[CVE-2026-74744][IMPORTANT] ipvlan: inherit needed_headroom and needed_tailroom from phy_dev [ Upstream

[CVE-2026-74744][IMPORTANT] ipvlan: inherit needed_headroom and needed_tailroom from phy_dev [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74744
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: ipvlan: inherit needed_headroom and needed_tailroom from phy_dev [ Upstream
Commit: af602c4d0ee548da18e2409b4b4da1079625a372
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af602c4d0ee548da18e2409b4b4da1079625a372
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74744
Analysis date: Wed, 26 Aug 2026 14:03:02 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
ipvlan devices failed to inherit lower-device headroom and tailroom requirements, allowing traffic through certain stacked network configurations to trigger skb underflow or KASAN slab-use-after-free crashes, with local DoS confirmed and memory-corruption impact requiring manual review.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74744 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74744

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-2026-74744	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-787;CWE-119;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'ipvlan devices did not inherit needed_headroom and needed_tailroom from the underlying physical or stacked lower device. When the lower path needs extra space for headers or trailers, upper layers may allocate skb buffers with insufficient reserve, and later header prepend or trailer append operations can hit skb headroom underflow or KASAN slab use after free conditions. For the CVSS the PR:L is used because reliable triggering generally requires a local process or tenant workload able to send traffic through an already configured ipvlan device, while creating the ipvlan and lower stack usually requires administrator setup. The issue is not treated as directly Internet reachable, although traffic through the affected ipvlan path can be network influenced in container or virtual networking deployments. Impact is at least local denial of service via kernel crash, and in the paranoid case may include confidentiality or integrity impact because the bug class includes skb memory corruption and a reported slab use after free.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8)	YES	OOB DANGER UAF NETWORK SKB KERNEL_PANIC_PLUS_UAF HARDWARE SYZBOT KPANIC PACKET 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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## 1. ActionableScore

ActionableScore=8
ActionableScoreLower=6

* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local workload can plausibly trigger traffic through an already configured ipvlan device.
* Generic memory corruption: +2. The description explicitly mentions skb headroom underflows and KASAN slab-use-after-free crashes.
* Memory layout invariant restoration: +1. The patch restores consistency between lower-device headroom/tailroom requirements and upper ipvlan skb allocation assumptions.
* Real lifetime corruption: +1. Reported KASAN slab-use-after-free indicates a real lifetime or stale memory access condition, not just bookkeeping.
* Reliable kernel crash / strong DoS: +1. The commit describes KASAN crashes in packet header or trailer handling paths.
* Common networking packet-processing path: +1. ipvlan is not universal, but this is still an skb transmit/stacked-netdev packet path.
* Special configuration required: -1. Reliable triggering depends on ipvlan over a lower device needing extra headroom or tailroom, such as macsec, IPsec, WireGuard, tunnels, or veth rx headroom.

Paranoid additional signals:

* Weak LPE concern: +1. The UAF/headroom-underflow class is security-relevant, but no attacker-controlled reclaim, callback control, or arbitrary write primitive is shown.
* Integrity impact plausible: +1. skb memory corruption can plausibly affect kernel/network state beyond a clean crash, so this deserves manual review.

Not counted:

* Remote reachable: +0. This is network-influenced, but not directly Internet-reachable in the normal CVE sense.
* Strong LPE plausibility: +0. No demonstrated reclaim, object replacement, type confusion, or controlled overwrite is shown.
* Confidentiality impact: +0 for ActionableScore. It remains a paranoid CVSS consideration, but no concrete leak path is shown.

## 3. Reachability analysis

The most realistic trigger is a local process, container workload, or tenant workload sending packets through an already configured ipvlan interface whose lower device requires nonzero needed_headroom or needed_tailroom. Creating the ipvlan and lower stacked configuration usually requires CAP_NET_ADMIN, but once the device exists, ordinary traffic generation may be enough to exercise the vulnerable path. Namespaces and container networking can therefore reduce practical privilege requirements if ipvlan devices are delegated to containers or tenant workloads. The path is not default-enabled on all systems, but ipvlan and stacked virtual or encrypted network devices are common enough that this should not be treated as obscure hardware-only exposure.

Call-site confidence: medium-high. The patch is small, but the commit message identifies concrete downstream users, dev_hard_header(), ipvlan_hard_header(), and lower-device tailroom append paths.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because the failure mode is not just validation failure or resource exhaustion. The bug affects skb buffer sizing invariants and has reported KASAN slab-use-after-free crashes. Realistic evidence supports local DoS with special network configuration. Theoretical impact may extend to integrity or privilege escalation, but the patch does not show a controlled corruption primitive. Therefore the conservative result is Actionable Moderate, while the paranoid result is a Strong Important candidate requiring manual review.

## 5. One-sentence report phrase

ipvlan devices failed to inherit lower-device headroom and tailroom requirements, allowing traffic through certain stacked network configurations to trigger skb underflow or KASAN slab-use-after-free crashes, with local DoS confirmed and memory-corruption impact requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is skb memory corruption with a reported KASAN slab-use-after-free in a network packet path. Even though practical exploitation likely requires a specific ipvlan/lower-device configuration and no strong LPE primitive is demonstrated, the bug class is too security-relevant to auto-close.

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

Patch: ipvlan: inherit needed_headroom and needed_tailroom from phy_dev [ Upstream
Commit: af602c4d0ee548da18e2409b4b4da1079625a372
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af602c4d0ee548da18e2409b4b4da1079625a372

Changed files:
  drivers/net/ipvlan/ipvlan_main.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=af602c4d0ee548da18e2409b4b4da1079625a372

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

The original Linux kernel CVE announcement for CVE-2026-74744 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74744

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:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 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: 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).