[CVE-2026-74708][LOW] xsk: validate launch-time metadata size [ Upstream

[CVE-2026-74708][LOW] xsk: validate launch-time metadata size [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74708
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: xsk: validate launch-time metadata size [ Upstream
Commit: af511afa1d2977f384044df78d6fbf9fba653f7a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af511afa1d2977f384044df78d6fbf9fba653f7a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74708
Analysis date: Sat, 22 Aug 2026 16:07:44 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
AF_XDP Tx metadata validation could accept launch-time metadata when the registered metadata area was too small, allowing limited out-of-declared-metadata reads and inconsistent flag handling by a local AF_XDP user, with impact limited to incorrect Tx metadata processing.

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

The original Linux kernel CVE announcement for CVE-2026-74708 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74708

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: LOW
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-2026-74708	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	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-20;CWE-125;CWE-362;CWE-367;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 Tx metadata validation could accept XDP_TXMD_FLAGS_LAUNCH_TIME even when the registered metadata area is too small to contain the full request.launch_time field. This can make the transmit path read metadata from bytes outside the declared metadata area and can also allow inconsistent processing if user space changes meta flags concurrently. For the CVSS the PR:L is used because a local process with access to AF_XDP and Tx metadata setup is required to trigger the condition. The issue is not directly network reachable and is driven by a local socket and UMEM metadata interface rather than by incoming packets. Impact is expected to be low and limited to incorrect transmit metadata handling or limited local data interpretation effects, with no clear evidence of kernel memory corruption, privilege escalation, or system wide crash.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	REMOTE OOB SKB HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

* Local trigger: +1
  A local process that can use AF_XDP Tx metadata can provide the metadata flags and metadata length.

* Weak validation / limited read-only OOB style concern: +1
  `XDP_TXMD_FLAGS_LAUNCH_TIME` could be accepted when `tx_metadata_len` did not cover the full `request.launch_time` field. This may read bytes outside the declared metadata area, but the read is from the AF_XDP user/UMEM buffer area rather than arbitrary kernel memory.

* Constrained metadata-only impact: -1
  The affected data is Tx metadata interpretation. No UAF, double free, OOB write, arbitrary write, refcount abuse, callback control, or attacker-controlled kernel object replacement is shown.

* Limited integrity impact plausible: +1
  Incorrect or inconsistent metadata flags could affect launch-time or completion metadata decisions, but this is limited to packet metadata behavior.

No points for remote reachability, strong DoS, generic memory corruption, privilege escalation, page-cache corruption, or security-boundary bypass.

## 3. Reachability analysis

The bug is local to AF_XDP Tx metadata handling. It is not triggered by incoming network packets alone. A process must be able to create or use an AF_XDP socket and provide Tx metadata. In many production configurations, XDP or AF_XDP setup is controlled by privileged networking components or requires capabilities such as `CAP_NET_ADMIN`, so this should not be treated as broadly unprivileged by default. Namespace or service delegation could make the interface reachable to a less privileged process, but the patch does not show a stronger primitive even in that case.

Call-site confidence: high. The relevant validation helper and its use in `xsk_skb_metadata()` are visible in the supplied patch.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like validation bug rather than an Important-class kernel vulnerability. The theoretical concern is a metadata boundary mismatch and a flags TOCTOU issue, but the realistic evidence points to incorrect AF_XDP Tx metadata processing only. There is no demonstrated kernel memory corruption, no reliable crash path, no confidentiality leak from kernel memory, and no plausible privilege escalation primitive supported by the patch.

## 5. One-sentence report phrase

AF_XDP Tx metadata validation could accept launch-time metadata when the registered metadata area was too small, allowing limited out-of-declared-metadata reads and inconsistent flag handling by a local AF_XDP user, with impact limited to incorrect Tx metadata processing.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for urgent security triage unless the affected product explicitly exposes AF_XDP Tx metadata to untrusted local users and has evidence of a stronger downstream crash or corruption primitive.

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

Patch: xsk: validate launch-time metadata size [ Upstream
Commit: af511afa1d2977f384044df78d6fbf9fba653f7a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af511afa1d2977f384044df78d6fbf9fba653f7a

Changed files:
  include/net/xdp_sock_drv.h
  net/xdp/xsk.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=af511afa1d2977f384044df78d6fbf9fba653f7a

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

The original Linux kernel CVE announcement for CVE-2026-74708 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74708

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: unknown
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).