[CVE-2026-63987][MODERATE 7.0] ethtool: coalesce: cap profile updates at NET_DIM_PARAMS_NUM_PROFILES [ Upstream

[CVE-2026-63987][MODERATE 7.0] ethtool: coalesce: cap profile updates at NET_DIM_PARAMS_NUM_PROFILES [ Upstream

[AL-KERNEL]

CVE: CVE-2026-63987
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ethtool: coalesce: cap profile updates at NET_DIM_PARAMS_NUM_PROFILES [ Upstream
Commit: d4c9cc7c47781c6f4fa29d80a1193a8bcd1525bc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d4c9cc7c47781c6f4fa29d80a1193a8bcd1525bc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63987
Analysis date: Sun, 19 Jul 2026 16:54:19 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local actor with ethtool coalesce profile update privileges can submit more `ETHTOOL_A_PROFILE_IRQ_MODERATION` nested attributes than the fixed `NET_DIM_PARAMS_NUM_PROFILES` array holds, causing a heap out-of-bounds write that may lead to kernel crash and should be reviewed for possible privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-63987 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63987

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 7.0
Manual review required: YES

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

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-63987	MODERATE	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:H/I:H/A:H';*CWE-787;CWE-122;*CWE-20;CWE-129;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'ethnl_update_profile processes a user controlled Netlink nest list and writes entries into a fixed size profile array without checking that the index stays below NET_DIM_PARAMS_NUM_PROFILES. A local actor who can issue the relevant ethtool coalesce profile update can provide more nested ETHTOOL_A_PROFILE_IRQ_MODERATION entries than the destination array holds, causing a heap out-of-bounds write. For the CVSS the PR:L is used for the paranoid score because reliable triggering requires network administration capability such as CAP_NET_ADMIN, but this capability can be delegated to a container root, network namespace administrator, or service account without full host root. The issue is not directly network reachable through packet traffic and is triggered through the local Netlink control plane. Impact is at least local denial of service via kernel memory corruption and in worst case may allow confidentiality or integrity impact including privilege escalation, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	SIMPLEFIX LINUS  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	YES	NO	checked

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

ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, strong corruption primitive: +2. The patch fixes an unchecked write to `new_profile[i++]` where `new_profile` has only `NET_DIM_PARAMS_NUM_PROFILES` entries.
* Reliable kernel crash / strong DoS: +1. A heap out-of-bounds write in this path can realistically crash the kernel.
* Privileged kernel/device-management memory corruption path: +1. The bug is in ethtool Netlink control-plane handling for network device coalesce profile configuration.
* Requires CAP_NET_ADMIN in typical deployments: -2. Normal triggering requires permission to change ethtool settings for a network device.
* Corruption target not fully attacker-selected: -1. The attacker controls the number of nested entries and likely profile values, but not the adjacent heap object selected as overwrite target.
* Broad/common networking administration interface: +1. ethtool Netlink is a common kernel network device management interface.

Paranoid additional interpretation:

* Privilege escalation plausible: +2. A heap OOB write with user-controlled Netlink input can plausibly exceed DoS, especially if profile fields influence overwritten heap bytes.
* Confidentiality impact plausible: +1. If heap corruption is exploitable, disclosure or privilege boundary impact cannot be excluded.
* Integrity impact plausible: +1. Heap corruption may allow modification of kernel state beyond the profile object.
* Reduced privilege model instead of full host root: penalty relaxed from -2 to -1. CAP_NET_ADMIN may be delegated to container root, network namespace administrators, or service accounts without full host-root equivalence.

## 3. Reachability analysis

The bug is locally reachable through the ethtool Netlink control plane, not through ordinary packet traffic. A typical attacker needs CAP_NET_ADMIN or an equivalent ability to modify network device coalesce profile settings. In containerized or delegated network namespace environments, this may be meaningfully less than full host-root authority, so the paranoid score uses a lower privilege interpretation. The affected path is not remote-network-triggerable by packets, but ethtool Netlink and network device management are common enough that this should not be treated as a rare subsystem issue.

Call-site confidence: medium. The provided patch shows the vulnerable write and the fixed bound check directly, but not the full allocation and commit path around `kmemdup()`.

## 4. Severity interpretation

This is not an ordinary Moderate resource or validation issue. The concrete primitive is a user-controlled over-count causing writes past a fixed-size heap allocation. Realistic exploitation may be limited by CAP_NET_ADMIN requirements and by imperfect control over the adjacent heap target, so the conservative score remains borderline. However, because the primitive is a heap OOB write in a kernel Netlink control path and delegated CAP_NET_ADMIN is common in practical deployments, the paranoid score reaches Strong Important candidate territory.

## 5. One-sentence report phrase

A local actor with ethtool coalesce profile update privileges can submit more `ETHTOOL_A_PROFILE_IRQ_MODERATION` nested attributes than the fixed `NET_DIM_PARAMS_NUM_PROFILES` array holds, causing a heap out-of-bounds write that may lead to kernel crash and should be reviewed for possible privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch fixes a concrete heap out-of-bounds write from user-controlled Netlink input, and CAP_NET_ADMIN delegation can make the trigger reachable by less-than-full-root actors in container or namespace-based deployments.

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

Patch: ethtool: coalesce: cap profile updates at NET_DIM_PARAMS_NUM_PROFILES [ Upstream
Commit: d4c9cc7c47781c6f4fa29d80a1193a8bcd1525bc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d4c9cc7c47781c6f4fa29d80a1193a8bcd1525bc

Changed files:
  net/ethtool/coalesce.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=d4c9cc7c47781c6f4fa29d80a1193a8bcd1525bc

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

The original Linux kernel CVE announcement for CVE-2026-63987 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63987

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 4
  Paranoid ActionableScore: 7

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).