[CVE-2026-98011][LOW] net/sched: hhf: clamp quantum in change and init paths [ Upstream

[CVE-2026-98011][LOW] net/sched: hhf: clamp quantum in change and init paths [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98011
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net/sched: hhf: clamp quantum in change and init paths [ Upstream
Commit: 1113b674307ffddd402524bd1fd9d7d5629b705b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1113b674307ffddd402524bd1fd9d7d5629b705b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98011
Analysis date: Sat, 26 Sep 2026 15:19:53 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98011 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98011

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: LOW
Manual review required: NO

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

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

CVE-2026-98011	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98011 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-835;**CWE-400;CWE-770;BEST CVSS score: '5.5';DESCR 'The supplied source contains only the abbreviated commit identifier eb56a49. Base and paranoid scores are identical because this is a deterministic resource consumption DoS with no supported path to memory corruption or privilege escalation. Verify whether CONFIG_NET_SCH_HHF is enabled and whether HHF qdiscs are used before prioritizing remediation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	REMOTE DEADLOCK DANGER SIMPLEFIX NETWORK QDISC  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

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

1. ActionableScore

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

2. Signal breakdown

* +1 Reliable denial of service. A quantum value of 1 combined with the crafted size table causes approximately 2^31 deficit refill iterations while holding the qdisc lock, resulting in a CPU soft lockup.
* +1 Local unprivileged trigger. The supplied commit explicitly states that CAP_NET_ADMIN in an attacker-created user and network namespace is sufficient through unshare -Urn.
* +0 No memory-corruption primitive. The patch clamps a numeric scheduling parameter and does not establish UAF, double free, OOB access, stale pointer use, refcount misuse, or an arbitrary write.
* +0 No confidentiality or integrity impact. The demonstrated effect is CPU consumption and qdisc lock retention only.
* +0 No remote reachability. Normal network packets do not reach the vulnerable control-plane configuration path.
* +0 No extra availability point. The soft lockup is the same demonstrated DoS consequence already counted above.
* No configuration penalty applied. CONFIG_NET_SCH_HHF must be enabled, but the vulnerable HHF qdisc can be instantiated by the attacker once that feature is available. This is not a host-admin-only prior setup requirement under the supplied conditions.
* No race penalty applied. This is deterministic excessive iteration caused by attacker-controlled configuration, not a timing race.

3. Reachability analysis

The attacker is a local ordinary user who can create a user namespace and network namespace. The supplied commit explicitly states that unshare -Urn provides sufficient namespace-local CAP_NET_ADMIN and that the complete reproducer can create and modify an HHF qdisc with quantum set to 1.

The relevant qdisc and rtnetlink capability checks are namespace-scoped for this supplied attack scenario. A dummy network device and the qdisc can be managed in the attacker-controlled network namespace. Therefore host-admin-equivalent privilege is not required and NamespaceScopedPrivilege is YES.

The prerequisite is that CONFIG_NET_SCH_HHF is enabled in the running kernel. No special hardware, firmware interaction, network exposure, race condition, or prior host-created network topology is required by the supplied reproducer.

4. Primitive and severity interpretation

The exact primitive is an attacker-controlled low quantum value that creates an excessively large deficit refill loop under the qdisc lock. This is an algorithmic complexity and resource-consumption issue, not a memory safety or lifetime issue.

There is no active stale object, fixed stale storage, UAF, refcount mutation, ownership violation, authorization bypass, or semantic reinterpretation. The demonstrated consequence is a CPU soft lockup and denial of service affecting packet scheduling and potentially host responsiveness. A privilege escalation, information disclosure, integrity violation, or controlled kernel corruption path is not supported by the patch context.

PrimitiveClass is CLASS_C because the issue is a demonstrated invalid-state DoS condition. ImportantCandidate is NO and AutoDowngradeAllowed is YES because there is no unresolved memory-corruption or security-boundary primitive requiring preservation for manual exploitation analysis. Operational priority should depend on whether HHF qdiscs are enabled and usable in the target environment.

5. One-sentence report phrase

An unprivileged local user can configure an HHF qdisc with quantum set to 1 in an attacker-controlled network namespace, causing a large deficit refill loop under the qdisc lock and resulting in CPU soft lockup denial of service.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The vulnerability is a deterministic namespace-reachable local resource-consumption DoS with no established memory corruption, lifetime violation, confidentiality impact, integrity impact, or privilege-escalation primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: net/sched: hhf: clamp quantum in change and init paths [ Upstream
Commit: 1113b674307ffddd402524bd1fd9d7d5629b705b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1113b674307ffddd402524bd1fd9d7d5629b705b

Changed files:
  net/sched/sch_hhf.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=1113b674307ffddd402524bd1fd9d7d5629b705b

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

The original Linux kernel CVE announcement for CVE-2026-98011 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98011

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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).