[CVE-2026-74701][MODERATE REGULAR] net/openvswitch: check Ethernet header length in key_extract() [ Upstream

[CVE-2026-74701][MODERATE REGULAR] net/openvswitch: check Ethernet header length in key_extract() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74701
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/openvswitch: check Ethernet header length in key_extract() [ Upstream
Commit: e85278afd4890dd190ba3c7a1b1a712b801c9fe1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e85278afd4890dd190ba3c7a1b1a712b801c9fe1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74701
Analysis date: Sat, 22 Aug 2026 17:43:38 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / Actionable Moderate candidate if delegated TUN or OVS access exists
Manual review required: YES

Summary:
Open vSwitch may crash the kernel when a short packet from an ARPHRD_NONE device such as TUN is classified as Ethernet without first verifying ETH_HLEN bytes are present.

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

The original Linux kernel CVE announcement for CVE-2026-74701 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74701

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-2026-74701	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-20;CWE-125;CWE-754;BEST CVSS score: '5.5';DESCR 'Open vSwitch can hit a kernel BUG in key_extract when a short packet arrives from an ARPHRD_NONE device such as TUN and skb protocol is set to ETH_P_TEB. The packet is treated as Ethernet even though the skb may not contain ETH_HLEN bytes of linear data, so MAC address extraction or ethertype parsing can reach __skb_pull with an invalid length and crash the kernel. For the CVSS the PR:L is used because reliable triggering requires a local user or process that can inject packets through a TUN or similar OVS attached device, not remote packet delivery alone. The issue is not directly network reachable from ordinary external traffic and depends on local access to the virtual network device or a delegated networking context. Impact is denial of service via kernel crash. No concrete UAF, OOB write, information leak, or privilege escalation primitive is supported by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate candidate if delegated TUN or OVS access exists (with actual score 4)	YES	DANGER SIMPLEFIX SKB HARDWARE PACKET  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / Actionable Moderate candidate if delegated TUN or OVS access exists**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1
  The patch and trace show a kernel BUG in `__skb_pull()` reachable from `key_extract()` when an Ethernet header is assumed but not present.

* Availability impact realistic: +1
  The failure is a host kernel BUG, not just packet drop or warning. Once the vulnerable path is reachable, the impact is a real kernel crash.

* Common packet-processing / virtual networking path: +1
  The bug is in Open vSwitch packet key extraction and can be reached through a TUN backed virtual networking path.

Paranoid additional signal:

* Local unprivileged trigger: +1
  This applies only if a low-privileged local user, container workload, VM process, or delegated networking service can inject packets into an already configured TUN or OVS-attached device.

Not awarded:

* Remote reachable / network-triggerable: +0
  Ordinary external packets do not directly reach this path. The trigger depends on local or delegated virtual device injection.

* Generic memory corruption: +0
  The demonstrated primitive is a short-header validation failure causing `BUG` in `__skb_pull()`, not UAF, OOB write, double free, type confusion, or controlled overwrite.

* Privilege escalation plausible: +0
  No reclaim, write primitive, object confusion, callback control, or refcount takeover is supported by the patch context.

## 3. Reachability analysis

The bug can be triggered by a local actor able to inject a crafted short packet through an `ARPHRD_NONE` device such as TUN when that device is connected into the Open vSwitch receive path and `skb->protocol` is set to `ETH_P_TEB`.

Creating or attaching such devices commonly requires `CAP_NET_ADMIN` or administrator controlled OVS configuration. However, in virtualized or containerized deployments, a TUN file descriptor or virtual network endpoint may be delegated to a less privileged workload, making the paranoid PR:L style interpretation reasonable.

The path is not directly Internet reachable. Exposure is mainly on hosts using OVS with TUN or similar virtual ports where untrusted or semi-trusted workloads can inject frames.

Call-site confidence: high. The commit message includes the concrete call chain through `tun_get_user()`, `netdev_frame_hook()`, `ovs_vport_receive()`, and `ovs_flow_key_extract()`.

## 4. Severity interpretation

This behaves like an actionable local DoS issue, not an Important-class memory corruption vulnerability. The realistic impact is a kernel crash through missing Ethernet header length validation. The theoretical risk does not extend to privilege escalation based on the supplied patch because the failure path is a bounds check leading to `BUG`, with no supported UAF, OOB write, stale pointer reuse, or attacker-controlled corruption primitive.

The issue should not be treated as a generic remote networking vulnerability, but it also should not be blindly auto-closed where OVS/TUN access is delegated to tenants or containers.

## 5. One-sentence report phrase

Open vSwitch may crash the kernel when a short packet from an ARPHRD_NONE device such as TUN is classified as Ethernet without first verifying ETH_HLEN bytes are present.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because practical severity depends heavily on deployment: systems with OVS plus delegated TUN or container networking access may expose this as a low-privilege host DoS, while systems requiring full admin control over the OVS/TUN path are lower priority.

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

Patch: net/openvswitch: check Ethernet header length in key_extract() [ Upstream
Commit: e85278afd4890dd190ba3c7a1b1a712b801c9fe1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e85278afd4890dd190ba3c7a1b1a712b801c9fe1

Changed files:
  include/linux/skbuff.h
  net/openvswitch/flow.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=e85278afd4890dd190ba3c7a1b1a712b801c9fe1

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

The original Linux kernel CVE announcement for CVE-2026-74701 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74701

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 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).