[CVE-2026-98010][LOW] net/sched: drr: clamp quantum in change class [ Upstream

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

CVE: CVE-2026-98010
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net/sched: drr: clamp quantum in change class [ Upstream
Commit: dc8b374214ef5bba4882bbd95b361e42555cfc0d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dc8b374214ef5bba4882bbd95b361e42555cfc0d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98010
Analysis date: Mon, 28 Sep 2026 15:26:17 -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-2026-98010 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98010

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-2026-98010	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98010 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-400;CWE-834;CWE-770;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'The DRR scheduler can perform an excessive number of deficit refill iterations when a class has a very small quantum and a crafted size table produces a packet length close to 2 GiB. The loop runs while holding the qdisc lock and can consume a CPU for a prolonged period, block queue processing, and potentially cause a soft lockup or wider loss of system responsiveness. For the CVSS the PR:L value is used because CAP_NET_ADMIN is required in the affected network namespace, but an unprivileged local user may obtain this capability through a new user and network namespace when unprivileged user namespaces are enabled. The issue is not directly network reachable because remote packet traffic alone cannot install the required qdisc configuration. Impact is denial of service only. No UAF, out of bounds access, information leak, or write primitive is supported by the affected code.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) 	MAYBE	REMOTE DANGER SIMPLEFIX NETWORK HARDWARE QDISC  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2
PrimitiveClass=NONE
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
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +1 Local unprivileged trigger. The supplied evidence explicitly states that namespace-local CAP_NET_ADMIN obtained through `unshare -Urn` is sufficient for the complete qdisc configuration.
* +1 Reliable strong DoS. A crafted size table and very small quantum can cause an extremely long deficit-refill loop while the qdisc lock is held, potentially producing a CPU soft lockup and degraded host responsiveness.

No negative points were applied.

Important non-awarded signals:

* No corruption primitive was awarded. The defect causes excessive iteration, not UAF, OOB access, stale-object use, or a kernel write.
* No extra availability point was awarded because CPU lockup and stalled queue processing are the same DoS consequence.
* No remote-reachability point was awarded because network traffic alone cannot install the required DRR configuration.
* No common networking data-path point was awarded because this is an explicitly configured DRR control-plane condition, not a broadly exercised default packet path.
* No confidentiality, integrity, LPE, authorization-bypass, or isolation-bypass point was awarded.
* No race penalty applies because the trigger is deterministic and does not depend on a timing window.
* `CONFIG_NET_SCH_DRR` was not treated as a rare-configuration penalty because the attacker can instantiate the qdisc in the reachable namespace.

3. Reachability analysis

An ordinary local user can reach the supplied trigger when unprivileged user namespaces are enabled. `unshare -Urn` creates attacker-owned user and network namespaces and grants CAP_NET_ADMIN within that network namespace. The attacker can then create a namespace-local device and configure the DRR qdisc, class, quantum, and size table needed for the excessive loop.

The relevant privilege is namespace-scoped CAP_NET_ADMIN, and the input explicitly establishes that the complete trigger works in the attacker-created namespace. No separate host-administrator setup, physical hardware, special device, race, or remote packet source is required. If unprivileged user namespaces are disabled, this below-host-admin path may be unavailable, but that deployment restriction does not negate the positively established namespace-scoped path.

4. Primitive and severity interpretation

The exact defect is an insufficiently bounded DRR quantum that permits algorithmically excessive deficit-refill iterations under the qdisc lock. It is a deterministic CPU-exhaustion and lock-hold DoS rather than memory corruption or a lifetime violation.

There is no active or fixed stale storage, no repeated release or refcount mutation, and no attacker-controlled overwrite. The demonstrated consequence is prolonged CPU consumption, blocked qdisc processing, and possible soft lockup. A stronger confidentiality, integrity, or privilege-escalation consequence is unsupported.

`PrimitiveClass=NONE` is appropriate because no corruption, ownership, authorization, or comparable security primitive is established. `ImportantCandidate=NO` and `AutoDowngradeAllowed=YES` follow because this is a bounded bug class with DoS-only consequences and no unresolved exploitation leverage.

5. One-sentence report phrase

A local unprivileged user with attacker-obtainable namespace-scoped CAP_NET_ADMIN can configure a DRR qdisc with a very small quantum and crafted packet accounting to cause excessive CPU iteration under the qdisc lock, resulting in denial of service without memory corruption.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a deterministic namespace-local CPU DoS with no UAF, overwrite, disclosure, authorization bypass, or unresolved Important-grade primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: net/sched: drr: clamp quantum in change class [ Upstream
Commit: dc8b374214ef5bba4882bbd95b361e42555cfc0d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dc8b374214ef5bba4882bbd95b361e42555cfc0d

Changed files:
  net/sched/sch_drr.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=dc8b374214ef5bba4882bbd95b361e42555cfc0d

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

The original Linux kernel CVE announcement for CVE-2026-98010 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98010

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:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  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).