[CVE-2026-97618][MODERATE 7.0] io_uring/net: don't overconsume buffers when using MSG_TRUNC

[CVE-2026-97618][MODERATE 7.0] io_uring/net: don't overconsume buffers when using MSG_TRUNC

[AL-KERNEL]

CVE: CVE-2026-97618
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: io_uring/net: don't overconsume buffers when using MSG_TRUNC
Commit: 927d96f91c582b319d104ecf50ec935a8dc29193
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=927d96f91c582b319d104ecf50ec935a8dc29193
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97618
Analysis date: Tue, 29 Sep 2026 11:39:21 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
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-2026-97618 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97618

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 7.0
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-2026-97618	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97618 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L';CWE-682;**CWE-400;*CWE-664;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.8';DESCR 'An io_uring receive operation using MSG_TRUNC can incorrectly consume the full reported packet length from a provided buffer ring even when only part of the packet was copied. This can advance the ring beyond the buffers that were actually filled, prematurely consume available entries, and cause ENOBUFS, dropped messages, or disruption of the receiving application. A remote peer may trigger the condition by sending packets larger than the selected buffers when a network service uses io_uring provided buffer rings, incremental buffer consumption, and MSG_TRUNC. For the CVSS the PR:N value is used because an attacker only needs network access to an already configured vulnerable service and does not need a local account on the target. The required io_uring configuration and application behavior make the attack conditional and support AC:H. Impact is primarily limited denial of service. The paranoid score includes limited integrity impact because incorrect buffer accounting may cause message loss or application level data misassociation, but there is no demonstrated UAF, OOB access, arbitrary write, kernel crash, or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) 	MAYBE	IO_URING KPANIC PACKET 	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 4
* Paranoid score: 4
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Remote reachable. An external peer can supply an oversized packet to an existing service using the affected io_uring receive configuration. No privileged local control-plane action is required by that peer.
* +1 Availability impact. Incorrect ring advancement can prematurely consume available buffers, cause ENOBUFS, drop messages, or disrupt the receiving application.
* +1 Memory layout invariant restoration. The patch restores consistency between the actual copied length and the amount consumed from the provided buffer ring.
* No UAF, OOB access, overwrite, stale object, double release, or refcount mutation is established.
* No persistent kernel resource leak is established. Buffer entries are consumed incorrectly rather than permanently losing kernel references.
* No integrity point is awarded. Message loss or application accounting disruption does not establish unauthorized modification of protected kernel state or another principals data.
* No confidentiality, arbitrary-write, LPE, controlled-reclaim, or security-boundary signal is awarded.
* No common networking-core bonus is awarded because the vulnerable path requires the specific combination of provided buffer rings, incremental consumption, and MSG_TRUNC.
* No additional paranoid point is justified without inventing a memory-corruption or integrity primitive.

3. Reachability analysis

A remote peer can trigger the length mismatch when a reachable service uses io_uring provided buffer selection, incremental buffer consumption, and MSG_TRUNC with buffers smaller than the incoming packet. These are application-level prerequisites, but they do not require host-administrator configuration.

An ordinary local process can also create the relevant io_uring and socket setup without capabilities. No namespace capability, privileged sysctl, boot option, special hardware, or timing race is required. The remote security effect remains conditional on a target application actually using this uncommon receive configuration.

4. Primitive and severity interpretation

The exact primitive is a buffer-ring accounting error. The network layer returns the full packet length under MSG_TRUNC, while fewer bytes were copied, and io_uring incorrectly uses the returned length to advance buffer consumption.

This is passive bookkeeping and invalid-state behavior, not a demonstrated overwrite beyond a supplied buffer. There is no post-lifetime object use and no repeated release or refcount mutation. The demonstrated consequences are premature buffer consumption, ENOBUFS, dropped messages, and application-level receive disruption.

PrimitiveClass is CLASS_C because the patch establishes invalid accounting and limited DoS behavior without an independently useful kernel-corruption primitive. ImportantCandidate is NO because there is no memory corruption, kernel crash, authorization bypass, or privilege-escalation mechanism. AutoDowngradeAllowed is YES because no unresolved Class A or Class B primitive remains.

5. One-sentence report phrase

A remote peer may disrupt a specially configured io_uring network service by using oversized MSG_TRUNC packets to make the kernel overconsume provided buffer-ring entries, but no kernel memory corruption or privilege-escalation primitive is established.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether affected products contain network-facing services using io_uring provided buffer rings with incremental consumption and MSG_TRUNC. If no such service exists, operational exposure is low.

7. Call-site confidence

Call-site confidence: high

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

Patch: io_uring/net: don't overconsume buffers when using MSG_TRUNC
Commit: 927d96f91c582b319d104ecf50ec935a8dc29193
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=927d96f91c582b319d104ecf50ec935a8dc29193

Commit description:

When a recv/recvmsg is issued with MSG_TRUNC and the incoming packet is
larger than the provided buffer, the net layer returns the full length
of the packet rather than the number of bytes actually copied into the
buffer.  As a result, io_uring advances more of the provided buffer ring
than was actually filled.  Use the actual filled region size to consume
the buffer, but still return the full size to preserve MSG_TRUNC
semantics.

Take care with multishot, because that seems to already truncate the
consumption based on the available payload size.

This was reported in axboe/liburing#1619 .

Fixes: ae98dbf ("io_uring/kbuf: add support for incremental buffer consumption")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260728191454.1850326-1-krisman@suse.de
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
Link: https://patch.msgid.link/20260902230041.1320658-3-krisman@suse.de
[axboe: fold in size_t unsigned fix]
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=927d96f91c582b319d104ecf50ec935a8dc29193

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

The original Linux kernel CVE announcement for CVE-2026-97618 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97618

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:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS score: 4.8

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).