[CVE-2026-93830][MODERATE REGULAR] net: stmmac: xgmac2: disable RBUE in default RX interrupt mask [ Upstream

[CVE-2026-93830][MODERATE REGULAR] net: stmmac: xgmac2: disable RBUE in default RX interrupt mask [ Upstream

[AL-KERNEL]

CVE: CVE-2026-93830
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: stmmac: xgmac2: disable RBUE in default RX interrupt mask [ Upstream
Commit: 0b1a5d3647ce07c27a9fffefc11a8cbf7d7b25ce
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b1a5d3647ce07c27a9fffefc11a8cbf7d7b25ce
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93830
Analysis date: Thu, 24 Sep 2026 20:04:01 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-93830 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93830

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-2026-93830	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-93830 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-400;CWE-770;CWE-799;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'An interrupt storm can occur in the stmmac XGMAC2 receive path because the RX Buffer Unavailable interrupt remains asserted while the DMA has no available RX descriptors. The RBUE handler provides no additional recovery beyond the normal RX completion path and repeated interrupts can consume substantial CPU time without making progress when page_pool allocation or ring refill fails. A remote attacker may trigger or amplify the condition by sending sustained high rate traffic to an affected network interface, although reliable triggering depends on XGMAC2 hardware and sufficient RX pressure. For the CVSS the PR:N value is used because no authenticated local user or privileged execution context is required when the condition is triggered only by incoming network traffic. Impact is denial of service through CPU exhaustion, reduced system responsiveness, or loss of network receive service. No UAF, OOB access, information disclosure, or write primitive is supported by the available code change, so confidentiality and integrity remain unaffected.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)  SKIP CVE-2026-93830 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	REMOTE NETWORK DMAorINTERRUPT HARDWARE LINUS  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Positive signals:

* +2 Remote reachable. Incoming high-rate traffic can exhaust the RX descriptor ring and cause RBUE interrupts without requiring local execution or authentication.
* +1 Strong DoS. The observed interrupt amplification was approximately 695 times the number of RX completions and can consume substantial CPU time without forward progress.

Negative signals:

* No negative points. XGMAC2 hardware is required, but the evidence does not establish that it is sufficiently rare or physically attacker-controlled to justify a hardware penalty.
* No race penalty. This is a sustained load condition rather than a narrow or uncontrollable timing race.

Important non-awarded signals:

* No corruption bonus. The patch establishes an interrupt storm and resource exhaustion, not memory corruption.
* No UAF, OOB access, stale object, overwrite, information disclosure, or authorization bypass is established.
* No additional Availability point. CPU and network unavailability are consequences of the same interrupt storm.
* No common networking core bonus. The vulnerable operation is specific to the stmmac XGMAC2 driver rather than a general TCP/IP or common skb path.
* No Important-grade resource-exhaustion signal. There is no cgroup bypass, cross-container accounting bypass, persistent leak, or lasting failure after recovery.
* The paranoid score is not increased because no stronger technically defensible primitive exists beyond the same DoS behavior.

3. Reachability analysis

An external sender whose traffic reaches an affected XGMAC2 interface can contribute to RX descriptor exhaustion through sustained high-rate traffic. No local user context, authentication, capability, or host-administrator operation is required for packet reception, so HostAdminRequired is NO.

The system must contain an XGMAC2 device using the affected default interrupt mask and the interface must be active and reachable. This is an environmental hardware prerequisite, not an attacker-performed privileged setup step. The evidence does not establish that user or network namespaces are relevant to the complete trigger, so NamespaceScopedPrivilege is UNKNOWN.

The trigger is repeatable under heavy RX pressure and is not a race. Practical reliability depends on traffic rate, ring refill behavior, page_pool pressure, CPU capacity, and whether the attacker can deliver enough traffic to the affected interface. The demonstrated impact may range from loss of RX service to significant CPU starvation. A kernel panic or persistent host-wide failure is not established.

4. Primitive and severity interpretation

The exact primitive is uncontrolled interrupt amplification after the DMA runs out of RX descriptors. RBUE remains active while the handler merely requests the same RX processing already provided by RIE. If page_pool allocation fails, ring refill cannot advance the DMA tail and repeated interrupts occur without recovery progress.

This is CLASS_C because the demonstrated behavior is resource exhaustion and denial of service without an independently useful corruption or lifetime primitive. It is neither an active structured UAF nor fixed stale storage. No repeated release or refcount mutation exists.

The demonstrated consequence is excessive CPU consumption and possible network receive failure. Host-wide denial of service is plausible under severe interrupt pressure, but memory corruption, confidentiality impact, integrity impact, privilege escalation, and persistent compromise are unsupported.

ImportantCandidate is NO because the issue lacks corruption, ownership violation, authorization bypass, persistent cross-boundary exhaustion, or another Important-preserving primitive. AutoDowngradeAllowed is YES because no unresolved exploitation leverage would be discarded by treating it as an operational DoS issue. Manual review remains recommended because the trigger is potentially remote and deployment-specific testing is needed to determine whether the storm affects only the interface or broader host availability.

5. One-sentence report phrase

A remote high-rate traffic source may cause an RBUE interrupt storm on affected XGMAC2 interfaces when RX descriptors cannot be refilled, resulting in CPU exhaustion or loss of network receive service without evidence of memory corruption.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether attacker-controlled traffic can reliably produce the required RX pressure on deployed XGMAC2 hardware and whether the resulting interrupt storm causes interface-local degradation or host-wide denial of service.

7. Call-site confidence

Call-site confidence: medium

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

Patch: net: stmmac: xgmac2: disable RBUE in default RX interrupt mask [ Upstream
Commit: 0b1a5d3647ce07c27a9fffefc11a8cbf7d7b25ce
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b1a5d3647ce07c27a9fffefc11a8cbf7d7b25ce

Changed files:
  drivers/net/ethernet/stmicro/stmmac/dwxgmac2.h

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=0b1a5d3647ce07c27a9fffefc11a8cbf7d7b25ce

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

The original Linux kernel CVE announcement for CVE-2026-93830 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93830

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:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 7.5

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: 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).