[CVE-2026-98419][MODERATE REGULAR] drop_monitor: fix out-of-bounds write in reset_per_cpu_data() [ Upstream

[CVE-2026-98419][MODERATE REGULAR] drop_monitor: fix out-of-bounds write in reset_per_cpu_data() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98419
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drop_monitor: fix out-of-bounds write in reset_per_cpu_data() [ Upstream
Commit: caf09c09e0f323015ab6777ed1bad5aa10688631
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=caf09c09e0f323015ab6777ed1bad5aa10688631
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98419
Analysis date: Wed, 14 Oct 2026 22:26:06 -0400
ActionableScore: 1
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-2026-98419 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98419

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.

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

CVE-2026-98419	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98419 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-787;CWE-131;CWE-193;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.6';DESCR 'An allocation size accounting error in reset_per_cpu_data causes memset to write 4 bytes beyond the netlink attribute payload and into skb_shared_info. The overwrite is limited to zero values at a fixed location, but it corrupts kernel networking metadata and may cause invalid SKB state, a kernel crash, or other availability failures. For the CVSS the PR:L value is used for the paranoid score because a user with delegated CAP_NET_ADMIN in a network namespace, container, or restricted network service may be able to configure drop_monitor without having full host administrator privileges. The issue is not confirmed as directly network reachable. Remote traffic may only influence the trigger indirectly when drop monitoring is already enabled and packet drops can be generated. Impact is at least denial of service and in the worst grounded case may include limited confidentiality or integrity impact due to the confirmed out-of-bounds write. Reliable privilege escalation is not demonstrated because the overwrite size, destination, and written value are fixed. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 6.6 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage IMPORTANT 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_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN5 and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4. The independent weaker Aegis shadow evaluated CVSS 2.4 and ActionableScore 0 with primitive class CLASS_B and manual review REQUIRED. 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 Ordinary Moderate (with actual score 1)	MAYBE	REMOTE WRITE OOB SKB HARDWARE  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN5 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 1.
* Conservative score: 1. No floor or cap applied.
* Raw paranoid score: 1.
* Paranoid score: 1. No additional consequence is sufficiently established.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Constrained kernel buffer overwrite. `memset()` performs a confirmed four-byte heap OOB write into the beginning of `skb_shared_info`.
* +0 Strong corruption primitive not awarded. The destination and length are fixed, and the payload consists only of zero bytes.
* +0 Memory-layout invariant not counted separately because it is the same allocation-size defect that causes the OOB write.
* +0 Reliable kernel crash not awarded. The commit establishes metadata corruption but does not demonstrate a panic or another fatal consequence.
* +0 Networking exposure not awarded. `drop_monitor` is a specialized monitoring path, and direct packet-triggered reachability without prior configuration is not established.
* No negative point was applied for the fixed payload and target because that limitation is already reflected by using constrained overwrite +1 rather than strong corruption +2.
* Controlled target selection, arbitrary write, controlled reclaim, disclosure, privilege escalation, and authorization bypass are not demonstrated.
* No UAF, repeated release, refcount mutation, or lifetime violation exists.
* B5-R does not apply. There is no retry-accumulated index or offset, no missing retry reset, and no evidence of attacker-influenced accumulation across re-entry.
* B3-PENDING does not apply because no shared file-backed or cross-authority backing-store write is established.
* B4-PENDING does not apply because the patch does not alter an authorization decision.

3. Reachability analysis

The vulnerable operation executes while preparing a generic-netlink alert in `drop_monitor`. The supplied context does not establish whether an attacker can independently enable and configure the monitor, set the relevant parameters, and drive the complete alert-generation path below host-admin privilege.

CAP_NET_ADMIN may be involved in configuration, but the evidence does not identify the exact user namespace governing every required operation. Therefore host-admin and namespace-scoped reachability remain unknown. Remote traffic might generate packet-drop events after separate monitor configuration, but that does not establish direct remote triggerability or eliminate the prior setup requirement.

No retry race, special hardware, boot option, or attacker-controlled allocation sequence is shown.

4. Primitive and severity interpretation

The exact primitive is a four-byte heap OOB zero write from the netlink attribute payload into the adjacent `skb_shared_info`. This is real kernel memory corruption, but it is constrained by a fixed destination, fixed size, and fixed value.

The affected SKB is subsequently used by the netlink path, but the supplied evidence does not show that the overwritten bytes contain nonzero active state at that point or that their consumption produces a crash, disclosure, directed corruption, or security-boundary consequence. In a newly allocated SKB, the leading `skb_shared_info` bookkeeping fields may already be initialized to zero, further limiting demonstrated leverage without making the spatial violation nonexistent.

This is CLASS_B rather than CLASS_A because an actual overwrite exists but no attacker-directed target, payload, active-object replacement, or useful post-corruption behavior is established. It is not CLASS_C because the defect is a confirmed write outside the allocated payload rather than only an invalid-state warning or dereference.

ImportantCandidate is NO because the NEW52 B5-R chain and other Important-preserving mechanisms are absent. AutoDowngradeAllowed is YES because no meaningful unresolved exploitation primitive beyond the constrained overwrite is established. Operational severity is most consistent with an ordinary Moderate or hardening defect, subject to confirmation of the exact `skb_shared_info` layout and trigger permissions.

5. One-sentence report phrase

A netlink allocation accounting error causes a fixed four-byte zero overwrite into `skb_shared_info`, but no attacker-directed corruption, reliable crash, disclosure, or privilege-escalation primitive is currently established.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm the affected kernel layout, whether the overwritten `skb_shared_info` fields can hold active nonzero state, and whether the complete `drop_monitor` trigger is available below host-admin privilege.

7. Call-site confidence

Call-site confidence: medium

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

Patch: drop_monitor: fix out-of-bounds write in reset_per_cpu_data() [ Upstream
Commit: caf09c09e0f323015ab6777ed1bad5aa10688631
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=caf09c09e0f323015ab6777ed1bad5aa10688631

Changed files:
  net/core/drop_monitor.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=caf09c09e0f323015ab6777ed1bad5aa10688631

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

The original Linux kernel CVE announcement for CVE-2026-98419 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98419

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.6

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: 1

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).