[CVE-2026-74473][MODERATE 7.0] vxlan: use pskb_network_may_pull() in route_shortcircuit()

[CVE-2026-74473][MODERATE 7.0] vxlan: use pskb_network_may_pull() in route_shortcircuit()

[AL-KERNEL]

CVE: CVE-2026-74473
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: vxlan: use pskb_network_may_pull() in route_shortcircuit()
Commit: 42887be7c4cf283cce02cd0fb6411221167c8b6c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=42887be7c4cf283cce02cd0fb6411221167c8b6c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74473
Analysis date: Sat, 15 Aug 2026 10:43:12 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
VXLAN route_shortcircuit used pskb_may_pull instead of pskb_network_may_pull, allowing adjacent-network traffic with a suitable non-linear skb layout to trigger an OOB read of IPv4 or IPv6 destination header fields, with likely DoS or limited misrouting impact.

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

The original Linux kernel CVE announcement for CVE-2026-74473 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74473

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-74473	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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:L';CWE-125;*CWE-20;CWE-754;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5';DESCR 'VXLAN route_shortcircuit can read past the pulled linear portion of a non linear skb because it checked only the IP header size from skb data while skb data still points at the MAC header. As a result ip_hdr(skb) or ipv6_hdr(skb) can be dereferenced before the full network header is present in the linear buffer. A remote adjacent attacker may be able to trigger this through traffic that enters a VXLAN transmit path with route short circuit behavior and a suitable non linear packet layout. For the CVSS the PR:N is used because no account on the victim is required if the attacker can inject traffic into the relevant adjacent network path. The likely impact is denial of service or incorrect neighbor lookup behavior, with at most limited confidentiality or integrity impact from an out of bounds read. Public Internet exposure is usually not expected because VXLAN is normally used inside data center, overlay, or tenant networks.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	SIMPLEFIX NETWORK SKB LINUS IPV6  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. The issue is packet-driven in the VXLAN transmit path, but realistically adjacent or overlay-network reachable rather than public Internet reachable.
* Hard or special conditions required: -1. Triggering requires VXLAN route_shortcircuit behavior plus a suitable non-linear skb layout.
* Availability impact realistic: +1. The bug can cause invalid header access and incorrect kernel behavior, though a reliable crash is not clearly demonstrated.
* Common packet-processing path: +1. VXLAN is a networking encapsulation path used in data-center and overlay deployments, but not a universal core TCP/IP path.

Paranoid additional signals:

* Confidentiality impact plausible: +1. The primitive is a limited OOB read from skb linear data, although no user-visible disclosure path is shown.
* Integrity impact plausible: +1. The incorrectly read destination address can affect neighbor lookup behavior, but this is limited and not an arbitrary write or privilege boundary bypass.

Not awarded:

* No generic strong memory corruption. This is read-only OOB access, not UAF, double-free, OOB write, or type confusion.
* No privilege escalation signal. There is no reclaim, overwrite, callback, refcount, or arbitrary write primitive.
* No Dirty-Pipe-like or page-cache ownership violation.

## 3. Reachability analysis

An attacker needs the ability to send traffic that reaches the affected VXLAN transmit and route_shortcircuit path with a non-linear skb where the full network header is not present in the linear area. This is most plausible from an adjacent tenant, overlay, or data-center network, not from the public Internet in typical deployments. No local account on the victim is required if the attacker can inject packets into the relevant VXLAN path. Namespaces and containers may affect exposure if tenants can influence VXLAN traffic, but creating or configuring VXLAN devices is usually privileged.

Call-site confidence: high, because the changed function and dereference sites are present in the patch.

## 4. Severity interpretation

This behaves like an actionable Moderate networking bug rather than an Important-class memory corruption issue. The theoretical primitive is an out-of-bounds read from the unpulled part of a non-linear skb, but the patch does not support a write primitive, object lifetime corruption, or practical privilege escalation. The main realistic risks are incorrect neighbor lookup behavior and possible DoS or warning/crash behavior under specific packet layout conditions.

## 5. One-sentence report phrase

VXLAN route_shortcircuit used pskb_may_pull instead of pskb_network_may_pull, allowing adjacent-network traffic with a suitable non-linear skb layout to trigger an OOB read of IPv4 or IPv6 destination header fields, with likely DoS or limited misrouting impact.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED. YES REQUIRES MANUAL CHECK.

Reason: the bug is network-triggerable in a tunneling packet path and involves OOB read semantics, but current evidence supports only limited read/DoS behavior rather than strong memory corruption or LPE.

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

Patch: vxlan: use pskb_network_may_pull() in route_shortcircuit()
Commit: 42887be7c4cf283cce02cd0fb6411221167c8b6c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=42887be7c4cf283cce02cd0fb6411221167c8b6c

Commit description:

route_shortcircuit() currently calls pskb_may_pull(skb, sizeof(struct iphdr))
(or ipv6hdr), which checks if bytes are available starting from skb->data.

However, in vxlan_xmit(), skb->data points to the MAC header, so
skb_network_offset(skb) is ETH_HLEN (14 bytes). Using pskb_may_pull(skb, 20)
only checks 20 bytes from skb->data (which is 14 bytes MAC header + 6 bytes of
IP header), leaving the rest of the IP header potentially un-pulled in non-linear
frags. Subsequent dereferences of ip_hdr(skb)->daddr can read beyond the pulled
linear buffer length.

Fix this by using pskb_network_may_pull(), which adds skb_network_offset(skb) to
the length check to ensure the full network header is present in the linear buffer.

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/20260723144249.759100-5-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=42887be7c4cf283cce02cd0fb6411221167c8b6c

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

The original Linux kernel CVE announcement for CVE-2026-74473 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74473

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