[CVE-2026-74475][MODERATE 7.0] vxlan: use neigh_ha_snapshot() in route_shortcircuit()

[CVE-2026-74475][MODERATE 7.0] vxlan: use neigh_ha_snapshot() in route_shortcircuit()

[AL-KERNEL]

CVE: CVE-2026-74475
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: vxlan: use neigh_ha_snapshot() in route_shortcircuit()
Commit: d08e8ac13f2e228cc7fc3c70b5ebe71557b624a0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d08e8ac13f2e228cc7fc3c70b5ebe71557b624a0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74475
Analysis date: Sat, 15 Aug 2026 13:30:42 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
A race in VXLAN route_shortcircuit() can read a partially updated neighbour MAC address and use it for Ethernet header rewriting, potentially causing network-adjacent packet misdelivery or forwarding disruption without evidence of kernel memory corruption.

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

The original Linux kernel CVE announcement for CVE-2026-74475 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74475

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: NO

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-2026-74475	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-362;CWE-667;CWE-362;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L';BEST CVSS score: '6.4';DESCR 'VXLAN route_shortcircuit reads the neighbour hardware address while it may be updated asynchronously by the neighbour subsystem, which can produce a torn or partially updated MAC address. The mixed MAC value can then be used when comparing and rewriting the Ethernet destination address, causing packet misdelivery, transient traffic blackholing, or weaker forwarding integrity. For the CVSS the PR:N is used because an adjacent network attacker may not need local code execution if they can influence neighbour resolution while VXLAN route_shortcircuit is active. The issue is network adjacent rather than generally Internet reachable, and exploitation depends on timing a race during neighbour hardware address updates. Impact is mainly forwarding disruption and possible limited confidentiality or integrity impact for affected traffic, not kernel memory corruption or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	OOB SIMPLEFIX NETWORK SKB HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  The affected code is in the VXLAN packet forwarding path, and the bad value can be influenced through neighbour address changes in a network-adjacent scenario.
* Confidentiality impact plausible: +1
  A torn MAC address can theoretically cause limited packet misdelivery to an unintended L2 destination.
* Integrity impact plausible: +1
  The Ethernet destination address can be rewritten using a partially updated neighbour address, weakening forwarding correctness.
* Availability impact realistic: +1
  The issue can cause packet blackholing or forwarding disruption.
* Hard or unreliable race / special timing required: -1
  Exploitation depends on racing route_shortcircuit() against asynchronous neighbour hardware address updates.

Paranoid additional signal:

* Common networking packet-processing path: +1
  VXLAN is a common overlay networking mechanism in virtualized and containerized environments, even though it is not universally enabled by default.

No memory corruption signal is awarded. The patch shows a torn read of a MAC address, not UAF, OOB access, double free, type confusion, arbitrary write, or refcount misuse.

## 3. Reachability analysis

The most realistic attacker is network-adjacent to the affected VXLAN or underlay neighbour-resolution domain and able to influence neighbour entry churn while VXLAN route_shortcircuit() processes packets. No local code execution on the victim is necessarily required in the paranoid network-adjacent model, so PR:N is defensible for CVSS-style reasoning. The path is not generally Internet-reachable and requires VXLAN plus route short-circuit behaviour and neighbour updates, so timing and deployment conditions matter. Containers or namespaces may matter if an untrusted tenant can influence VXLAN traffic or neighbour resolution, but ordinary local privilege escalation is not indicated.

Call-site confidence: high. The provided diff includes the direct read and later use of n->ha in route_shortcircuit().

## 4. Severity interpretation

This behaves more like an actionable Moderate networking race than an Important-class memory corruption issue. The theoretical impact is packet misdelivery, limited confidentiality or integrity impact for affected traffic, and forwarding disruption. Realistic exploitation evidence for privilege escalation or kernel memory corruption is absent. Manual review is still reasonable because the bug is in a network packet-processing path and the commit explicitly notes similar issues may remain in arp_reduce() and neigh_reduce().

## 5. One-sentence report phrase

A race in VXLAN route_shortcircuit() can read a partially updated neighbour MAC address and use it for Ethernet header rewriting, potentially causing network-adjacent packet misdelivery or forwarding disruption without evidence of kernel memory corruption.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the issue is network-adjacent and affects packet forwarding correctness, but the patch supports only torn-read based misdelivery or DoS impact, not a concrete memory corruption or privilege escalation primitive.

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

Patch: vxlan: use neigh_ha_snapshot() in route_shortcircuit()
Commit: d08e8ac13f2e228cc7fc3c70b5ebe71557b624a0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d08e8ac13f2e228cc7fc3c70b5ebe71557b624a0

Commit description:

The neighbour hardware address n->ha can be updated asynchronously by the
neighbour subsystem, protected by n->ha_lock seqlock. Reading n->ha without
holding the seqlock loop can lead to torn reads or reading a partially updated
MAC address.

Use neigh_ha_snapshot() in route_shortcircuit() to safely copy n->ha under
read_seqbegin()/read_seqretry() lock protection before using it.

Note that arp_reduce() and neigh_reduce() seem to have the same issue
left for future patches.

Fixes: e4f67ad ("add DOVE extensions for VXLAN")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://patch.msgid.link/20260723144249.759100-4-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/vxlan/vxlan_core.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=d08e8ac13f2e228cc7fc3c70b5ebe71557b624a0

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

The original Linux kernel CVE announcement for CVE-2026-74475 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74475

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:H/PR:N/UI:N/S:U/C:L/I:L/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.4

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: 5

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 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).