[CVE-2026-43208][MODERATE 7.0] net: do not pass flow_id to set_rps_cpu() [ Upstream

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

CVE: CVE-2026-43208
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net: do not pass flow_id to set_rps_cpu() [ Upstream
Commit: 5455a232edea6b946b99449f15ca771a8874a5a6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5455a232edea6b946b99449f15ca771a8874a5a6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43208
Analysis date: Wed, 20 May 2026 17:36:26 -0400
ActionableScore: 8
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
A stale RPS/RFS `flow_id` can be reused against a different receive-queue flow table, allowing network-triggered out-of-bounds access and potential kernel crash or metadata corruption when RPS/RFS is configured.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-43208 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43208

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-2026-43208	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-125;CWE-129;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'The RPS/RFS receive path could reuse a flow_id computed for one receive queue flow table when updating another queue flow table in set_rps_cpu. If per queue flow tables have different sizes or change over time, the stale flow_id can index outside the target flow table and corrupt or read adjacent kernel metadata. For the CVSS the PR:N is used for the paranoid network interpretation because a remote sender does not need local credentials when packet traffic can reach an interface with RPS/RFS enabled and configured. The issue is network reachable only under those configuration preconditions, so AC:H is used. Impact is at least denial of service via out of bounds access or crash, and worst case may include confidentiality and integrity impact because the affected path can perform writes to rps_dev_flow metadata. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 6.5)	MAYBE	REMOTE OOB DANGER SIMPLEFIX SKB KERNEL_PANIC_PLUS_UAF HARDWARE KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate**

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. The bug is in the packet receive path and can be exercised by traffic reaching an interface with RPS/RFS configured.
* Memory corruption, weak or indirect corruption candidate: +1. A `flow_id` computed for one RPS flow table can be reused against another table, causing an out-of-bounds flow table access.
* Reliable kernel crash / strong DoS: +1. The commit explicitly mentions out-of-bound access and/or crashes.
* Availability impact realistic: +1. A kernel crash in the network receive path is system-wide DoS.
* Common networking core path: +1. The affected code is in `net/core/dev.c` receive steering logic.
* Rare or configuration-dependent exposure: -1. Practical triggering requires RPS/RFS flow tables and a mismatch or change in per-queue table sizes.
* Constrained metadata-only primitive: -1. The corrupted or accessed object is RPS/RFS flow metadata, and attacker-controlled payload or target control is not demonstrated.

Paranoid signals:

* Memory corruption, stronger OOB candidate: +2 instead of +1. The stale index may reach outside the target `flow_table->flows` array and the surrounding code can operate on `rps_dev_flow` metadata.
* Weak LPE concern: +1. Kernel networking metadata corruption in a packet receive path can be security relevant, but no arbitrary write or reliable object confusion primitive is shown.
* Confidentiality impact plausible: +1. Out-of-bounds access could theoretically expose or influence adjacent metadata, though no direct disclosure path is shown.
* Integrity impact plausible: +1. If the OOB access reaches writable metadata, limited integrity impact is plausible.
* The same configuration and constrained-primitive deductions still apply.

## 3. Reachability analysis

A remote sender may influence the vulnerable path by sending traffic to a network interface where RPS/RFS receive steering is enabled and configured. No local credentials are needed for the packet source in that interpretation, but the system must have the relevant RPS/RFS tables configured and the vulnerable cross-table `flow_id` reuse condition must occur. Containers do not materially lower the remote requirement, but local privileged network configuration controls whether RPS/RFS exposure exists. This is not a universal default Internet-facing condition, but it is a realistic networking-core receive-path scenario on tuned systems.

## 4. Severity interpretation

Conservatively this is an actionable Moderate because the demonstrated impact is OOB access and crash under configuration-specific RPS/RFS conditions. Paranoid scoring reaches Strong Important candidate because the bug is network-triggerable in a common kernel networking path and may involve OOB access to writable kernel metadata. Theoretical memory corruption potential exists, but practical privilege escalation is not demonstrated by the patch.

## 5. One-sentence report phrase

A stale RPS/RFS `flow_id` can be reused against a different receive-queue flow table, allowing network-triggered out-of-bounds access and potential kernel crash or metadata corruption when RPS/RFS is configured.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: network-reachable OOB access in `net/core/dev.c` receive steering is a high-sensitivity pattern, even though exploitation depends on RPS/RFS configuration and the corruption primitive appears constrained.

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

Patch: net: do not pass flow_id to set_rps_cpu() [ Upstream
Commit: 5455a232edea6b946b99449f15ca771a8874a5a6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5455a232edea6b946b99449f15ca771a8874a5a6

Changed files:
  net/core/dev.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=5455a232edea6b946b99449f15ca771a8874a5a6

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

The original Linux kernel CVE announcement for CVE-2026-43208 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43208

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 5
  Paranoid ActionableScore: 8

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).