[CVE-2026-64018][IMPORTANT] net: mana: validate rx_req_idx to prevent out-of-bounds array access [ Upstream

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

CVE: CVE-2026-64018
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: net: mana: validate rx_req_idx to prevent out-of-bounds array access [ Upstream
Commit: 5ddc715324badd7f2641bc177db1d027b402adae
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5ddc715324badd7f2641bc177db1d027b402adae
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64018
Analysis date: Sun, 19 Jul 2026 22:06:03 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A device-controlled DMA value in the MANA HWC receive path can produce an out-of-bounds `reqs[]` index in the guest kernel, causing at least a guest DoS and potentially broader confidentiality or integrity impact across the Confidential VM device boundary.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64018 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64018

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: IMPORTANT
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-2026-64018	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-129;CWE-125;*CWE-20;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.8';DESCR 'mana_hwc_rx_event_handler derives rx_req_idx from sge address stored in DMA coherent memory and uses it to index the reqs array. In SEV-SNP/TDX Confidential VMs this shared memory can be modified by the virtual device or host side, so a malicious device endpoint can supply an out-of-range index and cause an out-of-bounds access in the guest kernel. For the CVSS the PR:N is used because no privileges are required inside the guest victim when the attacker controls or tampers with the adjacent virtual device interface. The issue is not directly Internet reachable and should be treated as adjacent to the VM or cloud device boundary rather than normal packet-triggered remote networking. Impact is at least denial of service via kernel crash and may include confidentiality or integrity impact because the bug creates a concrete out-of-bounds kernel memory access primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE OOB SIMPLEFIX ERRORPATH NETWORK KPANIC 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: **6**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Firmware-mediated external influence: +1**
  `rx_req_idx` is derived from DMA-coherent shared memory. In SEV-SNP/TDX Confidential VMs, the host or virtual device side can modify this memory.

* **Memory corruption, weak/indirect corruption candidate: +1**
  The bug is an unchecked index into `reqs[]`. The patch prevents an out-of-bounds array access, but the provided diff does not prove an arbitrary write or controlled overwrite primitive.

* **Reliable kernel crash / strong DoS: +1**
  An invalid `rx_req_idx` can select an invalid `rx_req`, after which `rx_req->buf_va` is dereferenced. A guest kernel crash is realistic.

* **Privileged kernel/device-management memory corruption path: +1**
  The affected code is in a trusted NIC driver receive-event path and processes DMA/device-provided metadata.

* **Confidentiality impact plausible: +1**
  Out-of-bounds object selection in kernel memory can plausibly expose or misuse adjacent kernel state, although no direct read-back leak is shown.

* **Integrity impact plausible: +1**
  Interpreting an out-of-bounds `reqs[]` entry as a valid request can corrupt driver or protocol state, even if a direct arbitrary write is not demonstrated.

Paranoid additional signal:

* **Cross-boundary isolation concern / weak privilege impact: +1**
  In the Confidential VM threat model, this is potentially a host or device-side influence over guest kernel memory safety, so it deserves Important-level manual scrutiny even without a proven full exploit chain.

No subtraction applied:

* No `CAP_*` requirement inside the guest victim is needed if the attacker controls or tampers with the adjacent virtual device interface.
* Not treated as public Internet remote reachability. This is adjacent/device-mediated, not ordinary network packet reachability.
* No rare-hardware penalty applied because MANA is a real cloud NIC path and the Confidential VM setting is central to the security model.

## 3. Reachability analysis

The realistic attacker is not a normal remote Internet host. The realistic attacker is a malicious or compromised host, hypervisor-side component, firmware/device endpoint, or virtual NIC side that can influence shared DMA-coherent memory visible to the guest.

Inside the guest, no local user privileges are required for the trigger if the attacker controls the device-side data path. This supports `PR:N` for the victim guest in a CVSS-style interpretation, but the attack vector is better modeled as adjacent/device-mediated rather than network-remote.

Namespaces and containers inside the guest do not materially change the main threat model, because the vulnerable input is not a container-local syscall or netlink operation. It is device-provided metadata consumed by the MANA driver.

Call-site confidence: **medium-high**. The patch shows the vulnerable index calculation and immediate use as `reqs[rx_req_idx]`, followed by dereferencing `rx_req->buf_va`. Deeper downstream consequences are not fully visible in the provided context.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is a concrete out-of-bounds kernel array access in a cloud NIC driver, with the index derived from device-controlled shared DMA state. It is not merely a validation cleanup or warning fix.

Conservatively, the demonstrated impact is a reliable guest kernel crash and device-path memory safety issue, making it an **Actionable Moderate** at minimum.

Paranoid interpretation reaches **Strong Important candidate** because the affected boundary is a Confidential VM guest kernel consuming host/device-modifiable shared memory. The patch does not prove arbitrary code execution, but the combination of OOB access, DMA-adjacent trust boundary, and possible guest-kernel compromise impact requires manual review.

## 5. One-sentence report phrase

A device-controlled DMA value in the MANA HWC receive path can produce an out-of-bounds `reqs[]` index in the guest kernel, causing at least a guest DoS and potentially broader confidentiality or integrity impact across the Confidential VM device boundary.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is a concrete OOB access in a DMA-adjacent cloud NIC path with a Confidential VM host/device-to-guest trust-boundary concern. It should not be auto-closed as a routine Moderate or driver-only crash.

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

Patch: net: mana: validate rx_req_idx to prevent out-of-bounds array access [ Upstream
Commit: 5ddc715324badd7f2641bc177db1d027b402adae
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5ddc715324badd7f2641bc177db1d027b402adae

Changed files:
  drivers/net/ethernet/microsoft/mana/hw_channel.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=5ddc715324badd7f2641bc177db1d027b402adae

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

The original Linux kernel CVE announcement for CVE-2026-64018 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64018

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.8

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: 6
  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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).