[CVE-2026-74616][IMPORTANT] xdp: reject clones that overrun skb_shared_info tailroom

[CVE-2026-74616][IMPORTANT] xdp: reject clones that overrun skb_shared_info tailroom

[AL-KERNEL]

CVE: CVE-2026-74616
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: xdp: reject clones that overrun skb_shared_info tailroom
Commit: 58408982fa39f9758124cec169f42854d6f98f35
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=58408982fa39f9758124cec169f42854d6f98f35
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74616
Analysis date: Sat, 22 Aug 2026 14:57:10 -0400
ActionableScore: 8
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An XDP broadcast clone can exceed the skb shared-info tailroom requirement, allowing network-triggered corruption of XDP or skb metadata during XDP-to-skb conversion on systems with the affected XDP redirect_map broadcast configuration.

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

The original Linux kernel CVE announcement for CVE-2026-74616 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74616

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: IMPORTANT
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
======================================================================

CVE-2026-74616	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-131;CWE-119;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'An XDP clone can overrun the tailroom required for skb_shared_info because xdpf_clone checked the linear area against PAGE_SIZE instead of the smaller skb usable size. When such a cloned frame is converted back to an skb, build_skb_around can place skb_shared_info over live packet bytes and later writes can corrupt XDP return metadata. For the CVSS the PR:N is used because a remote sender needs only network reachability to an already configured XDP redirect_map broadcast path and does not need a local account on the victim. The issue is network reachable only when the affected interface already uses this non default XDP broadcast setup, so AC:H is used. Impact is at least denial of service via kernel memory corruption and in the worst case may allow confidentiality or integrity impact due to corruption of kernel networking metadata.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE SIMPLEFIX SKB LINUS KPANIC MEMORY PACKET 	NO	NO	checked

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

ActionableScore=8
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: **5**
* Paranoid score: **8**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative score signals:

* **Remote reachable / network-triggerable: +2**. A remote sender can potentially trigger the path by sending packets to an interface that already has an affected XDP redirect_map broadcast setup.
* **Constrained kernel buffer overwrite: +1**. The bug allows packet data to overlap the area later used for `skb_shared_info`, but the overwrite target and payload appear constrained by skb construction and metadata writes.
* **Memory layout invariant restoration: +1**. The patch restores the required invariant between XDP frame size, linear data size, and `skb_shared_info` tailroom by changing `PAGE_SIZE` to `SKB_WITH_OVERHEAD(PAGE_SIZE)`.
* **Reliable kernel crash / strong DoS: +1**. Corruption of XDP return metadata is a credible kernel crash or networking DoS path.
* **Common packet-processing path: +1**. XDP and skb conversion are central networking data-plane mechanisms, even though this specific broadcast redirect configuration is not default.
* **Legacy / non-default execution mode: -1**. Triggering requires a non-default XDP redirect_map broadcast configuration.
* **Corruption primitive highly constrained or metadata-only: -1**. The patch supports metadata corruption, but not an arbitrary write or demonstrated attacker-controlled object replacement.

Paranoid score signals:

* **Remote reachable / network-triggerable: +2**. Network packets can hit the vulnerable path once the affected XDP setup is active.
* **Memory corruption, strong corruption primitive: +2**. The patch context describes a concrete tailroom overrun where `skb_shared_info` can be placed over live packet bytes and later writes corrupt XDP return metadata.
* **Memory layout invariant restoration: +1**. The fix enforces the same tailroom constraint expected by XDP-to-skb conversion.
* **Weak LPE concern: +1**. Kernel networking metadata corruption can sometimes become more than DoS, although no controlled overwrite or reclaim primitive is shown.
* **Reliable kernel crash / strong DoS: +1**. Metadata corruption in this path can realistically crash or destabilize the kernel networking stack.
* **Common packet-processing path: +1**. This is in the packet-processing data path.
* **Integrity impact plausible: +1**. Corruption of XDP return metadata can plausibly affect kernel networking object state.
* **Legacy / non-default execution mode: -1**. Requires the affected XDP broadcast redirect path to be configured.

Call-site confidence: **medium-high**. The patch and commit describe the relevant downstream path through `__xdp_build_skb_from_frame()` and `build_skb_around()`, although the full caller graph is not included.

## 3. Reachability analysis

The trigger is remote only in deployments where an XDP program using redirect_map broadcast is already attached to the affected interface. Loading or attaching such an XDP program is normally privileged and often requires `CAP_BPF`, `CAP_NET_ADMIN`, or root-controlled setup, so this is not a generic unprivileged local BPF attack. However, once the vulnerable XDP path is configured, the packet sender does not need a local account on the victim and may only need network reachability to the interface.

This path is not default-enabled on typical systems. It is more relevant for high-performance networking deployments, custom XDP routing, filtering, or broadcast redirection setups.

## 4. Severity interpretation

This is not an ordinary Moderate resource leak or warning-only issue. The patch describes a concrete memory layout violation in which packet data can overlap the `skb_shared_info` area, leading to kernel metadata corruption during XDP-to-skb conversion.

Realistic exploitation is configuration-dependent and the corruption appears constrained, so the conservative score is Actionable Moderate. The paranoid score reaches Strong Important candidate because the bug is network-triggerable under a plausible XDP deployment and involves kernel networking metadata corruption rather than simple DoS.

## 5. One-sentence report phrase

An XDP broadcast clone can exceed the skb shared-info tailroom requirement, allowing network-triggered corruption of XDP or skb metadata during XDP-to-skb conversion on systems with the affected XDP redirect_map broadcast configuration.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**. This is network-reachable kernel memory corruption in a packet-processing path under a realistic but non-default XDP configuration, so it should not be auto-closed.

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

Patch: xdp: reject clones that overrun skb_shared_info tailroom
Commit: 58408982fa39f9758124cec169f42854d6f98f35
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=58408982fa39f9758124cec169f42854d6f98f35

Commit description:

xdpf_clone() clones broadcast copies into a single page and sets
frame_sz to PAGE_SIZE. __xdp_build_skb_from_frame() later treats that
page like a normal XDP frame and expects the usual skb_shared_info
tailroom at the end of the buffer.

The current check only rejects frames whose linear xdp_frame header,
headroom, and packet data exceed PAGE_SIZE. A source frame backed by a
larger allocation can still satisfy that check while extending into the
clone's required shared-info area. When such a clone is converted back
into an skb, build_skb_around() places skb_shared_info over live packet
bytes and later writes can corrupt XDP return metadata.

Reject clones unless their linear area fits inside
SKB_WITH_OVERHEAD(PAGE_SIZE), matching the tailroom requirement already
enforced by the XDP-to-skb conversion path.

Fixes: e624d4e ("xdp: Extend xdp_redirect_map with broadcast support")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Signed-off-by: Zhiling Zou <zhilinz@nebusec.ai>
Link: https://patch.msgid.link/6b2afef5d1738763c6965e8e466eb16e43e4f956.1785757386.git.zhilinz@nebusec.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  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=58408982fa39f9758124cec169f42854d6f98f35

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

The original Linux kernel CVE announcement for CVE-2026-74616 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74616

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:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 8

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).