[CVE-2026-99264][MODERATE REGULAR] io_uring/net: don't retry recv on uncommitted buffers

[CVE-2026-99264][MODERATE REGULAR] io_uring/net: don't retry recv on uncommitted buffers

[AL-KERNEL]

CVE: CVE-2026-99264
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: io_uring/net: don't retry recv on uncommitted buffers
Commit: 21cb1770a56a51266ab96d4ed2a3b6979db59694
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=21cb1770a56a51266ab96d4ed2a3b6979db59694
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99264
Analysis date: Tue, 03 Nov 2026 22:42:53 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
An io_uring partial-receive retry can cause concurrent requests to overwrite the same provided user buffer, corrupting or mixing application data without demonstrated kernel-memory corruption.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-99264 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99264

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-99264	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99264 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L';CWE-362;*CWE-664;CWE-668;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L';BEST CVSS score: '5.6';DESCR 'An io_uring receive retried after a partial transfer can retain mappings to the unused tail of an incremental buffer or to unused buffers in a bundle while that memory is returned to the buffer group. A second receive can then obtain the same memory and both requests may write into it which can corrupt or mix data across requests and make the CQE inconsistent with actual buffer use. The demonstrated primitive is overlapping user buffer ownership rather than an OOB access UAF or kernel memory corruption. For the CVSS the PR:N value in the paranoid vector reflects a remote peer that needs no account on a vulnerable network service but can influence receive lengths and timing. AC:H reflects the required io_uring configuration with MSG_WAITALL and incremental or bundled provided buffers. Confidentiality integrity and availability are rated Low because consequences are limited to plausible cross request data exposure corruption or service disruption without evidence of host compromise. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 5.6 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage IMPORTANT to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 5.9 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	IO_URING  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; no floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +1 constrained overwrite/ownership violation: retry retains mappings while the same incremental-buffer tail or unused bundle buffer is returned to circulation, allowing two receives to write the same user memory.
* +1 local unprivileged trigger: ordinary io_uring, provided-buffer, and socket operations do not inherently require host-administrator privileges.
* Paranoid reachability uses +2 remote instead of +1 local: a peer can plausibly influence partial receive lengths and timing for a service already using the affected configuration.
* No heap/slab OOB write, UAF, kernel-memory corruption, arbitrary target, protected shared backing, authorization bypass, kernel crash, or cross-principal disclosure is shown.
* NEW52/B5-R does not apply: writes remain within mapped user buffers, and no retry-accumulated index escaping a heap allocation or later corrupted kernel-state consumer is shown.
* Confidentiality and integrity bonuses are withheld because no protected victim, read-back path, or cross-authority data flow is established.

3. Reachability analysis

A normal process can create the io_uring, buffer ring or bundle, socket, and receive requests. No capability, namespace privilege, host UID 0, special hardware, or prior administrator provisioning is indicated. A remote peer may shape receive completion and timing, but exploitation requires an application using MSG_WAITALL with incremental provided buffers or bundles; therefore remote reachability is retained only in the paranoid score.

4. Primitive and severity reading

The primitive is overlapping ownership of application-provided user memory: one retried receive retains a mapping while another request is handed the same storage, and both kernel receive paths can write it. This is CLASS_B data/ownership corruption, not kernel heap OOB or UAF. The shown effect is cross-request data overwrite and CQE/accounting inconsistency within the application. Cross-user disclosure, protected-file corruption, kernel compromise, and LPE remain unproven. ImportantCandidate is NO because no credible privilege or trust-boundary crossing is established; AutoDowngradeAllowed is YES.

5. One-sentence report phrase

An io_uring partial-receive retry can cause concurrent requests to overwrite the same provided user buffer, corrupting or mixing application data without demonstrated kernel-memory corruption.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm whether a concrete service permits remote peers to turn the overlap into cross-connection disclosure or corruption.

7. Call-site confidence

Call-site confidence: high

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

Patch: io_uring/net: don't retry recv on uncommitted buffers
Commit: 21cb1770a56a51266ab96d4ed2a3b6979db59694
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=21cb1770a56a51266ab96d4ed2a3b6979db59694

Commit description:

Commit 41b70df ("io_uring/net: commit partial buffers on retry")
commits ring provided buffers when a receive is going to be retried after
a partial transfer, so that another request using the same buffer group
can't be handed the memory the first one keeps receiving into. It commits
the number of bytes received so far. That does the job for a single
buffer which is consumed as a whole, but the request hangs on to all it
has mapped:

- For a buffer ring with IOU_PBUF_RING_INC only these bytes are consumed.
  The rest of the buffer stays at the head of the ring.
- For a bundle only the buffers which hold these bytes are consumed, the
  others that were peeked stay in the ring.

In both cases the next receive with that buffer group gets memory that
the retried request is still going to write to, and whoever comes last
overwrites the data of the other. What the retry fills isn't committed at
all, as the buffer list isn't known any more at that point. So the kernel
hands it out again later on, while the CQE tells the application that it
was used, and for an incremental buffer that it is done with.

The remainder can't be committed in advance: if the request ends up
receiving less, there is no way to tell the application that more was
consumed than the CQE accounts for. Complete the request with what it has
got instead of retrying it. MSG_WAITALL is no longer honoured for
receives into incremental buffers or multi buffer bundles, they can
return a short count, with the request marked as failed like for other
short MSG_WAITALL transfers.

Fixes: 41b70df ("io_uring/net: commit partial buffers on retry")
Assisted-by: LLM
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Link: https://patch.msgid.link/20261015-b4-io-uring-fixes-v1-40-c1556f5d7bf5@toxicpanda.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  io_uring/net.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=21cb1770a56a51266ab96d4ed2a3b6979db59694

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

The original Linux kernel CVE announcement for CVE-2026-99264 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99264

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:H/PR:L/UI:N/S:U/C:L/I:L/A:L
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
  The Best / paranoid CVSS score: 5.6

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).