[CVE-2026-99153][IMPORTANT] scsi: libiscsi: Validate the ITT reflected in a Reject PDU

[CVE-2026-99153][IMPORTANT] scsi: libiscsi: Validate the ITT reflected in a Reject PDU

[AL-KERNEL]

CVE: CVE-2026-99153
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: scsi: libiscsi: Validate the ITT reflected in a Reject PDU
Commit: 7215a69b6456fda79c0935c2959045dff3fcaac8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7215a69b6456fda79c0935c2959045dff3fcaac8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99153
Analysis date: Fri, 30 Oct 2026 11:24:37 -0400
ActionableScore: 7
ActionableScore lower bound: unknown
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
A malicious connected iSCSI target can forge a reflected ITT to crash the initiator or falsely complete an unrelated SCSI command without transferring its data.

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

The original Linux kernel CVE announcement for CVE-2026-99153 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99153

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-2026-99153	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-99153 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC)	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-476;*CWE-672;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H';BEST CVSS score: '8.8';DESCR 'A malicious or compromised iSCSI target can place an attacker controlled ITT in the reflected header of a Reject PDU. libiscsi previously checked only that the decoded task index was within cmds_max, so the target could select an unused, free, or unrelated in flight task. This can cause a NULL pointer dereference and kernel crash, a refcount underflow on a free task, or false successful completion of an active SCSI command with its read buffer unchanged. For the CVSS the PR:N value is selected because the attacking storage peer needs network reachability and an established iSCSI connection but does not need privileges on the initiator host. AV:A is used because exploitation is limited to a reachable iSCSI storage peer rather than arbitrary Internet traffic. The base integrity impact is high because an affected command can be reported as successfully completed lacking valid transferred data. The paranoid confidentiality impact reflects the unresolved possibility that unchanged or stale buffer contents become observable, while direct UAF or arbitrary write is not proven. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 8.8 and the production ActionableScore returned 7 with recommendation Strong Important candidate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS8.5PLUS and TEMP_KPANIC_MERGE_IMPORTANT_WINS. The independent weaker Aegis shadow evaluated CVSS 7.1 and ActionableScore 5 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7)	MAYBE	KASAN OOB NULLPTR INIT LEAK KERNEL_PANIC_PLUS_UAF HARDWARE LINUS  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS8.5PLUS TEMP_KPANIC_MERGE_IMPORTANT_WINS	-	-	checked

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

ActionableScore=7
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 7.
* Conservative score: 7; no floor or cap applied.
* Raw paranoid score: 7.
* Paranoid score: 7; confidentiality and LPE theories are not scored.
* Final recommended bucket: **Strong Important candidate**::

2. Signal breakdown

* +2 — Strong active-object corruption/selection: target-controlled reflected ITT can select an unrelated task and drive `iscsi_nop_out_rsp()`/`iscsi_complete_task()` against it.
* +2 — Network-reachable malicious storage peer: a connected iSCSI target can supply the Reject PDU without privileges on the initiator host. Exposure is connection-scoped, not arbitrary Internet reachability.
* +1 — Practical exploit chain: forged ITT → unrelated in-flight SCSI task selected → command falsely completed successfully.
* +1 — Confirmed integrity effect: a 1 MiB read can report success while its destination buffer remains unwritten.
* +1 — Reliable crash/DoS: selecting an unused entry causes a NULL dereference; selecting a free task can underflow its refcount.
* No extra availability point: the same crash is already counted.
* No confidentiality point: exposure of stale buffer contents is unresolved.
* No UAF or repeated-release point: `ISCSI_TASK_FREE` identifies pool state, but the evidence does not show slab lifetime ending or a dangling allocation.
* No arbitrary write, controlled reclaim, or LPE is shown.
* B5-R does not apply: there is no retry-accumulated heap OOB write.
* B3-PENDING and B4-PENDING do not apply: this is neither shared-backing modification nor an authorization guard bypass.

3. Reachability analysis

The attacker is a malicious or compromised iSCSI target on an already established session. It controls the Reject PDU and reflected ITT but needs no host UID, capability, or host-administrator power. Prior initiator configuration is required to establish the storage relationship, limiting exposure to a trusted/network-adjacent peer. No namespace capability is relevant or established, and no race or special hardware is required.

4. Primitive and severity reading

The primitive is attacker-directed lookup and consumption of an arbitrary task-pool entry due to missing ITT validation. The selected active structured task is then completed by privileged initiator-kernel code. Proven outcomes are NULL dereference, refcount underflow, and false successful completion of an unrelated SCSI command. The storage-target/initiator trust boundary and confirmed command-integrity failure make this CLASS_A and Important-preserving. Arbitrary kernel memory write, disclosure, and privilege escalation remain unproven.

5. One-sentence report phrase

A malicious connected iSCSI target can forge a reflected ITT to crash the initiator or falsely complete an unrelated SCSI command without transferring its data.

6. Manual review advice

MANUAL CHECK REQUIRED

The patch proves attacker-selected active task consumption across the storage trust boundary with confirmed data-integrity and crash effects.

7. Call-site confidence

Call-site confidence: high

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

Patch: scsi: libiscsi: Validate the ITT reflected in a Reject PDU
Commit: 7215a69b6456fda79c0935c2959045dff3fcaac8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7215a69b6456fda79c0935c2959045dff3fcaac8

Commit description:

A Reject PDU carries a copy of the header it rejects, and
iscsi_handle_reject() takes the ITT out of that copy to find the task to
clean up:

      memcpy(&rejected_pdu, data, sizeof(struct iscsi_hdr));
      ...
      task = iscsi_itt_to_task(conn, rejected_pdu.itt);

That value is whatever the target put there. iscsi_itt_to_task() bounds
the index against cmds_max and checks nothing else, so any task in the
pool can be named, and iscsi_nop_out_rsp() then completes it.

An index that has never been used gives a NULL task->conn: the pool is
zeroed at session setup and conn is assigned only when a task is
allocated. If the task was used and returned, iscsi_complete_task() hits
its WARN_ON_ONCE(task->state == ISCSI_TASK_FREE) and the refcount
underflows. An in-flight SCSI command is completed as successful - a 1
MiB read returned 1048576 with none of its buffer written and no
warning.

Validate the reflected ITT the way iscsi_itt_to_ctask() validates a
command ITT, and require the task to be in flight and not a SCSI
command.

[    6.248477] Oops: general protection fault, probably for non-canonical address 0xdffffc000000000c: 0000 [#1] SMP KASAN NOPTI
[    6.249357] KASAN: null-ptr-deref in range [0x0000000000000060-0x0000000000000067]
[    6.249951] CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 7.2.0-rc5-ISCSI1-gf5098b6bae76 #1 PREEMPT(lazy)
[    6.250718] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[    6.251616] RIP: 0010:iscsi_nop_out_rsp.constprop.0+0x46/0x160
[    6.252043] Code: c1 ea 03 48 83 ec 08 80 3c 02 00 0f 85 f5 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 6b 58 48 8d 7d 60 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 c0 00 00 00 48 8b 45 60 48 39 c3 74 50 48 b8 00
[    6.252813] RSP: 0018:ffff88806c907b80 EFLAGS: 00010206
[    6.253042] RAX: dffffc0000000000 RBX: ffff88800607e000 RCX: ffffffff8d571a25
[    6.253345] RDX: 000000000000000c RSI: ffff88806c907c38 RDI: 0000000000000060
[    6.253642] RBP: 0000000000000000 R08: 0000000000000000 R09: fffffbfff235a504
[    6.253947] R10: 0000000000000003 R11: 7463656e6e6f6320 R12: 0000000000000000
[    6.254251] R13: 0000000000000000 R14: ffff88806c907c38 R15: 0000000000000000
[    6.254549] FS:  0000000000000000(0000) GS:ffff8880d95bc000(0000) knlGS:0000000000000000
[    6.254887] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    6.255140] CR2: 00007fc393e8ffc0 CR3: 0000000005252006 CR4: 0000000000770ef0
[    6.255439] PKRU: 55555554
[    6.255564] Call Trace:
[    6.255674]  <IRQ>
[    6.255768]  __iscsi_complete_pdu+0x18bf/0x22a0
[    6.256733]  iscsi_complete_pdu+0x54/0xa0
[    6.256905]  iscsi_tcp_data_recv_done+0xf4/0x250
[    6.257103]  iscsi_tcp_recv_skb+0x31e/0xec0
[    6.257680]  iscsi_sw_tcp_recv+0x12f/0x390
[    6.258061]  __tcp_read_sock+0x1ab/0x810
[    6.258853]  iscsi_sw_tcp_data_ready+0x18b/0x510
[    6.259808]  tcp_data_queue+0x1f13/0x4cd0
[    6.260567]  tcp_rcv_established+0x8a5/0x3a00
[    6.261931]  tcp_v4_do_rcv+0x449/0x960
[    6.262269]  tcp_v4_rcv+0x2245/0x3bc0

Fixes: 8afa143 ("[SCSI] libiscsi: handle immediate command rejections")
Cc: stable@vger.kernel.org
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Yehyeong Lee <yhlee@isslab.korea.ac.kr>
Link: https://patch.msgid.link/20261007015842.634893-3-yhlee@isslab.korea.ac.kr
Signed-off-by: Martin K. Petersen (Oracle) <mkp@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/scsi/libiscsi.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=7215a69b6456fda79c0935c2959045dff3fcaac8

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

The original Linux kernel CVE announcement for CVE-2026-99153 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99153

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:N/I:H/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: unknown
  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).