[CVE-2026-64355][MODERATE 7.0] bpf: Reject fragmented frames in devmap [ Upstream

[CVE-2026-64355][MODERATE 7.0] bpf: Reject fragmented frames in devmap [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64355
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Reject fragmented frames in devmap [ Upstream
Commit: 47baddc856ae7e93a565dd9deeb797999b179466
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=47baddc856ae7e93a565dd9deeb797999b179466
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64355
Analysis date: Sat, 25 Jul 2026 09:13:33 -0400
ActionableScore: 5
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-2026-64355 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64355

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-2026-64355	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-125;*CWE-787;CWE-908;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A memory safety issue in the BPF devmap broadcast clone path can occur when fragmented native XDP frames are cloned. The clone copies only the linear xdp_frame data while fragment metadata lives outside the linear area, so the cloned frame can keep XDP_FLAGS_HAS_FRAGS without valid skb_shared_info metadata. During frame return, the free path may interpret uninitialized tail data as fragment metadata and perform an out-of-bounds access. For the CVSS the PR:N because an attacker only needs packet reachability to an already configured XDP devmap broadcast path and does not need local code execution on the victim. The attack is not a generic public Internet service scenario and is more likely in local or data center networks where XDP and devmap redirects are deployed. Impact is at least denial of service via kernel crash. In the paranoid interpretation, the out-of-bounds access in the frame return path is treated as a memory corruption candidate with possible confidentiality and integrity impact, so this should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	OOB BPF SIMPLEFIX SKB PACKET  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

1. **ActionableScore**
* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

2. **Signal breakdown**
* Remote reachable / network-triggerable: +2. A packet can trigger the vulnerable XDP devmap broadcast clone path if the target already has this XDP/devmap configuration active.
* Memory corruption, weak/indirect corruption candidate: +1. The clone can preserve `XDP_FLAGS_HAS_FRAGS` without valid `skb_shared_info`, causing bogus metadata interpretation and OOB access during frame return.
* Memory layout invariant restoration: +1. The patch restores the invariant between linear frame data and fragment metadata by rejecting fragmented/nonlinear frames before clone.
* Reliable kernel crash / strong DoS: +1. The described OOB access during frame return is a credible kernel crash path.
* Common packet-processing path: +1. This is in the XDP/network packet-processing datapath, though not in the generic TCP/IP receive path.
* Rare AND difficult-to-reach configuration: -1. Requires XDP devmap broadcast redirect and fragmented native XDP or nonlinear generic XDP frames.
* Corruption primitive constrained or metadata-only: -1. The patch does not show attacker-controlled overwrite, reclaim, callback control, or arbitrary read/write.
* Paranoid-only weak LPE concern: +1. Bogus `skb_shared_info` interpretation in a free/return path may affect page/refcount handling, but no practical privilege-escalation primitive is demonstrated.

3. **Reachability analysis**
Triggering does not require loading BPF if the vulnerable XDP/devmap broadcast setup already exists, so packet reachability to that datapath can be enough. Creating or attaching the XDP/BPF/devmap configuration normally requires root, `CAP_BPF`, `CAP_NET_ADMIN`, or equivalent privileges, so no local unprivileged BPF API bonus is awarded. This is not a generic public Internet service scenario. Realistic exposure is more likely in local, L2, data-center, or high-performance networking environments using XDP redirect/broadcast.

4. **Severity interpretation**
This is stronger than an ordinary Moderate because the patch describes a concrete memory-safety failure in a packet-processing path, not just validation cleanup. Conservatively, the demonstrated impact is network-adjacent DoS via kernel crash. The paranoid interpretation treats the invalid fragment metadata in the frame return path as a weak corruption candidate, but there is no demonstrated arbitrary write, reclaim primitive, or reliable LPE chain, so this remains Actionable Moderate rather than a strong Important classification.

5. **One-sentence report phrase**
A fragmented XDP frame cloned through BPF devmap broadcast can keep frag flags without valid fragment metadata, allowing packet-triggered OOB access during frame return and causing at least a kernel crash in configured XDP deployments.

6. **Manual review recommendation**
MANUAL CHECK REQUIRED. The issue is network-triggerable in configured deployments and involves OOB access from invalid fragment metadata in a kernel packet free/return path, so it should not be auto-closed even though the practical LPE evidence is weak.

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

Patch: bpf: Reject fragmented frames in devmap [ Upstream
Commit: 47baddc856ae7e93a565dd9deeb797999b179466
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=47baddc856ae7e93a565dd9deeb797999b179466

Changed files:
  kernel/bpf/devmap.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=47baddc856ae7e93a565dd9deeb797999b179466

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

The original Linux kernel CVE announcement for CVE-2026-64355 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64355

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:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 4
  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: 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).