[CVE-2026-89480][IMPORTANT] nvme-tcp: reject a read that transferred too few bytes

[CVE-2026-89480][IMPORTANT] nvme-tcp: reject a read that transferred too few bytes

[AL-KERNEL]

CVE: CVE-2026-89480
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: nvme-tcp: reject a read that transferred too few bytes
Commit: 99066cf9bba175f610ceb61a35f6fc9fbc33ff65
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=99066cf9bba175f610ceb61a35f6fc9fbc33ff65
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89480
Analysis date: Fri, 11 Sep 2026 20:51:12 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
A malicious NVMe/TCP controller can complete a read after transferring too few bytes, causing the Linux host to return stale page contents as successful read data and creating a network-adjacent information disclosure risk.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-89480 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89480

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: IMPORTANT
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-2026-89480	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-89480 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N';*CWE-200;CWE-665;*CWE-20;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N';BEST CVSS score: '8.1';DESCR 'A short data-in handling flaw in the NVMe/TCP host driver allows a controller to complete a read successfully after transferring fewer bytes than requested. The missing receive side byte count can leave part of the destination pages unchanged, so user space may receive the requested length with stale page contents in the missing range. For the CVSS the PR:N value is used because an attacker controlling or impersonating the NVMe/TCP controller does not need local privileges on the host, only reachability on the storage network. The issue is network adjacent in typical deployments because NVMe/TCP is usually used inside isolated storage or data center networks and is not normally exposed to the public Internet. Impact is primarily information disclosure and possible data integrity impact, not privilege escalation or kernel code execution.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7)	YES	REMOTE NVME ERRORPATH NETWORK LINUS TEST KPANIC 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=6
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

## 1. ActionableScore

* Raw conservative score: 6
* Conservative score: 6
* Raw paranoid score: 7
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate**::

No floor or cap was applied.

## 2. Signal breakdown

Conservative signals:

* +2: Concrete user-visible stale page contents disclosure primitive. The commit explicitly states that a 4096-byte read can complete after only 512 bytes are received, and userspace then receives 3584 bytes of whatever was already in the page.
* +2: Network-adjacent malicious controller trigger. A malicious or compromised NVMe/TCP controller can send a short C2HData response and mark the read as successful on an established NVMe/TCP connection.
* +1: Practical exploit chain is directly supported. The commit says this was reproduced with a test target and gives the concrete short-read behavior.
* +1: Important storage path. The bug is in the NVMe/TCP host read completion path, so it affects block-storage read semantics and data returned to userspace.

Paranoid additional signal:

* +1: Integrity impact is defensible in the paranoid score because successful read completion can silently return stale bytes as if they were valid storage data, corrupting the consumer-visible data stream.

Non-awarded signals:

* RealUAF not awarded. This is not a use-after-free or lifetime bug.
* Kernel memory corruption not awarded. The patch shows missing accounting and validation of received bytes, not an overwrite or controlled kernel corruption.
* Arbitrary write not demonstrated.
* Local privilege escalation not demonstrated.
* Reliable kernel crash or DoS not awarded. The primary consequence is stale data disclosure and incorrect read completion, not panic.
* Direct public Internet reachability not assumed. NVMe/TCP is normally storage-network scoped.
* Host-admin penalty not applied because host-admin-equivalent privilege is not positively established for the malicious-controller trigger on an already established connection.
* NamespaceScopedPrivilege not applicable.

## 3. Reachability analysis

The main attacker model is a malicious, compromised, or impersonated NVMe/TCP controller responding to read commands from the Linux host. Once the host has an established NVMe/TCP session, the controller can influence the vulnerable path by returning fewer bytes than requested while indicating successful completion.

Initial NVMe/TCP connection setup is commonly administrative or orchestrated by storage management, but the supplied evidence does not prove that host-admin-equivalent privilege is required for the security-relevant trigger once the controller endpoint is in use. Therefore HostAdminRequired is UNKNOWN rather than YES.

This is not treated as ordinary Internet remote exposure. NVMe/TCP targets are normally deployed on isolated storage or data-center networks. The realistic exposure is network-adjacent or trusted-internal-network access to the storage fabric.

No namespace-scoped capability path is established. No race or special timing is required. No special physical hardware is required beyond use of the NVMe/TCP host driver and an NVMe/TCP controller endpoint.

## 4. Primitive and severity interpretation

The exact primitive is acceptance of a successful NVMe/TCP read completion even though the total received C2H data length is shorter than the block request length. Because the destination buffer is not fully overwritten by controller data, userspace can receive stale page contents in the missing range.

This is not active structured-object UAF and not fixed stale storage in the UAF sense. It is a storage protocol accounting flaw that creates a concrete stale-data disclosure and semantic read-completion violation.

The demonstrated consequence is disclosure of stale page contents to userspace and incorrect storage data returned as a successful read. The speculative consequence is broader integrity damage to applications or filesystems that trust the completed read data. Privilege escalation and kernel code execution are not supported by the patch.

PrimitiveClass is CLASS_A because a concrete stale host page disclosure to userspace is established, with a malicious network-adjacent storage endpoint as the data-plane trigger. ImportantCandidate is YES because this is more than a crash-only or bookkeeping issue and affects confidentiality and storage semantics. AutoDowngradeAllowed is NO because automatically downgrading would miss a concrete stale-memory disclosure primitive in an important storage path.

Likely operational severity is Important-candidate, with exposure depending strongly on whether NVMe/TCP is enabled and whether untrusted or compromisable controllers can interact with the host.

## 5. One-sentence report phrase

A malicious NVMe/TCP controller can complete a read after transferring too few bytes, causing the Linux host to return stale page contents as successful read data and creating a network-adjacent information disclosure risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch establishes a concrete stale page contents disclosure primitive reachable through NVMe/TCP controller responses, with possible storage integrity impact and deployment-dependent attacker reachability.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: nvme-tcp: reject a read that transferred too few bytes
Commit: 99066cf9bba175f610ceb61a35f6fc9fbc33ff65
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=99066cf9bba175f610ceb61a35f6fc9fbc33ff65

Commit description:

nvme_tcp_recv_data() completes a request once the current C2HData PDU
has been consumed. Nothing compares the total bytes received against
the length the command asked for: struct nvme_tcp_request has no
receive-side counter, queue->data_remaining is per queue, and
blk_mq_end_request() completes for blk_rq_bytes(rq) unconditionally
with no residual concept anywhere above.

A controller can therefore answer a 4096-byte read with 512 bytes and
have it reported as a complete read; user space then gets 4096 bytes of
which 3584 are whatever was already in the page. I reproduced that with
a test target.

Count the bytes received and refuse to complete a successful read whose
count does not match, at the two NVME_TCP_F_DATA_SUCCESS paths and in
nvme_tcp_process_nvme_cqe(). The success test shifts req->status right
by one, because the driver keeps the wire value there and shifts it on
completion, so the check must see what the completion path will see.
Only REQ_OP_READ is checked, because there the length comes from the
sectors the request covers; a passthrough command is built by its
submitter, which picks both command and buffer, so the kernel has
nothing to compare against.

Fixes: 3f2304f ("nvme-tcp: add NVMe over TCP host driver")
Cc: stable@vger.kernel.org
Signed-off-by: Yehyeong Lee <yhlee@isslab.korea.ac.kr>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/nvme/host/tcp.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=99066cf9bba175f610ceb61a35f6fc9fbc33ff65

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

The original Linux kernel CVE announcement for CVE-2026-89480 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89480

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:A/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
  The Best / paranoid CVSS score: 8.1

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: 6
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).