[CVE-2026-74707][MODERATE 7.0] xsk: validate metadata when processing requests [ Upstream

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

CVE: CVE-2026-74707
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: xsk: validate metadata when processing requests [ Upstream
Commit: 5fd121971912dee2f5af1efec64462ac722deb17
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5fd121971912dee2f5af1efec64462ac722deb17
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74707
Analysis date: Sat, 22 Aug 2026 12:02:47 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
AF_XDP zero-copy TX metadata can be changed by userspace between validation and driver use, allowing a local AF_XDP user to bypass metadata checks for hardware offload requests with possible packet integrity and availability impact.

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

The original Linux kernel CVE announcement for CVE-2026-74707 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74707

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: NO

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-2026-74707	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:N/I:L/A:H';CWE-367;*CWE-20;CWE-362;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.3';DESCR 'AF_XDP zero copy TX metadata is validated while descriptor context is obtained, but the same user controlled metadata can be read again later when the driver prepares the hardware request. A local user controlling an AF_XDP UMEM can race the validation window and change flags or request fields after the first validation, which can bypass checks for TX metadata features such as launch time, timestamp, or checksum offload. For the CVSS the PR:L value is used because reliable triggering requires local code execution and access to an AF_XDP socket or a delegated networking context, not full host root privileges. The issue is not directly network reachable. Impact is at least validation bypass with possible malformed TX offload requests, packet integrity effects, driver or NIC error paths, and local denial of service. There is no direct evidence of a UAF or OOB write primitive in this patch, so the base score keeps C:N and only limited integrity and availability impact. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	REMOTE OOB INIT NETWORK DMAorINTERRUPT HARDWARE PACKET  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged or low privileged trigger: +1. Triggering requires local code controlling an AF_XDP socket, UMEM, descriptors, and TX metadata. This is not remote network input.
* Local high-control kernel data-plane API: +1. AF_XDP zero-copy gives userspace fine grained control over packet buffers, descriptors, and metadata observed by driver TX paths.
* Integrity impact plausible: +1. The bug can bypass validation of TX metadata flags and request fields, potentially affecting checksum, timestamp, or launch-time offload behavior.
* Hard or unreliable race: -1. The issue is a TOCTOU window between metadata validation and later metadata use.
* Availability concern: +1. Malformed or inconsistent hardware offload requests may plausibly cause driver or NIC error paths, but no direct kernel crash primitive is shown.

Paranoid additional interpretation:

* Common networking packet-processing path: +1. The affected helper is used by several AF_XDP zero-copy TX driver paths including igc, mlx5, stmmac, and libeth users.
* No strong memory corruption signal is awarded. The patch does not show UAF, OOB write, double free, arbitrary write, stale callback, or attacker-controlled object replacement.
* No LPE signal is awarded. Privilege escalation is not strongly supported by the patch.

Call-site confidence: high. The patch shows direct call sites in multiple zero-copy TX drivers and changes the common xsk_tx_metadata_request helper.

## 3. Reachability analysis

A local process that can use AF_XDP zero-copy TX metadata can trigger the issue by changing userspace metadata after the descriptor context was obtained but before the driver prepares the hardware request. Namespace and deployment details matter. In typical production setups, AF_XDP and XDP attachment are often controlled by privileged networking services or delegated network namespaces, so this is better treated as PR:L or delegated local access rather than fully remote or PR:N. The path is not directly network reachable from incoming packets. Realistic exploitation requires AF_XDP zero-copy TX, metadata support, and a driver path that consumes these metadata operations.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an Important kernel vulnerability. The practical issue is a local TOCTOU validation bypass in a high-control networking data path, with plausible packet integrity effects and possible driver/NIC availability consequences. However, the patch does not demonstrate a concrete memory corruption primitive, kernel pointer corruption, UAF reclaim, arbitrary write, or a clear privilege escalation path. The paranoid score is raised for manual-review sensitivity because driver-specific hardware offload behavior may have consequences not obvious from the generic helper patch.

## 5. One-sentence report phrase

AF_XDP zero-copy TX metadata can be changed by userspace between validation and driver use, allowing a local AF_XDP user to bypass metadata checks for hardware offload requests with possible packet integrity and availability impact.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

This should not be auto-closed because it is a race-based validation bypass in AF_XDP zero-copy TX metadata handling across multiple driver call sites, but it does not currently justify Important-class treatment without evidence of memory corruption, LPE, or a reliable crash primitive.

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

Patch: xsk: validate metadata when processing requests [ Upstream
Commit: 5fd121971912dee2f5af1efec64462ac722deb17
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5fd121971912dee2f5af1efec64462ac722deb17

Changed files:
  drivers/net/ethernet/intel/igc/igc_main.c
  drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
  include/net/libeth/xsk.h
  include/net/xdp_sock_drv.h
  net/xdp/xsk_buff_pool.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=5fd121971912dee2f5af1efec64462ac722deb17

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

The original Linux kernel CVE announcement for CVE-2026-74707 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74707

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:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS score: 5.3

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: 3
  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: NO
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).