[CVE-2026-52989][IMPORTANT] nvmet-tcp: propagate nvmet_tcp_build_pdu_iovec() errors to its callers [ Upstream

[CVE-2026-52989][IMPORTANT] nvmet-tcp: propagate nvmet_tcp_build_pdu_iovec() errors to its callers [ Upstream

[AL-KERNEL]

CVE: CVE-2026-52989
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: nvmet-tcp: propagate nvmet_tcp_build_pdu_iovec() errors to its callers [ Upstream
Commit: 3df42a854686fa06484e37ac1a3931c8e3e3453c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3df42a854686fa06484e37ac1a3931c8e3e3453c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52989
Analysis date: Thu, 25 Jun 2026 05:21:05 -0400
ActionableScore: 8
ActionableScore lower bound: 7
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An invalid NVMe/TCP PDU length or offset can leave the receive iterator uninitialized while the queue proceeds to data receive state, allowing a network-reachable initiator on the storage network to trigger kernel DoS and plausible memory corruption.

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

The original Linux kernel CVE announcement for CVE-2026-52989 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52989

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.

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

CVE-2026-52989	IMPORTANT	CHECK	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:H';*CWE-20;*CWE-457;*CWE-787;CWE-120;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.8';DESCR 'An invalid NVMe/TCP PDU length or offset can make nvmet_tcp_build_pdu_iovec fail before cmd recv_msg msg_iter is initialized. Because the old helper returned void, callers could still switch the queue into NVMET_TCP_RECV_DATA and the socket receive loop could copy attacker controlled network data through an uninitialized iterator. For the CVSS the PR:N is used because no privileges are required on the target beyond network reachability to the NVMe/TCP target endpoint. The vector is treated as AV:A because NVMe/TCP targets are normally deployed on isolated storage or data center networks rather than the public Internet. Impact is at least denial of service via kernel crash and may include confidentiality or integrity impact because this is a plausible memory corruption candidate, not only a warning or resource leak.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) 	MAYBE	REMOTE WRITE OOB DANGER NVME ERRORPATH NETWORK LINUS KPANIC MEMORY 	-	-	checked

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

ActionableScore=8
ActionableScoreLower=7

## 1. ActionableScore

* Conservative score: 7
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**

## 2. Signal breakdown

* Remote reachable / network-triggerable: +2
  NVMe/TCP target processing is reachable over TCP when the target port is exposed to an initiator on the storage network.

* Memory corruption, weak/indirect corruption candidate: +1
  The failed bounds path can leave `cmd->recv_msg.msg_iter` uninitialized, and later receive code may copy network data through that iterator. This is stronger than a pure NULL dereference, but not enough to claim a controlled arbitrary write.

* Weak LPE concern: +1, paranoid only
  If the uninitialized iterator can reference stale or unintended kernel memory, integrity impact beyond crash is plausible, but the patch does not demonstrate a reliable reclaim or target-selection primitive.

* Reliable kernel crash / strong DoS: +1
  Invalid PDU length or offset can drive the receive path into an invalid state and plausibly crash the kernel.

* Confidentiality impact plausible: +1
  Conservative but defensible because corrupted iterator state may interact with unintended memory, though no direct disclosure primitive is shown.

* Integrity impact plausible: +1
  Network data may be written through an unintended destination iterator in the bad state.

* Important filesystem/storage path: +1
  NVMe/TCP target is a storage data-plane protocol and compromise or crash of this path is operationally significant.

No admin privilege penalty is applied because a remote initiator does not need local root on the target once the NVMe/TCP service is reachable.

## 3. Reachability analysis

A network peer that can connect to the NVMe/TCP target can plausibly trigger the bug by sending malformed or out-of-bounds PDU state that causes `nvmet_tcp_build_pdu_iovec()` to fail. The issue is not normally Internet-wide exposure, because NVMe/TCP targets are usually deployed on isolated storage or data-center networks. However, inside that network the attack does not require local code execution or administrative privileges on the target. Namespaces are not the main factor here. Exposure depends on whether `nvmet-tcp` is enabled and reachable by untrusted or compromised initiators.

## 4. Severity interpretation

This behaves above ordinary Moderate. The realistic impact is at least a network-adjacent kernel DoS against an NVMe/TCP target. The reason it becomes an Important candidate is that the receive loop may consume attacker-controlled network data through an uninitialized `iov_iter`, which is a plausible memory-corruption sink. The evidence does not justify claiming arbitrary code execution or a reliable privilege-escalation primitive, but it is strong enough to avoid auto-closure.

## 5. One-sentence report phrase

An invalid NVMe/TCP PDU length or offset can leave the receive iterator uninitialized while the queue proceeds to data receive state, allowing a network-reachable initiator on the storage network to trigger kernel DoS and plausible memory corruption.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is network-triggerable in an important storage target path and involves a plausible uninitialized destination iterator used for receiving attacker-controlled data, so it should not be treated as an ordinary crash-only Moderate without manual review.

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

Patch: nvmet-tcp: propagate nvmet_tcp_build_pdu_iovec() errors to its callers [ Upstream
Commit: 3df42a854686fa06484e37ac1a3931c8e3e3453c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3df42a854686fa06484e37ac1a3931c8e3e3453c

Changed files:
  drivers/nvme/target/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=3df42a854686fa06484e37ac1a3931c8e3e3453c

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

The original Linux kernel CVE announcement for CVE-2026-52989 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52989

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.8

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: 7
  Paranoid ActionableScore: 8

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).