[CVE-2026-46315][MODERATE REGULAR] io_uring/waitid: clear waitid info before copying it to userspace

[CVE-2026-46315][MODERATE REGULAR] io_uring/waitid: clear waitid info before copying it to userspace

[AL-KERNEL]

CVE: CVE-2026-46315
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: io_uring/waitid: clear waitid info before copying it to userspace
Commit: 954518e5a4a5efc5033253f6e36fc7b9f98363a3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=954518e5a4a5efc5033253f6e36fc7b9f98363a3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46315
Analysis date: Tue, 09 Jun 2026 03:51:36 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline manual review recommended / ordinary Moderate with info leak sensitivity
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-46315 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46315

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: YES

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

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

CVE-2026-46315	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:L/I:N/A:N';*CWE-457;*CWE-200;CWE-908;BEST CVSS score: '3.3';DESCR 'An information disclosure issue exists in io_uring WAITID because io_waitid_finish can copy iw info to userspace after the wait path completes without writing wo_info. The info field is stored in reused io_kiocb command storage and was not initialized during prep, so stale kernel bytes can be exposed through the userspace siginfo result. For the CVSS the PR:L is used because a local user or process must submit IORING_OP_WAITID through io_uring, but no administrative privileges are normally required if io_uring is available. The issue is not network reachable and does not provide a direct write primitive. Impact is confidentiality loss only and may assist bypass of kernel hardening such as address randomization, but there is no direct integrity or availability impact.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / ordinary Moderate with info leak sensitivity (with actual score 4)	YES	DANGER SIMPLEFIX IO_URING  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS	YES	NO	guess

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

ActionableScore=4

1. ActionableScore
* Conservative score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / ordinary Moderate with info leak sensitivity**::

2. Signal breakdown
* Local unprivileged trigger: +1. A local process can submit `IORING_OP_WAITID` if io_uring is available.
* Local unprivileged high-control kernel data-plane API: +1. io_uring lets users submit structured async requests and reuse kernel request storage.
* Confidentiality impact plausible: +1. Uninitialized `io_waitid::info` bytes from reused `io_kiocb` storage can be copied to userspace.
* Broad/default/common subsystem: +1. io_uring is a common kernel interface, though deployments may restrict it.
* No memory corruption bonus. The patch shows an uninitialized-data disclosure, not UAF, OOB write, double-free, or type confusion.
* No integrity or availability points. The described impact is disclosure only.

3. Reachability analysis
A local unprivileged user can plausibly trigger this through io_uring by submitting `IORING_OP_WAITID`, assuming io_uring is enabled and not blocked by policy, seccomp, or distro hardening. Containers may still matter because the bug leaks host kernel memory bytes if the container can access io_uring. The path is not network reachable. The affected feature is relatively new, tied to `IORING_OP_WAITID` support from Linux 6.7+, so exposure depends on kernel version and io_uring availability.

4. Severity interpretation
This behaves like an ordinary Moderate / borderline actionable issue rather than Important. The realistic primitive is limited kernel information disclosure from uninitialized command storage. It may help defeat kernel hardening such as address randomization in a larger exploit chain, but the patch does not show write access, lifetime corruption, object confusion, or privilege escalation. Theoretical security value exists because kernel info leaks are useful, but realistic standalone impact is confidentiality only.

5. One-sentence report phrase
`IORING_OP_WAITID may copy uninitialized io_waitid result storage from reused io_kiocb memory to userspace, allowing a local user to disclose stale kernel bytes when io_uring is available.`

6. Manual review recommendation
MANUAL CHECK RECOMMENDED.
Reason: the score is below Actionable Moderate, but this is a kernel information disclosure through io_uring, so it should not be blindly auto-closed without confirming exposure, kernel version, and whether io_uring is restricted in the target environment.

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

Patch: io_uring/waitid: clear waitid info before copying it to userspace
Commit: 954518e5a4a5efc5033253f6e36fc7b9f98363a3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=954518e5a4a5efc5033253f6e36fc7b9f98363a3

Commit description:

IORING_OP_WAITID stores its result fields in struct io_waitid::info and
later copies them to userspace siginfo. The prep path initializes the
request arguments, but it does not initialize info itself.

If the wait operation completes without reporting a child event, the common
wait code can return without writing wo_info. In that case io_waitid_finish()
still copies iw->info to userspace, exposing stale bytes from the reused
io_kiocb command storage.

Clear the result storage during prep so the io_uring path matches the
regular waitid syscall, which uses a zero-initialized struct waitid_info.

Fixes: f31ecf6 ("io_uring: add IORING_OP_WAITID support")
Cc: stable@vger.kernel.org # 6.7+
Signed-off-by: Heechan Kang <gganji11@naver.com>
Link: https://patch.msgid.link/20260516184709.852814-1-gganji11@naver.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  io_uring/waitid.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=954518e5a4a5efc5033253f6e36fc7b9f98363a3

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

The original Linux kernel CVE announcement for CVE-2026-46315 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46315

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS score: 3.3

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: 4

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).