[CVE-2026-53321][MODERATE REGULAR] io_uring/napi: cap busy_poll_to 10 msec [ Upstream

[CVE-2026-53321][MODERATE REGULAR] io_uring/napi: cap busy_poll_to 10 msec [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53321
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: io_uring/napi: cap busy_poll_to 10 msec [ Upstream
Commit: 39767f944a8c9e696566c37ad5b20131406c4b8d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=39767f944a8c9e696566c37ad5b20131406c4b8d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53321
Analysis date: Fri, 26 Jun 2026 16:59:28 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-53321 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53321

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-53321	MODERATE	CHECK	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-400;CWE-770;CWE-834;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'io_uring NAPI busy polling could be configured with an excessively large busy_poll_to value, allowing a local process to spend too much time spinning without conditional rescheduling. This can trigger stuck task or preemption complaints and may degrade CPU availability while the busy poll loop runs. For the CVSS the PR:L is used because triggering requires local code execution through an io_uring control interface, but does not require full administrative privileges in the typical case. The issue is not directly network reachable because packet traffic alone does not configure the timeout. Impact is denial of service through CPU starvation or soft lockup style behavior, with no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 3)	YES	SIMPLEFIX IO_URING  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=2

1. ActionableScore
* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Local unprivileged trigger: +1. A local process using io_uring NAPI registration can supply an excessive busy_poll_to value.
* Availability impact realistic: +1. The issue can cause excessive CPU spinning and stuck task or preemption complaints.
* Paranoid only, reliable kernel crash / strong DoS: +1. If repeated or combined with system policy such as panic_on_warn, this could become a stronger local DoS, but the patch itself does not show a guaranteed crash.
* No memory corruption: +0. The patch only caps a timeout value and does not indicate UAF, OOB access, double free, stale pointer use, or overwrite.
* No privilege escalation plausible: +0. There is no shown primitive for LPE.
* No confidentiality or integrity impact: +0. The impact is CPU availability only.

3. Reachability analysis
A local user or local process with access to io_uring and the NAPI busy poll registration path can trigger the condition by configuring an excessive busy_poll_to value. This is not network-triggerable by packets alone because the attacker must configure the io_uring control interface locally. Namespaces or containers may matter if io_uring is available inside the container, but this still remains a local resource-exhaustion style issue. The affected feature is in io_uring, a common subsystem, but the NAPI busy poll path is a specific optional use case.

4. Severity interpretation
This behaves like ordinary Moderate or Low-like local DoS, not Important. The theoretical worst case is CPU starvation or soft lockup style behavior if the busy poll loop runs too long without rescheduling. There is no realistic evidence of memory corruption, privilege escalation, information disclosure, or persistent cross-boundary impact.

5. One-sentence report phrase
An uncapped io_uring NAPI busy_poll_to value can let a local process spin in busy polling long enough to trigger stuck task or preemption complaints, causing a local denial of service without evidence of memory corruption or privilege escalation.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. This is a timeout cap / resource-exhaustion fix with local reachability only and no concrete memory corruption, security-boundary bypass, or LPE primitive.

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

Patch: io_uring/napi: cap busy_poll_to 10 msec [ Upstream
Commit: 39767f944a8c9e696566c37ad5b20131406c4b8d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=39767f944a8c9e696566c37ad5b20131406c4b8d

Changed files:
  io_uring/napi.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=39767f944a8c9e696566c37ad5b20131406c4b8d

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

The original Linux kernel CVE announcement for CVE-2026-53321 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53321

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: 2
  Paranoid ActionableScore: 3

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).