[CVE-2026-74560][LOW] xsk: fix buffer leak in xsk_drop_skb() for AF_XDP multi-buffer Tx [ Upstream

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

CVE: CVE-2026-74560
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: xsk: fix buffer leak in xsk_drop_skb() for AF_XDP multi-buffer Tx [ Upstream
Commit: 05e283466b86e0b25a5209a3eafe87aa9886064a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=05e283466b86e0b25a5209a3eafe87aa9886064a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74560
Analysis date: Sat, 15 Aug 2026 15:50:38 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
AF_XDP multi-buffer Tx can permanently lose UMEM buffer ownership when partially built skbs are dropped without publishing consumed descriptors to the completion queue, causing local dataplane denial of service through buffer exhaustion.

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

The original Linux kernel CVE announcement for CVE-2026-74560 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74560

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-2026-74560	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-772;CWE-404;*CWE-664;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 multi-buffer Tx can lose buffer ownership when xsk_drop_skb handles a partially built skb after descriptors were already consumed from the TX ring. The affected path cancels completion queue reservations instead of publishing the consumed buffer addresses, so userspace may permanently lose track of those UMEM buffers. This is a resource leak in the AF_XDP Tx buffer lifecycle rather than a UAF or general kernel memory corruption primitive. For the CVSS the PR:L because a local process with AF_XDP Tx access is needed to prepare descriptors and trigger the drop paths. The issue is not directly network reachable and is not triggered by packet traffic alone. Impact is denial of service for the affected AF_XDP socket or application due to buffer exhaustion, with no supported confidentiality or integrity impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	OOB DEADLOCK LEAK ERRORPATH SKB IMPROVEONLY MEMORY 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
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ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Triggered positive signals:

* Local trigger: +1. A local process with AF_XDP Tx access can prepare descriptors and hit the partial multi-buffer skb drop paths.
* Availability impact realistic: +1. Lost UMEM buffer ownership can exhaust buffers for the affected AF_XDP socket or dataplane application.

Triggered negative or limiting signals:

* Rare / configuration-dependent path: -1 in the conservative score. This requires AF_XDP multi-buffer Tx usage and relevant application setup, not a default kernel path for most systems.
* No remote reachable signal. Packet traffic alone is not enough; the issue is in local AF_XDP Tx ring handling.
* No memory corruption signal. The patch shows a buffer ownership / completion queue accounting leak, not UAF, OOB write, double free, type confusion, or arbitrary write.
* No LPE signal. There is no supported privilege escalation primitive.
* No reliable kernel crash signal. The impact is buffer loss and application or dataplane DoS, not a demonstrated host-wide panic.

Call-site confidence: high. The commit describes all three affected xsk_drop_skb() callers and the diff directly changes the skb destruction and CQ publication behavior.

## 3. Reachability analysis

The bug is reachable by a local process that can use AF_XDP multi-buffer Tx and control the TX descriptors enough to trigger partial skb drop paths such as oversized packets, invalid descriptors, or socket close with an incomplete skb. Namespace or container impact depends on whether the environment delegates AF_XDP, XDP setup, or relevant network capabilities to the workload. In typical production deployments, AF_XDP is used by specialized packet-processing applications rather than arbitrary users. The path is not directly network-triggerable and is not a default exposed remote attack surface.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource leak, not an Important-class kernel vulnerability. The theoretical worst case is sustained buffer exhaustion in an AF_XDP dataplane, but the patch does not support memory corruption, privilege escalation, confidentiality impact, or integrity impact. The paranoid score remains low because the issue is constrained to AF_XDP buffer lifecycle accounting.

## 5. One-sentence report phrase

AF_XDP multi-buffer Tx can permanently lose UMEM buffer ownership when partially built skbs are dropped without publishing consumed descriptors to the completion queue, causing local dataplane denial of service through buffer exhaustion.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can usually be auto-closed or handled as low-priority Moderate unless AF_XDP multi-buffer Tx is used in a critical production dataplane where buffer exhaustion would have high operational impact.

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

Patch: xsk: fix buffer leak in xsk_drop_skb() for AF_XDP multi-buffer Tx [ Upstream
Commit: 05e283466b86e0b25a5209a3eafe87aa9886064a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=05e283466b86e0b25a5209a3eafe87aa9886064a

Changed files:
  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=05e283466b86e0b25a5209a3eafe87aa9886064a

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

The original Linux kernel CVE announcement for CVE-2026-74560 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74560

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: 1
  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).