[CVE-2026-45846][MODERATE REGULAR] bareudp: fix NULL pointer dereference in bareudp_fill_metadata_dst() [ Upstream

[CVE-2026-45846][MODERATE REGULAR] bareudp: fix NULL pointer dereference in bareudp_fill_metadata_dst() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45846
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bareudp: fix NULL pointer dereference in bareudp_fill_metadata_dst() [ Upstream
Commit: a0f4e4e8e0f5e24ddd83e3d1221732621cf34636
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a0f4e4e8e0f5e24ddd83e3d1221732621cf34636
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45846
Analysis date: Wed, 27 May 2026 06:15:36 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
`bareudp_fill_metadata_dst()` can dereference a NULL Bareudp socket on the IPv6 metadata path when the device is down, allowing a CAP_NET_ADMIN-equivalent OVS or tunnel control actor to trigger a kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-45846 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45846

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-2026-45846	MODERATE	CHECK	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-476;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'bareudp_fill_metadata_dst can pass a NULL socket to udp_tunnel6_dst_lookup on the IPv6 metadata path when the bareudp device is down. This can dereference sock sk and crash the kernel when an OVS action or metadata tunnel path tries to resolve the destination for that device. For the CVSS the PR:L is used for the paranoid score because CAP_NET_ADMIN or equivalent network control can be delegated to container root, reduced capability service accounts, or namespace administrators in some deployments. The issue is local control plane reachable rather than directly Internet remote. Impact is denial of service via kernel crash only, with no supported evidence of information disclosure, memory corruption, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 2)	YES	DANGER NULLPTR INIT NETWORK HARDWARE IPV6  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	checked

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

ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1. The trace shows a NULL pointer dereference in `udp_tunnel6_dst_lookup()` via `bareudp_fill_metadata_dst()`.
* Availability impact realistic: +1. The demonstrated result is a kernel crash when the metadata path is invoked while `bareudp->sock` is NULL.
* Networking / tunnel subsystem context: +1. The affected path is in Bareudp metadata destination lookup and is reachable through Open vSwitch action execution.
* Requires CAP_NET_ADMIN or equivalent in typical deployments: -2. Creating/managing Bareudp and OVS datapath actions normally requires network administration privileges.

Conservative total: 1.

Paranoid interpretation:

* Reliable kernel crash / strong DoS: +1.
* Availability impact realistic: +1.
* Networking / OVS tunnel control path: +1.
* No full CAP penalty in delegated environments: 0 penalty. CAP_NET_ADMIN or equivalent OVS control may be delegated to container root, namespace administrators, or service accounts, making practical PR:L risk plausible.

Paranoid total: 3.

No memory corruption signal is counted. The patch supports a NULL socket dereference only, not UAF, OOB write, arbitrary write, refcount corruption, or page-cache/shared-page corruption.

## 3. Reachability analysis

The crash is reached when `bareudp_fill_metadata_dst()` is called on the IPv6 metadata path while the Bareudp device is down and `bareudp->sock` has been cleared. The provided trace goes through Open vSwitch generic netlink packet execution, so practical triggering normally requires local network-control capability over OVS or tunnel configuration.

This is not directly Internet remote. A plain remote packet is not sufficient unless the system is already configured so that packet processing reaches this specific OVS/Bareudp metadata path while the device is down. Namespaces and containers matter because CAP_NET_ADMIN is often delegated, so the risk can be higher than a full-host-root-only bug in containerized environments.

## 4. Severity interpretation

This behaves like a local or delegated network-admin DoS issue, not an Important-class memory corruption vulnerability. The realistic impact is kernel crash. Theoretical privilege escalation is not supported by the patch because the primitive is a NULL pointer dereference and the fix is only a NULL check returning `-ESHUTDOWN`.

It is borderline for manual review because it involves OVS/tunnel networking control paths and delegated CAP_NET_ADMIN is common, but it should not be escalated as memory corruption or LPE without additional evidence.

## 5. One-sentence report phrase

`bareudp_fill_metadata_dst()` can dereference a NULL Bareudp socket on the IPv6 metadata path when the device is down, allowing a CAP_NET_ADMIN-equivalent OVS or tunnel control actor to trigger a kernel crash.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED.

Reason: the demonstrated impact is DoS-only, but the path involves OVS/Bareudp networking control and delegated CAP_NET_ADMIN deployments may make the trigger practical for less-than-full-root actors.

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

Patch: bareudp: fix NULL pointer dereference in bareudp_fill_metadata_dst() [ Upstream
Commit: a0f4e4e8e0f5e24ddd83e3d1221732621cf34636
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a0f4e4e8e0f5e24ddd83e3d1221732621cf34636

Changed files:
  net/ipv6/ip6_udp_tunnel.c
  drivers/net/bareudp.c
  net/openvswitch/actions.c
  net/openvswitch/datapath.c
  net/netlink/genetlink.c
  net/netlink/af_netlink.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=a0f4e4e8e0f5e24ddd83e3d1221732621cf34636

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

The original Linux kernel CVE announcement for CVE-2026-45846 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45846

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:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  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: 1
  Paranoid ActionableScore: 3

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).