[CVE-2026-64580][MODERATE 7.0] xfrm6: clear dst.dev on error to avoid double netdev_put in xfrm6_fill_dst() [ Upstream

[CVE-2026-64580][MODERATE 7.0] xfrm6: clear dst.dev on error to avoid double netdev_put in xfrm6_fill_dst() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64580
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: xfrm6: clear dst.dev on error to avoid double netdev_put in xfrm6_fill_dst() [ Upstream
Commit: df6856c2dda9187601d29b5fbd7a81b3b178cedf
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=df6856c2dda9187601d29b5fbd7a81b3b178cedf
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64580
Analysis date: Wed, 05 Aug 2026 05:13:34 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-64580 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64580

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.

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

CVE-2026-64580	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-911;*CWE-672;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'xfrm6_fill_dst can release a net_device reference on an error path but leave dst.dev pointing to the same device. A later dst_destroy can call netdev_put again on that stale dst.dev value, causing a double reference release and net_device refcount corruption. This is reachable from local IPv6 output paths such as udpv6_sendmsg when XFRM policy and device state hit the in6_dev_get failure path. For the CVSS the PR:L is used for the paranoid score because a local unprivileged process may be able to trigger packet output when the XFRM configuration already exists, even though creating or changing XFRM policy normally requires administrative privileges. The issue is not directly network reachable by incoming packet traffic. Impact is at least local denial of service via ref_tracker warnings, unregister_netdevice stalls, or kernel instability. In the worst defensible case, the double reference release is a memory lifetime bug and may allow broader confidentiality or integrity impact if it can be shaped into a use-after-free.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE OOB DANGER ERRORPATH UAF NETWORK HARDWARE IPV6 KPANIC 	NO	NO	checked

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

ActionableScore=6
ActionableScoreLower=4

1. ActionableScore
* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**

2. Signal breakdown
* Local unprivileged trigger: +1. A local process can plausibly reach the path through IPv6 output such as udpv6_sendmsg when XFRM policy is already configured.
* Memory corruption, weak/indirect corruption candidate: +1. The bug is a stale dst.dev after netdev_put, causing a later second put rather than a demonstrated arbitrary write or controlled reclaim.
* Real lifetime corruption: +1. This is a net_device reference lifetime bug with double reference release and refcount underflow behavior.
* Reliable kernel crash / strong DoS: +1. The report shows ref_tracker WARNING and unregister_netdevice waiting for the device to become free.
* Availability impact realistic: +1 in paranoid scoring. The unregister_netdevice stall can persist beyond a transient warning and affect network device teardown.
* Confidentiality impact plausible: +1 in paranoid scoring only. If the refcount corruption can be shaped into stale object reuse, limited disclosure cannot be fully excluded.
* Integrity impact plausible: +1 in paranoid scoring only. Refcount lifetime bugs can sometimes become UAF style corruption, but no controlled overwrite is shown.
* Hard or unreliable condition: -1. Triggering requires the xfrm6_fill_dst error path where in6_dev_get returns NULL, plus suitable XFRM and IPv6 state.

3. Reachability analysis
The bug is not directly remote packet-triggerable. The visible call trace goes through local IPv6 send paths, so a local user may trigger packet output if relevant XFRM policy and device state already exist. Creating or changing XFRM policy normally requires CAP_NET_ADMIN, but triggering the already configured path may not. Network namespaces may reduce the practical privilege barrier if XFRM and IPv6 configuration is delegated, but this is not a default unprivileged configuration. XFRM/IPsec is not universal, but it is a real networking subsystem and should not be treated as a rare unreachable path.

4. Severity interpretation
This is above ordinary Moderate because it is a real refcount lifetime bug in networking code, not just a warning cleanup. The demonstrated impact is mainly local DoS through ref_tracker warnings, device teardown stalls, or kernel instability. The paranoid interpretation treats the double netdev_put as a UAF candidate, but the patch does not show attacker-controlled reclaim, object replacement, callback control, or arbitrary write. Therefore it is best handled as Actionable Moderate requiring manual review, not automatically as Important.

5. One-sentence report phrase
A local IPv6 output path with XFRM state can hit an error path in xfrm6_fill_dst where dst.dev remains set after netdev_put, causing a later double netdev_put and net_device refcount lifetime corruption with DoS and possible UAF concern.

6. Manual review recommendation
MANUAL CHECK REQUIRED. This is a refcount lifetime bug in XFRM networking code with a plausible UAF candidate, even though the currently demonstrated impact is primarily DoS.

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

Patch: xfrm6: clear dst.dev on error to avoid double netdev_put in xfrm6_fill_dst() [ Upstream
Commit: df6856c2dda9187601d29b5fbd7a81b3b178cedf
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=df6856c2dda9187601d29b5fbd7a81b3b178cedf

Changed files:
  net/xfrm/xfrm_device.c
  net/ipv6/xfrm6_policy.c
  net/ipv6/udp.c
  lib/ref_tracker.c
  net/core/dst.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=df6856c2dda9187601d29b5fbd7a81b3b178cedf

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

The original Linux kernel CVE announcement for CVE-2026-64580 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64580

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: 4
  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).