[CVE-2026-64190][MODERATE REGULAR] net: team: fix NULL pointer dereference in team_xmit during mode change [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-64190
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: team: fix NULL pointer dereference in team_xmit during mode change [ Upstream
Commit: 03e9405c518c4d61f28079492f252d6d4e2bac5c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=03e9405c518c4d61f28079492f252d6d4e2bac5c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64190
Analysis date: Mon, 20 Jul 2026 13:15:00 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline. Manual review recommended
Manual review required: YES

Summary:
A race in the Linux team driver during mode changes can let a concurrent transmit path call a transiently NULL transmit callback, causing a local kernel crash, with CAP_NET_ADMIN normally required but possible lower practical privilege in delegated network namespaces.

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

The original Linux kernel CVE announcement for CVE-2026-64190 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64190

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-64190	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-362;**CWE-476;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A race in the Linux team network driver can occur during a mode change while team_xmit or team_handle_frame runs on another CPU under RCU. The mode change path previously cleared team ops before restoring dummy handlers, allowing a lockless transmit path to read a NULL transmit callback and call address 0, causing a kernel crash. For the CVSS the PR:L is used for the paranoid score because some environments delegate CAP_NET_ADMIN or expose team device control to container root or service accounts rather than only full host root. The issue is not directly network reachable because the mode change is a local control plane operation, although packet transmission is needed to hit the race window. Impact is at least local denial of service via kernel crash and in worst case may allow limited confidentiality or integrity impact due to stale callback or old mode state exposure, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline. Manual review recommended (with actual score 3)	YES	KASAN NULLPTR INIT RACE NETWORK SKB KERNEL_PANIC_PLUS_UAF HARDWARE PACKET  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline. Manual review recommended**

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1
  The commit shows a NULL function pointer call from `team_xmit()` leading to an Oops at RIP 0x0.

* Real lifetime / RCU concern: +1
  The fix adds `synchronize_net()` before `exit_op()` because in-flight RCU readers may still reference old mode state.

* Hard or unreliable race / special timing required: -1
  Triggering requires a mode change racing with packet transmission on the team device.

* Requires CAP_NET_ADMIN in typical deployments: -1
  Mode change is a local network control-plane operation requiring CAP_NET_ADMIN, but this may be delegated to containers or service accounts, so I use -1 rather than full -2.

Paranoid additional signals:

* Weak LPE concern / stale callback state concern: +1
  The patch touches function callback dispatch and RCU reader lifetime. There is no demonstrated controllable callback or reclaim primitive, but the stale mode-state aspect deserves manual review.

* Common packet-processing path relevance: +1
  The crash is reached from transmit-side packet processing via `team_xmit()`, although the configuration path is local and not remotely triggered.

No strong memory corruption score is awarded because the demonstrated primitive is a NULL function pointer dereference, not attacker-controlled function pointer corruption, UAF reclaim, OOB write, or arbitrary write.

## 3. Reachability analysis

The realistic trigger requires local control over a team device mode change, normally requiring CAP_NET_ADMIN, plus concurrent packet transmission through the team interface. AF_PACKET with forced carrier makes traffic possible even when the old assumption was that no ports meant no packets in flight. This is not directly network reachable because remote packets alone do not change the team mode. Namespace or container setups may reduce the practical privilege barrier if CAP_NET_ADMIN is delegated, so the paranoid interpretation treats this as less than full host-root control.

## 4. Severity interpretation

This behaves primarily like a local DoS race in a network driver callback path. The demonstrated impact is a reliable kernel crash when the race is won. Theoretical concern exists around stale callback or old mode state under RCU, but the patch does not show attacker-controlled reuse, arbitrary write, type confusion, or controlled function pointer hijack. Therefore it is not a Strong Important candidate, but it should not be blindly auto-closed without review.

## 5. One-sentence report phrase

A race in the Linux team driver during mode changes can let a concurrent transmit path call a transiently NULL transmit callback, causing a local kernel crash, with CAP_NET_ADMIN normally required but possible lower practical privilege in delegated network namespaces.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is an RCU/callback race in a network transmit path with a demonstrated crash and some stale state concern, but no proven strong memory corruption or privilege escalation primitive.

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

Patch: net: team: fix NULL pointer dereference in team_xmit during mode change [ Upstream
Commit: 03e9405c518c4d61f28079492f252d6d4e2bac5c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=03e9405c518c4d61f28079492f252d6d4e2bac5c

Changed files:
  drivers/net/team/team_core.c
  net/core/dev.c
  net/packet/af_packet.c
  net/socket.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=03e9405c518c4d61f28079492f252d6d4e2bac5c

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

The original Linux kernel CVE announcement for CVE-2026-64190 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64190

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:H/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:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 2
  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).