[CVE-2026-74559][LOW] xsk: drain continuation descs after overflow in xsk_build_skb() [ Upstream

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

CVE: CVE-2026-74559
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: xsk: drain continuation descs after overflow in xsk_build_skb() [ Upstream
Commit: ceb00cb87a22c42d20c39336213db2b843ca9e34
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ceb00cb87a22c42d20c39336213db2b843ca9e34
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74559
Analysis date: Sat, 15 Aug 2026 16:06:24 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like. Autoclose candidate
Manual review required: NO

Summary:
AF_XDP generic Tx multi-buffer handling could lose continuation descriptors after overflow or invalid fragmented descriptors, causing local resource loss and possible transmit path stall for an AF_XDP user, but the patch does not indicate memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-74559 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74559

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-2026-74559	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:N/I:N/A:H';CWE-755;*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 generic Tx multi buffer handling can lose continuation descriptors after xsk_build_skb() fails on an oversized packet or an invalid fragmented descriptor. The descriptors may be consumed from the Tx ring without being returned to the completion queue, leaving userspace unable to reclaim them and potentially stalling the AF_XDP socket or related transmit path. For the CVSS the PR:L is used because an attacker needs local ability to create or use an AF_XDP Tx socket and submit crafted multi buffer descriptors, but full administrator privileges are not necessarily required in delegated or containerized networking setups. The issue is not directly network reachable and is triggered through local AF_XDP control of Tx descriptors rather than incoming packet traffic. Impact is denial of service through resource loss or transmit path stall, with no concrete evidence of confidentiality impact, integrity impact, UAF, OOB write, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like. Autoclose candidate (with actual score 1)	YES	REMOTE LOCK SKB 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
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like. Autoclose candidate**

## 2. Signal breakdown

Conservative signals:

* Availability impact realistic: +1. Lost AF_XDP continuation descriptors can prevent userspace from reclaiming Tx descriptors and may stall the affected AF_XDP transmit path.
* Requires CAP_NET_ADMIN/CAP_NET_RAW or preconfigured AF_XDP access in typical deployments: -2. Creating or using this path normally requires privileged network setup or a privileged dataplane application.
* Rare and specific configuration/path: -1. The issue requires AF_XDP generic Tx multi-buffer handling, oversized fragmented packets, or invalid descriptors.

Conservative result floors at 0.

Paranoid signals:

* Local low-privileged or delegated trigger: +1. In environments where AF_XDP access is delegated to a container or service account, the trigger may be reachable without full host root.
* Local high-control dataplane API: +1. AF_XDP Tx descriptors give fine-grained userspace control over descriptor layout and multi-buffer state, but only when AF_XDP access is already available.
* Availability impact realistic: +1. Descriptor loss can reliably stall the affected socket or transmit path.
* Rare and specific AF_XDP multi-buffer path: -1.

Paranoid result: 2.

No memory corruption, UAF, OOB write, object lifetime corruption, privilege escalation, confidentiality impact, or integrity impact is supported by the patch.

## 3. Reachability analysis

The bug is triggered locally by a process that can use an AF_XDP Tx ring and submit malformed or oversized multi-buffer descriptors. It is not network reachable through incoming packet traffic. In typical deployments, AF_XDP setup is privileged or controlled by a privileged networking service, so a normal unprivileged local user usually cannot trigger it directly. Namespace or container delegation can lower the practical privilege requirement if AF_XDP access is intentionally exposed to a workload.

Call-site confidence: high, because the relevant caller path in `__xsk_generic_xmit()` and the descriptor drain logic are present in the patch.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource handling bug, not an Important-class vulnerability. The practical impact is descriptor/resource loss and possible local Tx path stall. The patch does not show memory corruption, attacker-controlled overwrite, stale pointer reuse, cross-boundary policy bypass, or LPE potential.

## 5. One-sentence report phrase

AF_XDP generic Tx multi-buffer handling could lose continuation descriptors after overflow or invalid fragmented descriptors, causing local resource loss and possible transmit path stall for an AF_XDP user, but the patch does not indicate memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED.

This can be auto-closed for urgent security triage because the issue is local, configuration-dependent, resource-loss oriented, and lacks evidence of memory corruption, privilege escalation, confidentiality impact, or integrity impact.

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

Patch: xsk: drain continuation descs after overflow in xsk_build_skb() [ Upstream
Commit: ceb00cb87a22c42d20c39336213db2b843ca9e34
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ceb00cb87a22c42d20c39336213db2b843ca9e34

Changed files:
  include/net/xdp_sock.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=ceb00cb87a22c42d20c39336213db2b843ca9e34

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

The original Linux kernel CVE announcement for CVE-2026-74559 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74559

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: 0
  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).