[CVE-2026-74556][IMPORTANT] scsi: libiscsi_tcp: Bound SCSI Response data segment to the connection buffer [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-74556
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: scsi: libiscsi_tcp: Bound SCSI Response data segment to the connection buffer [ Upstream
Commit: c97b5265cc47775f77fd2a23d6bde0426997b233
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c97b5265cc47775f77fd2a23d6bde0426997b233
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74556
Analysis date: Sat, 15 Aug 2026 14:45:34 -0400
ActionableScore: 10
ActionableScore lower bound: 9
Actionable bucket: High-end Important / possible Critical candidate
Manual review required: YES

Summary:
A malicious or compromised iSCSI target can send an oversized SCSI Command Response data segment that overflows the fixed 8192 byte `conn->data` buffer in the Linux iSCSI TCP initiator, causing kernel memory corruption with at least DoS impact and plausible confidentiality or integrity impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74556 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74556

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-2026-74556	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-120;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '9.8';DESCR 'A kernel heap buffer overflow exists in the iSCSI TCP initiator receive path because ISCSI_OP_SCSI_CMD_RSP data can be copied into the fixed 8192 byte conn data buffer without the same DataSegmentLength bound used by other response opcodes. A malicious or compromised iSCSI target can return a SCSI Response data segment larger than 8192 bytes and up to the negotiated MaxRecvDataSegmentLength, causing attacker controlled memory corruption in the initiator kernel. For the CVSS the PR:N is used because the attacker does not need an account on the victim, but must be able to act as the configured iSCSI target or tamper with the storage TCP session. The issue is network reachable over iSCSI TCP, although iSCSI is normally deployed on isolated storage or data center networks rather than the public Internet. Impact is at least denial of service and in worst case may allow confidentiality, integrity, and availability impact due to kernel memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is High-end Important / possible Critical candidate (with actual score 10)	YES	REMOTE NETWORK HARDWARE KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=10
ActionableScoreLower=9

## 1. ActionableScore

* Conservative score: 9
* Paranoid score: 10
* Final recommended bucket: **High-end Important / possible Critical candidate**::

## 2. Signal breakdown

Conservative score signals:

* Remote reachable / network-triggerable: +2
  A malicious or compromised iSCSI target can send an oversized SCSI Command Response PDU to the Linux iSCSI TCP initiator.
* Memory corruption, Strong corruption primitive: +2
  The patch describes an overflow of the fixed 8192 byte `conn->data` kernel buffer with PDU data up to the negotiated `MaxRecvDataSegmentLength`.
* Strong LPE / kernel compromise plausibility: +2
  This is attacker-influenced kernel heap memory corruption, not only a NULL dereference or warning.
* Reliable kernel crash / strong DoS: +1
  Overflowing a kernel buffer in the receive path can realistically crash the initiator kernel.
* Confidentiality impact plausible: +1
  Kernel memory corruption can plausibly lead to disclosure in worst realistic cases.
* Integrity impact plausible: +1
  Kernel heap overwrite can plausibly corrupt kernel state.
* Important filesystem/storage path: +1
  iSCSI is a storage transport path affecting block storage access.
* Limited deployment / not normally public Internet exposed: -1
  iSCSI is usually deployed on isolated storage or data center networks, and exploitation normally requires target or MITM position.

Paranoid delta:

* Remove limited exposure penalty: +1
  In environments where the attacker controls the configured target or storage network, the trigger is direct after session establishment.

## 3. Reachability analysis

The attacker does not need a local account on the victim, but must be able to act as the iSCSI target, compromise the target, or tamper with the iSCSI TCP session. This is network-triggerable from the storage peer side, not a generic Internet-exposed listener bug.

Namespaces and containers are not the main factor here. The vulnerable code runs in the host kernel iSCSI initiator receive path. The path is not default-enabled on all systems, but it is realistic on systems using iSCSI storage. Call-site confidence: high, because the commit explicitly states that `iscsi_tcp_data_recv_prep()` copies the SCSI response data segment into the fixed `conn->data` buffer.

## 4. Severity interpretation

This behaves like an Important-class kernel vulnerability and possibly a Critical candidate in exposed storage environments. The realistic baseline impact is remote kernel crash or memory corruption from a malicious storage endpoint. The theoretical worst case includes kernel compromise because the primitive is a kernel heap buffer overflow with attacker-influenced network data.

This should not be treated as ordinary Moderate or auto-closed. The main limiting factor is deployment exposure, not weakness of the primitive.

## 5. One-sentence report phrase

A malicious or compromised iSCSI target can send an oversized SCSI Command Response data segment that overflows the fixed 8192 byte `conn->data` buffer in the Linux iSCSI TCP initiator, causing kernel memory corruption with at least DoS impact and plausible confidentiality or integrity impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is network-triggerable kernel heap memory corruption in a storage receive path, with plausible impact beyond DoS depending on heap layout and target-controlled payload constraints.

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

Patch: scsi: libiscsi_tcp: Bound SCSI Response data segment to the connection buffer [ Upstream
Commit: c97b5265cc47775f77fd2a23d6bde0426997b233
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c97b5265cc47775f77fd2a23d6bde0426997b233

Changed files:
  drivers/scsi/libiscsi_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=c97b5265cc47775f77fd2a23d6bde0426997b233

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

The original Linux kernel CVE announcement for CVE-2026-74556 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74556

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:H/I:H/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 9.8

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: 9
  Paranoid ActionableScore: 10

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).