[CVE-2026-98495][MODERATE REGULAR] net: arp: terminate device name before lookup

[CVE-2026-98495][MODERATE REGULAR] net: arp: terminate device name before lookup

[AL-KERNEL]

CVE: CVE-2026-98495
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: arp: terminate device name before lookup
Commit: ae6d704dbf9542b0a0830ec91a2db4f30307e7d8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae6d704dbf9542b0a0830ec91a2db4f30307e7d8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98495
Analysis date: Fri, 23 Oct 2026 21:32:10 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A locally supplied unterminated ARP device name can make alternative interface lookup read beyond a stack field, with a possible limited comparison oracle but no demonstrated write, crash or privilege escalation primitive.

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

The original Linux kernel CVE announcement for CVE-2026-98495 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98495

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-2026-98495	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98495 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 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:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';CWE-170;CWE-125;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '3.3';DESCR 'The ARP ioctl accepts a userspace struct arpreq whose arp_dev field can contain IFNAMSIZ bytes without a terminating NUL. Device lookup can pass this field to strcmp while resolving an alternative interface name, allowing the comparison to read beyond arp_dev and into adjacent kernel stack data. The issue is locally reachable through socket ioctls and is not triggered directly by network packets. A suitably matching alternative interface name is required for the comparison to cross the field boundary, so the conservative vector uses AC:H. For the CVSS the PR is L in the highest score paranoid vector because an unprivileged local process can normally issue SIOCGARP, even though ARP modification operations require CAP_NET_ADMIN. The established primitive is an OOB stack read with no write primitive. Impact is potentially a limited confidentiality oracle, but useful disclosure, kernel crash and privilege escalation are not proven. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 3.3 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 CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class 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_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 1 with primitive class CLASS_C 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 Borderline / manual review recommended (with actual score 3)	MAYBE	REMOTE OOB SIMPLEFIX NETWORK HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
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
* Conservative CVSS: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N 2.5 LOW
* Highest defensible paranoid CVSS: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N 3.3 LOW
* No floor or cap changed either score.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* Positive 1: A local user controls all IFNAMSIZ bytes of arp_dev and can omit the required NUL terminator.
* Positive 1: The supplied call path establishes a kernel stack OOB read through device name lookup and strcmp.
* Paranoid positive 1: Lookup success, failure or timing may form a limited comparison oracle influenced by adjacent stack bytes. A useful disclosure channel is not demonstrated.
* Negative 0: A matching alternative interface name is required before comparison crosses the arp_dev boundary. This supports AC:H for the conservative CVSS but is not treated as an unsupported privilege penalty.
* Negative 0: No OOB write, UAF, refcount mutation, callback dispatch, controlled reclaim or arbitrary kernel access is established.
* Negative 0: No kernel bytes are directly copied to userspace or transmitted over the network.
* Negative 0: No reliable kernel crash, privilege escalation or authorization bypass is demonstrated.
* Not awarded: Remote reachability. Network packets do not populate the userspace struct arpreq passed to this ioctl.
* Not awarded: Common packet processing path. This is a local ARP control interface rather than ordinary receive processing.
* Not awarded: Confidentiality beyond C:L. The only plausible effect is a constrained comparison oracle.
* B5-R does not apply because there is no heap OOB write or retry accumulated offset.
* B3-PENDING does not apply because no shared backing write exists.
* B4-PENDING does not apply because no authorization decision changes from DENY to ALLOW.

3. Reachability analysis

The vulnerable path is reached through an ARP socket ioctl that copies a userspace struct arpreq into the stack object r. SIOCGARP is ordinarily available to a local unprivileged process, while SIOCSARP and SIOCDARP require CAP_NET_ADMIN. Therefore HostAdminRequired is NO and RequiresHostUID0 is NO for the read path.

For the CVSS the PR is L because exploitation requires a local process and invocation of the ioctl interface. PR:N would incorrectly describe a trigger requiring no local user or process context.

The relevant call path is arp_ioctl, copy_from_user, dev_get_by_name_rcu or __dev_get_by_name, alternative interface name lookup and strcmp. The attacker supplies an arp_dev field containing IFNAMSIZ nonzero bytes. A suitably matching alternative interface name must exist for comparison to continue beyond the field.

Creating or assigning an alternative interface name normally requires network administration privileges, but the triggering SIOCGARP caller does not need to be the actor that created it. This is an environmental prerequisite and not proof that the complete trigger requires host administration. No capability is required from a user or network namespace for SIOCGARP itself, so NamespaceScopedPrivilege is NO rather than YES.

There is no race. No special hardware is required. The bug is not directly reachable through incoming ARP traffic.

4. Primitive and severity interpretation

The exact primitive is a read past the end of arp_dev in a stack allocated struct arpreq. The read is caused by missing NUL termination before string based device lookup. This is CWE-170 and CWE-125.

The operation is read only. It does not modify adjacent stack data and does not establish memory corruption in the write sense. There is no UAF, repeated release, active stale object, shared backing modification or structured state corruption.

The demonstrated consequence is an internal kernel OOB read. A limited information oracle is plausible if lookup behavior can be correlated with adjacent stack bytes, but the supplied evidence does not show direct byte disclosure, a practical extraction method or sensitive data exposure. A production kernel crash is also not established.

PrimitiveClass is CLASS_C because the established behavior is an invalid read without an independently useful corruption or authorization primitive. ImportantCandidate is NO because there is no Important preserving primitive. AutoDowngradeAllowed is YES because manual analysis may confirm that the read has no practical disclosure channel.

The patch writes a terminating NUL to arp_dev at IFNAMSIZ minus one immediately after copy_from_user, ensuring that subsequent device name lookup cannot read beyond the field.

5. One-sentence report phrase

A locally supplied unterminated ARP device name can make alternative interface lookup read beyond a stack field, with a possible limited comparison oracle but no demonstrated write, crash or privilege escalation primitive.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review should determine whether device lookup results or timing provide a repeatable disclosure oracle for adjacent stack bytes. The established limited OOB read alone does not justify Important severity or mandatory preservation.

7. Call-site confidence

Call-site confidence: high

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

Patch: net: arp: terminate device name before lookup
Commit: ae6d704dbf9542b0a0830ec91a2db4f30307e7d8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae6d704dbf9542b0a0830ec91a2db4f30307e7d8

Commit description:

The ARP ioctl copies a user-provided struct arpreq into a stack object. Its
arp_dev field may contain IFNAMSIZ bytes without a NUL terminator.

Such input is passed to dev_get_by_name_rcu() or __dev_get_by_name(), where
strcmp() can read past the end of the stack object when a matching
alternative interface name exists.

Terminate the field before the lookup to prevent the out-of-bounds read.

Fixes: 36fbf1e ("net: rtnetlink: add linkprop commands to add and delete alternative ifnames")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Signed-off-by: Zijie Huang <milkory@outlook.com>
Signed-off-by: Ren Wei <weir@nebusec.ai>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/fabf02a70787d17299e4b3153eadffaf20d154b3.1789910973.git.milkory@outlook.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv4/arp.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=ae6d704dbf9542b0a0830ec91a2db4f30307e7d8

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

The original Linux kernel CVE announcement for CVE-2026-98495 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98495

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:H/PR:L/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS score: 3.3

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).