[CVE-2026-74474][MODERATE 7.0] vxlan: use pskb_network_may_pull() for transmit path header pulls

[CVE-2026-74474][MODERATE 7.0] vxlan: use pskb_network_may_pull() for transmit path header pulls

[AL-KERNEL]

CVE: CVE-2026-74474
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: vxlan: use pskb_network_may_pull() for transmit path header pulls
Commit: 94dee751aad627b3645d424b5d0c736d394573e9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=94dee751aad627b3645d424b5d0c736d394573e9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74474
Analysis date: Sat, 15 Aug 2026 19:01:52 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
VXLAN transmit processing used `pskb_may_pull()` without accounting for the MAC-to-network-header offset, allowing specially shaped non-linear skb traffic to leave network headers partially non-linear and potentially trigger invalid header reads or kernel crash in affected VXLAN proxy or MDB paths.

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

The original Linux kernel CVE announcement for CVE-2026-74474 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74474

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-2026-74474	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-125;*CWE-20;CWE-754;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'VXLAN transmit path code used pskb_may_pull() to validate ARP, IPv6/ND, and IP/IPv6 MDB headers even though skb data still points at the MAC header on this path. This can leave part of the network header in non-linear skb fragments while later code reads arp_hdr(), ipv6_hdr(), or ip_hdr() as if the header were fully linear. A reachable attacker may be able to trigger an invalid header read or crash by causing specially shaped traffic to be transmitted through a VXLAN device with affected proxy or MDB handling enabled. For the CVSS the PR:N value is used for the paranoid score because a network adjacent sender may not need an account on the target when traffic can enter a bridge or overlay path that transmits through VXLAN. The issue is not a general Internet remote bug in typical deployments because VXLAN is usually used inside data center, tenant, or trusted overlay networks. Impact is at least denial of service via packet processing failure or kernel crash, with limited confidentiality or integrity impact kept only as a manual review sensitive worst case due to invalid reads from skb linear data.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 7)	YES	SIMPLEFIX NETWORK SKB IPV6 KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Remote reachable / network-triggerable: +2
  The affected path is VXLAN transmit packet processing. It is not a public Internet style remote bug in typical deployments, but it can be influenced by network-adjacent traffic entering a VXLAN bridge or overlay path.

* Memory corruption, Weak/indirect corruption candidate: +1
  The bug can leave network headers partly in non-linear skb fragments while later code reads `arp_hdr()`, `ipv6_hdr()`, or `ip_hdr()` as if the header were linear. This supports an invalid read / OOB-read style concern, but not an OOB write, UAF, type confusion, or arbitrary write.

* Memory layout invariant restoration: +1
  The patch restores the required relationship between `skb->data`, `skb_network_offset(skb)`, and the requested header length by replacing `pskb_may_pull()` with `pskb_network_may_pull()`.

* Reliable kernel crash / strong DoS: +1
  Direct header dereference after insufficient skb linearization can plausibly lead to kernel crash or packet-processing failure.

* Common networking packet-processing path: +1
  VXLAN is a common overlay networking datapath in data-center, virtualization, and tenant-network deployments.

Subtract:

* Hard or configuration-dependent trigger: -1
  Practical triggering requires a non-linear skb shape plus affected VXLAN features such as ARP reduction, IPv6 ND handling, or MDB processing.

Paranoid-only adjustment:

* Confidentiality or integrity concern from invalid read / wrong header interpretation: +1 total
  Limited C/I concern is defensible for manual review sensitivity, but there is no evidence of attacker-controlled write, object reuse, callback control, or privilege escalation.

Not awarded:

* No Strong LPE plausibility.
* No strong memory corruption primitive.
* No Dirty-Pipe-like page-cache or shared-page ownership violation.
* No local high-control kernel API bonus.

## 3. Reachability analysis

A network-adjacent attacker may influence the affected path if traffic can enter a bridge, tenant network, or overlay path that transmits through an affected VXLAN device. No local account on the target is necessarily required in that deployment model.

The issue is not generally Internet reachable because VXLAN is normally deployed inside data-center, virtualization, tenant, or trusted overlay networks. The path also depends on specific VXLAN handling features and on skb non-linearity, so exploitation is not a trivial packet-to-crash path in every configuration.

Namespaces and containers may matter if an untrusted tenant can inject traffic into a VXLAN-backed bridge or overlay. Creating or configuring the VXLAN device itself usually requires administrative privileges, but triggering the datapath may not.

Call-site confidence: high. The changed call sites are visible in `vxlan_xmit()`, `arp_reduce()`, and `vxlan_mdb_entry_skb_get()`.

## 4. Severity interpretation

This is best treated as an Actionable Moderate issue rather than an ordinary auto-closed Moderate. The patch affects packet header validation in a networking datapath and the bug can plausibly cause invalid reads or kernel crash from network-adjacent traffic.

The realistic impact is primarily DoS. The theoretical memory-corruption concern is limited to invalid header reads caused by insufficient skb linearization. There is no supported path to privilege escalation, arbitrary write, UAF reclaim, or strong confidentiality disclosure from the supplied patch.

## 5. One-sentence report phrase

VXLAN transmit processing used `pskb_may_pull()` without accounting for the MAC-to-network-header offset, allowing specially shaped non-linear skb traffic to leave network headers partially non-linear and potentially trigger invalid header reads or kernel crash in affected VXLAN proxy or MDB paths.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a network-adjacent packet-processing bug with plausible invalid reads and DoS impact, and the affected VXLAN datapath may be reachable by untrusted tenant or internal network traffic in real deployments.

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

Patch: vxlan: use pskb_network_may_pull() for transmit path header pulls
Commit: 94dee751aad627b3645d424b5d0c736d394573e9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=94dee751aad627b3645d424b5d0c736d394573e9

Commit description:

In vxlan_xmit(), arp_reduce(), and vxlan_mdb_entry_skb_get(), pskb_may_pull() was
being called to verify the availability of network layer headers (ARP, IPv6/ND,
IP/IPv6 MDB keys).

However, during transmit skb->data points to the MAC header, so skb_network_offset(skb)
is ETH_HLEN (14 bytes). Using pskb_may_pull(skb, len) only checks len bytes from skb->data
rather than skb_network_offset(skb) + len, which can leave part of the network header
in non-linear frags.

Replace these remaining pskb_may_pull() calls with pskb_network_may_pull() to properly
account for the MAC header offset.

Fixes: e4f67ad ("add DOVE extensions for VXLAN")
Fixes: f564f45 ("vxlan: add ipv6 proxy support")
Fixes: 0f83e69 ("vxlan: Add MDB data path support")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: stable@vger.kernel.org
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260723144249.759100-6-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
  drivers/net/vxlan/vxlan_mdb.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=94dee751aad627b3645d424b5d0c736d394573e9

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

The original Linux kernel CVE announcement for CVE-2026-74474 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74474

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:N/I:N/A:H
  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: 5
  Paranoid ActionableScore: 6

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).