoid additional signal:

* +1 Strong resource-exhaustion DoS. Sustained creation and reuse of distinct destination entries can prevent collection and continue consuming kernel memory, making eventual severe memory pressure or host-wide availability loss technically credible.

Not awarded:

* No persistent-reference-leak point. Entries remain reachable through the cache and can be collected. This is uncontrolled growth rather than a lost reference.
* No UAF, OOB access, overwrite, stale-object use, authorization bypass, shared-backing write, or structured-state corruption is established.
* B5-R does not apply because there is no heap OOB write or retry-accumulated write offset.
* B3-PENDING does not apply because no shared or file-backed storage is modified.
* V33 and V34 do not apply because no attacker-influenced active structured state is corrupted.
* No confidentiality, integrity, privilege-escalation, controlled-reclaim, or arbitrary-write signal is supported.
* No extra availability point was added beyond the paranoid resource-exhaustion consequence.
* No rarity or host-admin penalty was applied merely because LBLC or LBLCR requires prior administrative service configuration.

3. Reachability analysis

The evaluated attacker is a remote network peer that can send traffic to an already configured IPVS virtual service using the LBLC or LBLCR scheduler. The attacker must be able to cause lookups for many previously unseen destination addresses and keep entries active long enough to defeat periodic reclamation.

Configuring IPVS and selecting these schedulers requires prior administrative setup, but the remote attacker does not need to perform that setup. No local capability, host UID 0, or namespace-scoped privilege is required for the subsequent packet-driven trigger. The path is configuration-dependent and requires sustained traffic, but it is not a timing race and does not require special hardware.

4. Primitive and severity interpretation

The exact defect is missing allocation-time enforcement of the cache size limit. The tables may continue allocating valid cache objects after exceeding `max_size`, while entries kept active by traffic remain ineligible for collection.

This is resource exhaustion without memory corruption. It is not a persistent reference leak, UAF, OOB write, or authorization flaw. The demonstrated consequence is continued kernel-memory growth. A severe host-wide DoS is credible under sustained abuse but is not shown as immediate or achievable with a small number of requests.

`PrimitiveClass=NONE` is appropriate because no corruption, lifetime, ownership, or security-boundary primitive exists. `ImportantCandidate=NO` and `AutoDowngradeAllowed=YES` follow because the issue remains an ordinary resource-exhaustion class without an isolation bypass or stronger primitive. Manual review is recommended because practical exposure and exhaustion rate depend on routing, scheduler configuration, address control, entry size, and traffic sustainability.

5. One-sentence report phrase

A remote attacker reaching an IPVS service configured with LBLC or LBLCR may sustain cache growth with many active destination addresses and eventually cause denial of service through kernel memory exhaustion.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm that LBLC or LBLCR is deployed, determine whether untrusted traffic can influence destination addresses, and measure whether realistic traffic can cause host-wide exhaustion.

7. Call-site confidence

Call-site confidence: medium

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

Patch: ipvs: bound LBLCR and LBLC cache growth [ Upstream
Commit: 31028d7b970962fbeda1e9131405c76551094300
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=31028d7b970962fbeda1e9131405c76551094300

Changed files:
  net/netfilter/ipvs/ip_vs_lblc.c
  net/netfilter/ipvs/ip_vs_lblcr.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=31028d7b970962fbeda1e9131405c76551094300

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

The original Linux kernel CVE announcement for CVE-2026-98857 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98857

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: 2
  Paranoid ActionableScore: 3

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).