[CVE-2026-68425][MODERATE REGULAR] IB/mad: Drop unmatched RMPP responses before reassembly [ Upstream

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

CVE: CVE-2026-68425
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: IB/mad: Drop unmatched RMPP responses before reassembly [ Upstream
Commit: dfa535c94406c03d3f0c869ef3ba5528e395737c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dfa535c94406c03d3f0c869ef3ba5528e395737c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68425
Analysis date: Mon, 10 Aug 2026 12:37:01 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / Actionable Moderate at minimum
Manual review required: YES

Summary:
Kernel handled IB MAD RMPP DATA responses could enter reassembly before matching an outstanding send, allowing an attacker with access to the RDMA or InfiniBand fabric to create or extend unmatched receive state and potentially cause denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-68425 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68425

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-2026-68425	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-20;**CWE-400;CWE-770;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'Kernel handled IB MAD RMPP DATA responses could enter receive side reassembly before being matched to an outstanding send request. An unsolicited response that reaches a kernel RMPP agent by high TID bits may allocate or extend RMPP receive state before the full TID, management class, and source address are validated. For the CVSS the PR:N is used because the attacker does not need a local account or code execution on the victim, but must be able to send MAD RMPP traffic on the relevant InfiniBand or RDMA fabric. The issue is not Internet remote in the usual sense and is better modeled as AV:A because exploitation requires access to the local fabric or storage cluster network. Impact is primarily denial of service through receive state or memory pressure. No concrete UAF, OOB access, information leak, or write primitive is evident from the patch, so confidentiality and integrity are not raised for this assessment.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate at minimum (with actual score 4)	YES	OOB LOCK DANGER INIT NETWORK LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  The affected path processes incoming IB MAD RMPP responses from the RDMA or InfiniBand fabric. This is not Internet remote, but it is externally triggerable from the relevant local fabric.

* Availability impact realistic: +1
  Unmatched RMPP DATA responses can allocate or extend receive-side reassembly state before full request matching. This supports a realistic resource/state exhaustion DoS concern.

Paranoid additional signal:

* Reliable kernel crash / strong DoS: +1
  Not directly shown as a panic or UAF, but sustained unsolicited RMPP traffic could plausibly create enough kernel receive state pressure to cause stronger availability impact.

Signals not applied:

* Generic memory corruption: +0
  The patch does not show UAF, OOB access, double free, type confusion, arbitrary write, or stale callback use.

* Privilege escalation plausible: +0
  No reclaim, overwrite, refcount takeover, callback dispatch, or controlled object confusion is evident.

* Confidentiality / integrity impact: +0
  The described primitive is pre-validation state allocation or extension, not data disclosure or modification.

* Rare subsystem penalty: 0
  RDMA/InfiniBand is deployment-specific, but the path is a normal fabric-facing kernel receive path when the subsystem is in use. I would not subtract heavily for rarity.

## 3. Reachability analysis

An attacker would need the ability to send crafted MAD/RMPP traffic on the relevant InfiniBand or RDMA management fabric. No local account on the victim is required, so practical CVSS-style PR is PR:N, but the attack is better modeled as adjacent/fabric-reachable rather than Internet-reachable.

Namespaces and containers are not the main access boundary here. The meaningful boundary is access to the RDMA/IB fabric and whether kernel-handled RMPP agents are active. This is not a default Internet-exposed path, but it can matter in storage, HPC, and clustered environments.

## 4. Severity interpretation

This behaves like an actionable Moderate network-adjacent DoS candidate, not an Important-class memory corruption issue based on the provided patch. The strongest demonstrated issue is that unmatched responses can consume kernel RMPP receive state before full validation.

Theoretical impact beyond DoS is not supported by the diff. There is no concrete UAF, overwrite, stale object reuse, information leak, or privilege escalation primitive. Manual review is still recommended because the bug is externally reachable from a fabric network and affects kernel-side receive state before validation.

## 5. One-sentence report phrase

Kernel handled IB MAD RMPP DATA responses could enter reassembly before matching an outstanding send, allowing an attacker with access to the RDMA or InfiniBand fabric to create or extend unmatched receive state and potentially cause denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: network-adjacent kernel receive-state allocation before validation is security-relevant and should not be auto-closed, but the patch does not currently justify Important severity or memory-corruption impact.

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

Patch: IB/mad: Drop unmatched RMPP responses before reassembly [ Upstream
Commit: dfa535c94406c03d3f0c869ef3ba5528e395737c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dfa535c94406c03d3f0c869ef3ba5528e395737c

Changed files:
  drivers/infiniband/core/mad.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=dfa535c94406c03d3f0c869ef3ba5528e395737c

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

The original Linux kernel CVE announcement for CVE-2026-68425 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68425

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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 3
  Paranoid ActionableScore: 4

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).