[CVE-2026-74710][MODERATE REGULAR] xsk: require at least 16 bytes of TX metadata [ Upstream

[CVE-2026-74710][MODERATE REGULAR] xsk: require at least 16 bytes of TX metadata [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74710
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: xsk: require at least 16 bytes of TX metadata [ Upstream
Commit: 21b8536aee819792f1b4b38b9aacf2a073025d49
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=21b8536aee819792f1b4b38b9aacf2a073025d49
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74710
Analysis date: Sat, 22 Aug 2026 14:35:38 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / ordinary Moderate if no disclosure path is found
Manual review required: YES

Summary:
AF_XDP allowed an invalid 8 byte TX metadata length, letting the kernel read beyond the registered TX metadata area during transmit metadata processing, with local PR:L reachability and limited integrity or disclosure concern but no demonstrated privilege escalation primitive.

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

The original Linux kernel CVE announcement for CVE-2026-74710 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74710

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 REGULAR
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-2026-74710	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L';CWE-125;*CWE-20;CWE-119;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '5.3';DESCR 'AF_XDP accepted a TX metadata length of 8 bytes even though supported TX metadata requests need the flags field plus at least one 8 byte request field. This can make the kernel read past the registered TX metadata area when processing transmit metadata for an XSK UMEM. For the CVSS the PR:L is used because triggering requires a local process that can create and configure AF_XDP UMEM state, but it does not require network reachability to the host. The issue is not directly network reachable and is triggered through a local socket and UMEM registration path. Impact is expected to be limited, but the concrete out-of-bounds read makes limited confidentiality or integrity impact plausible enough for manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / ordinary Moderate if no disclosure path is found (with actual score 4)	YES	SIMPLEFIX 	YES	NO	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / ordinary Moderate if no disclosure path is found**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged or low-privilege trigger: +1
  Triggering requires a local process able to create and configure AF_XDP UMEM state. This is local PR:L rather than remote.
* Memory layout invariant restoration: +1
  The patch restores a minimum TX metadata layout invariant. Supported requests require flags plus at least one 8 byte request field, so 8 bytes is structurally invalid.
* Integrity impact plausible: +1
  The kernel may interpret bytes beyond the registered metadata area as TX metadata fields, which can cause unintended TX metadata behavior.

Paranoid additional signal:

* Limited confidentiality or availability concern: +1
  The issue is a concrete out-of-bounds read beyond the registered metadata area, but no kernel memory disclosure, write primitive, UAF, type confusion, or controlled corruption primitive is shown.

Not awarded:

* Remote reachable: +0
  This is not network-triggerable by packet input.
* Strong memory corruption: +0
  The patch shows read beyond registered metadata, not OOB write, UAF, double free, or arbitrary write.
* Strong LPE plausibility: +0
  No reclaim, overwrite, callback control, object confusion, or privilege escalation primitive is demonstrated.
* Reliable kernel crash: +0
  The commit does not show a reliable panic or system-wide crash path.

## 3. Reachability analysis

The bug is reachable through local AF_XDP UMEM registration and later TX metadata processing. A local process needs permission to use the relevant AF_XDP path and network device setup. In many deployments, practical AF_XDP use may depend on CAP_NET_RAW, CAP_NET_ADMIN, an already attached XDP program, or administrator-provided networking setup, so the trigger is not purely remote and not always available to arbitrary users. Namespaces or delegated network capabilities can lower the practical privilege requirement, so PR:L is the safer triage assumption. The path is not default Internet-exposed.

Call-site confidence: medium. The patch identifies the validation point and the downstream effect, but the exact later read sites and read-back behavior are not included in the supplied diff.

## 4. Severity interpretation

This behaves more like a borderline Moderate than an Important issue. The concrete primitive is a local bounds validation bug causing a read beyond the registered TX metadata area. Realistic exploitation evidence supports limited integrity concern and possibly limited disclosure or availability concern, but not privilege escalation or strong memory corruption. The paranoid score remains manual-review worthy because AF_XDP is a high-performance networking data path and the bug is a real OOB read condition.

## 5. One-sentence report phrase

AF_XDP allowed an invalid 8 byte TX metadata length, letting the kernel read beyond the registered TX metadata area during transmit metadata processing, with local PR:L reachability and limited integrity or disclosure concern but no demonstrated privilege escalation primitive.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a concrete OOB read in a kernel networking data path, but it should not be treated as Important without evidence of kernel memory disclosure, write corruption, reliable crash, or LPE.

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

Patch: xsk: require at least 16 bytes of TX metadata [ Upstream
Commit: 21b8536aee819792f1b4b38b9aacf2a073025d49
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=21b8536aee819792f1b4b38b9aacf2a073025d49

Changed files:
  net/xdp/xdp_umem.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=21b8536aee819792f1b4b38b9aacf2a073025d49

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

The original Linux kernel CVE announcement for CVE-2026-74710 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74710

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:L/PR:L/UI:N/S:U/C:N/I:L/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
  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: 4

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 REGULAR

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).