[CVE-2026-74558][LOW] xsk: reclaim invalid Tx descriptors in ZC batch path [ Upstream

[CVE-2026-74558][LOW] xsk: reclaim invalid Tx descriptors in ZC batch path [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74558
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: xsk: reclaim invalid Tx descriptors in ZC batch path [ Upstream
Commit: e7ce2bad0c33471c8da4dd73dff2119a68f96f3a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e7ce2bad0c33471c8da4dd73dff2119a68f96f3a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74558
Analysis date: Sat, 15 Aug 2026 09:14:32 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
AF_XDP zero-copy multi-buffer Tx can consume invalid or oversized descriptors without returning the referenced UMEM frames through the completion ring, allowing a local AF_XDP-capable process to stall the affected Tx path or shared UMEM pool.

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

The original Linux kernel CVE announcement for CVE-2026-74558 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74558

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
======================================================================

CVE-2026-74558	LOW	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:N/I:N/A:H';*CWE-664;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'AF_XDP zero-copy multi-buffer Tx can consume invalid or oversized Tx descriptors without returning the referenced UMEM frames through the completion ring. This breaks UMEM ownership accounting and can leave frames unreclaimed by userspace, which may stall the affected Tx path or a shared UMEM pool. For the CVSS the PR:L is used because a local process must be able to create and drive an AF_XDP socket and provide crafted Tx descriptors. The issue is not directly network reachable because it is triggered by local AF_XDP control of the Tx ring rather than by received packets. Impact is primarily denial of service for the affected socket, queue, or datapath. No clear UAF, OOB access, arbitrary write, information leak, or privilege escalation primitive is visible from the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	REMOTE OOB LOCK DANGER SKB HARDWARE PACKET  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

Triggered signals:

* Local low-privileged or delegated AF_XDP trigger: +1
  A local process that can create and drive an AF_XDP zero-copy multi-buffer Tx socket can craft invalid or oversized Tx descriptors.

* Availability impact realistic: +1
  Lost UMEM frame completions can stall the affected Tx path, socket, queue, or shared UMEM pool.

Not triggered:

* Remote reachable: +0
  This is not triggered by incoming network packets alone.

* Generic memory corruption: +0
  The patch shows descriptor ownership and completion accounting issues, not UAF, OOB write, double free, type confusion, or arbitrary write.

* Privilege escalation plausible: +0
  No supported LPE primitive is visible.

* Reliable kernel crash / strong DoS: +0
  The impact is mainly datapath stall or resource ownership loss, not a demonstrated kernel panic.

* Rare / special configuration: not subtracted in the main score
  AF_XDP zero-copy multi-buffer Tx is configuration-dependent, but AF_XDP is still an ordinary local kernel networking interface in relevant deployments.

## 3. Reachability analysis

The bug is reachable by a local process that can use AF_XDP zero-copy Tx with multi-buffer descriptors and can submit malformed or oversized Tx packets. In many production deployments this is limited to privileged packet-processing services or processes with delegated networking capabilities, not arbitrary remote attackers. Namespaces or containers may matter if AF_XDP access and device queue ownership are delegated into the container, but the issue still requires local control of the Tx ring. The path is not broadly default-exposed and depends on AF_XDP, zero-copy support, suitable NIC or driver support, and multi-buffer Tx use.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource ownership bug, not an Important-class memory corruption issue. The realistic effect is denial of service or Tx datapath stall due to UMEM frames not being returned through the completion ring. Theoretical concern is limited because the patch does not show kernel object lifetime corruption, attacker-controlled overwrite, stale callback, UAF reclaim, info leak, or privilege escalation.

## 5. One-sentence report phrase

AF_XDP zero-copy multi-buffer Tx can consume invalid or oversized descriptors without returning the referenced UMEM frames through the completion ring, allowing a local AF_XDP-capable process to stall the affected Tx path or shared UMEM pool.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be handled as an ordinary Moderate / Low-like issue because the patch supports a local resource ownership and availability impact only, with no concrete memory corruption or privilege escalation primitive.

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

Patch: xsk: reclaim invalid Tx descriptors in ZC batch path [ Upstream
Commit: e7ce2bad0c33471c8da4dd73dff2119a68f96f3a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e7ce2bad0c33471c8da4dd73dff2119a68f96f3a

Changed files:
  include/net/xsk_buff_pool.h
  net/xdp/xsk.c
  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=e7ce2bad0c33471c8da4dd73dff2119a68f96f3a

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

The original Linux kernel CVE announcement for CVE-2026-74558 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74558

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:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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).