[CVE-2026-81002][MODERATE 7.0] xdp: fix zero-copy frame layout

[CVE-2026-81002][MODERATE 7.0] xdp: fix zero-copy frame layout

[AL-KERNEL]

CVE: CVE-2026-81002
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: xdp: fix zero-copy frame layout
Commit: 444216dacdbebd3e52d5e704facafbb230da09e9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=444216dacdbebd3e52d5e704facafbb230da09e9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-81002
Analysis date: Fri, 11 Sep 2026 16:20:15 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-81002 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-81002

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-2026-81002	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-81002 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-787;CWE-131;CWE-119;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'An out-of-bounds write can occur in the XDP to skb path because xdp_convert_zc_to_xdp_frame can copy an AF_XDP zero-copy frame into an order-0 page while advertising PAGE_SIZE as the frame size. The copied packet can overlap the page tail reserved for skb_shared_info or use an invalid layout when metadata is present and headroom is recorded as zero. A local actor able to use AF_XDP zero-copy and redirect packets through cpumap can trigger the issue and reach skb_gro_receive where KASAN reports a slab-out-of-bounds write. For the CVSS the PR:L is used because reliable triggering normally requires local code with delegated network or BPF capabilities rather than full host root. The issue is not directly network reachable as a pure remote packet attack. Impact is at least denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact because the observed primitive is kernel heap out-of-bounds write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	REMOTE WRITE KASAN OOB SKB LINUS KPANIC MEMORY PACKET  DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	NO	NO	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5. No floor or cap changed the conservative score.
* Raw paranoid score: 6
* Paranoid score: 6. BPF/XDP privileged-control-plane paranoid cap is 6, and the raw paranoid score reaches but does not exceed it.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive conservative signals:

* +2 Strong kernel corruption primitive. The patch and KASAN trace establish a real slab out-of-bounds write in `skb_gro_receive()` caused by an invalid XDP zero-copy frame layout.
* +1 Reliable kernel crash / strong DoS. The supplied trace shows `Kernel panic - not syncing: KASAN: panic_on_warn set`.
* +1 Memory layout invariant restoration. The fix restores consistency between copied frame size, `SKB_WITH_OVERHEAD(PAGE_SIZE)`, metadata headroom, and the page tail reserved for `skb_shared_info`.
* +1 Packet-processing path. The corruption is reached through XDP/cpumap/GRO packet processing, not merely through a diagnostic or passive validation path.

Additional paranoid signal:

* +1 Weak exploitation concern. The out-of-bounds write affects kernel heap memory around active skb/GRO metadata, including possible overlap with `skb_shared_info`, and attacker-controlled AF_XDP frame layout influences reachability. This does not prove arbitrary write or LPE, but it is enough to keep the issue above ordinary DoS triage.

Negative or non-awarded signals:

* No UAF signal. This is an OOB write/layout bug, not a lifetime bug.
* No concrete repeated release/refcount signal.
* No controlled reclaim or arbitrary kernel read/write is demonstrated.
* No confidentiality or integrity point is awarded as a proven consequence. C/I remain unresolved exploitation concerns, not established impact.
* No remote reachability point. The issue is not shown to be triggerable by unauthenticated network packets alone.
* No host-admin penalty is applied because host-admin-equivalent privilege is not positively established from the supplied evidence.
* No namespace-scoped privilege credit is applied because the complete BPF/XDP/AF_XDP/cpumap setup is not proven to be attacker-obtainable inside namespaces.

3. Reachability analysis

The apparent trigger is a local AF_XDP zero-copy setup with packet redirection through cpumap, followed by GRO processing of the converted skb path.

For BPF/XDP:

* BPF/XDP program loading is normally privilege-gated by CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN, sysctls, or product policy.
* XDP attachment to a netdevice is also privilege-gated.
* AF_XDP zero-copy generally depends on driver and queue setup.
* cpumap redirection requires BPF/XDP configuration.
* The supplied input does not prove that an ordinary unprivileged user can perform the complete trigger chain.
* The supplied input also does not prove that full host root or host-admin-equivalent privilege is strictly required.
* Therefore HostAdminRequired is UNKNOWN and NamespaceScopedPrivilege is UNKNOWN.

Prior setup may be required in real deployments: AF_XDP zero-copy support, suitable driver/NIC support, XDP program attachment, and cpumap use. These are material prerequisites, but they do not erase the established kernel OOB write primitive.

Race difficulty is not relevant. This is a layout and bounds bug, not a timing race.

4. Primitive and severity interpretation

The exact primitive is a kernel heap out-of-bounds write caused by an invalid zero-copy XDP frame layout when converting an XSK packet into an order-0 page backed `xdp_frame`.

This is not fixed stale storage and not UAF. The vulnerable frame can overlap the area needed for `skb_shared_info` or place data beyond the allocated page. The demonstrated consequence is a KASAN-detected slab out-of-bounds write followed by kernel panic.

PrimitiveClass is CLASS_A because a concrete attacker-influenced OOB write in kernel heap memory is established. Stronger consequences such as arbitrary write, controlled reclaim, information disclosure, or privilege escalation are not demonstrated, so the score is kept in the 5-6 actionable range rather than 7+.

ImportantCandidate is YES because CLASS_A corruption exists and exploitation leverage beyond crash remains unresolved. AutoDowngradeAllowed is NO because automatically closing this as ordinary DoS would discard a concrete kernel heap corruption primitive.

Likely operational severity: actionable Moderate at minimum, with Strong Important review warranted if the affected product allows below-host-admin BPF/XDP/AF_XDP setup or if further analysis shows useful control over the overwritten skb/shared-info state.

5. One-sentence report phrase

A local actor able to configure AF_XDP zero-copy with XDP cpumap redirection can trigger an invalid XDP frame layout that reaches GRO processing and causes a kernel heap out-of-bounds write, leading to kernel crash and requiring manual review for possible impact beyond DoS.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch establishes a real kernel heap out-of-bounds write in a packet-processing path, and the practical privilege boundary plus exploitation leverage of the skb/shared-info corruption need product-specific review.

7. Call-site confidence

Call-site confidence: high

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

Patch: xdp: fix zero-copy frame layout
Commit: 444216dacdbebd3e52d5e704facafbb230da09e9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=444216dacdbebd3e52d5e704facafbb230da09e9

Commit description:

xdp_convert_zc_to_xdp_frame() clones an XSK packet into an order-0 page
and advertises PAGE_SIZE as its frame size.  It allows the copied frame
to occupy the page tail needed by skb_shared_info and records zero
headroom even when metadata separates the frame header from packet data.
An AF_XDP zero-copy packet redirected through cpumap can therefore make
the skb overlap skb_shared_info or place it beyond the allocated page.

Limit the copied layout to SKB_WITH_OVERHEAD(PAGE_SIZE) and include the
metadata length in frame headroom.  Redirect callers already handle a
NULL conversion result.

BUG: KASAN: slab-out-of-bounds in skb_gro_receive
Write of size 4 at addr ffff88800cf37004 by task cpumap/1/map:1/146
Call Trace:
 skb_gro_receive (net/core/gro.c:174)
 udp_gro_receive (net/ipv4/udp_offload.c:812)
 inet_gro_receive (net/ipv4/af_inet.c:1539)
 dev_gro_receive (net/core/gro.c:515)
 gro_receive_skb (net/core/gro.c:633)
 cpu_map_kthread_run (kernel/bpf/cpumap.c:395)
 kthread (kernel/kthread.c:436)
 ret_from_fork (arch/x86/kernel/process.c:164)
 ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
Kernel panic - not syncing: KASAN: panic_on_warn set ...

Fixes: b0d1bee ("xdp: implement convert_to_xdp_frame for MEM_TYPE_ZERO_COPY")
Cc: stable@vger.kernel.org
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Link: https://patch.msgid.link/20260818154516.793517-1-bestswngs@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/core/gro.c
  net/ipv4/udp_offload.c
  net/ipv4/af_inet.c
  kernel/bpf/cpumap.c
  kernel/kthread.c
  arch/x86/kernel/process.c
  arch/x86/entry/entry_64.S
  net/core/xdp.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=444216dacdbebd3e52d5e704facafbb230da09e9

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

The original Linux kernel CVE announcement for CVE-2026-81002 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-81002

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: 5
  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).