[CVE-2026-90011][MODERATE 7.0] scsi: target: iscsi: Reserve a terminator byte for the login payload

[CVE-2026-90011][MODERATE 7.0] scsi: target: iscsi: Reserve a terminator byte for the login payload

[AL-KERNEL]

CVE: CVE-2026-90011
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: scsi: target: iscsi: Reserve a terminator byte for the login payload
Commit: 5fac79f248c37774d1dd761406f83d25ca6ff8e4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5fac79f248c37774d1dd761406f83d25ca6ff8e4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90011
Analysis date: Wed, 16 Sep 2026 15:21:34 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90011 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90011

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-2026-90011	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90011 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:L/I:L/A:H';CWE-126;CWE-170;*CWE-20;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.6';DESCR 'An out-of-bounds read in the iSCSI target login path can occur because login req_buf is allocated with exactly MAX_KEY_VALUE_PAIRS bytes and a maximum sized login payload leaves no byte for a NUL terminator. The buffer is later consumed as a C string by CHAP login parsing paths such as chap_check_algorithm and extract_param, so strlen and strstr style operations can walk past the end of the allocation into adjacent slab memory. A remote unauthenticated initiator can trigger this against an iSCSI target portal configured for CHAP by sending a login PDU with a near maximum DataSegmentLength. For the CVSS the PR:N is selected because the trigger occurs before successful authentication and only requires network reachability to the target portal. Impact is at least remote denial of service via kernel crash. For the paranoid score, limited confidentiality or integrity impact is kept because this is a network reachable pre-auth OOB read in authentication string parsing, but HHH is not selected because the patch does not show an out-of-bounds write or arbitrary write primitive. iSCSI targets are usually deployed in storage or data center networks rather than exposed to the public Internet, so practical exploitation usually requires access to a local or trusted storage network.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5)	YES	LOG LINUS TEST  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4. No floor or cap applied.
* Raw paranoid score: 5
* Paranoid score: 5. No floor or cap applied.
* Final recommended bucket: **Actionable Moderate**::

2. Signal breakdown

Conservative signals:

* +2 Remote reachable / directly network-triggerable: an unauthenticated iSCSI initiator can reach the vulnerable login parsing path when the target portal is configured for CHAP.
* +1 Weak memory-safety primitive: the login payload can fill the whole req_buf allocation without leaving a NUL terminator, and later C-string operations can read past the end of the object.
* +1 Reliable kernel crash / strong DoS: strlen, strstr, kstrdup style parsing over an unterminated kernel buffer can walk into adjacent slab memory and plausibly fault or crash the kernel.

Paranoid additional signal:

* +1 Memory layout invariant restoration: the patch restores the allocation-size versus maximum-copy-size versus C-string-terminator invariant by reserving one extra zeroed byte. This supports treating the issue as an actionable remote pre-auth memory-safety bug rather than ordinary input rejection.

Non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Real UAF not demonstrated.
* Confidentiality point not awarded because no concrete user-visible or network-visible disclosure path is established.
* Integrity point not awarded because the patch does not establish an authorization bypass, OOB write, or attacker-controlled modification of protected state.
* Extra Availability point not awarded because the same crash/DoS is already counted once.
* ImportantCandidate is not set because the established primitive is OOB read / crash risk, not Class A corruption or strong Class B lifetime corruption.

3. Reachability analysis

The trigger is remote and pre-authentication for an exposed iSCSI target portal configured for CHAP. The attacker does not need a local account or host-admin privilege on the victim, so HostAdminRequired=NO. Namespace-scoped privilege is not relevant to the complete trigger path, so NamespaceScopedPrivilege=NO.

There is a configuration prerequisite: the iSCSI target service must be enabled and reachable, and the affected CHAP login path must be used. This is not a reason to subtract a score point because the vulnerable service is the network-facing attack surface itself. In practice, iSCSI targets are usually deployed on storage or data-center networks rather than the public Internet, but exposure to an untrusted storage network is sufficient for exploitation.

No race, special hardware, local control-plane action, or prior attacker-controlled host setup is required beyond network reachability to the configured target portal.

4. Primitive and severity interpretation

The exact primitive is a remote pre-authentication out-of-bounds read caused by using a maximum-sized login payload as an unterminated C string. The write into req_buf remains in bounds, but the later parsing path may read beyond the allocation into adjacent slab memory.

This is not an active structured UAF and not fixed stale storage. It is a bounded allocation/terminator bug leading to lengthless string traversal. There is no concrete repeated release/refcount operation.

PrimitiveClass=CLASS_C because the demonstrated consequence is primarily crash/DoS and invalid memory read behavior without an independently useful corruption, write, disclosure, or privilege-escalation primitive. The operational severity is Actionable Moderate because the bug is remote, unauthenticated, pre-auth, and in kernel storage-target authentication parsing.

AutoDowngradeAllowed=NO because automatically closing a remote pre-auth kernel memory-safety issue would risk losing a meaningful review target, even though the evidence does not currently justify Important-class scoring.

5. One-sentence report phrase

A remote unauthenticated initiator can send a near maximum sized CHAP login payload to an iSCSI target so that the kernel parses an unterminated login buffer as a C string, causing an out-of-bounds read and possible kernel crash.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Remote pre-auth kernel memory-safety issues in authentication parsing should be reviewed manually, even when the currently established impact is DoS and limited OOB read rather than proven disclosure or privilege escalation.

7. Call-site confidence

Call-site confidence: high

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

Patch: scsi: target: iscsi: Reserve a terminator byte for the login payload
Commit: 5fac79f248c37774d1dd761406f83d25ca6ff8e4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5fac79f248c37774d1dd761406f83d25ca6ff8e4

Commit description:

iscsi_target_check_login_request() rejects a login PDU whose
DataSegmentLength exceeds MAX_KEY_VALUE_PAIRS, but the test is '>' and
login->req_buf is allocated with exactly MAX_KEY_VALUE_PAIRS
bytes. Since iscsit_get_login_rx() receives payload_length + padding
bytes, where

	padding = ((-payload_length) & 3);

any payload_length from 8189 to 8192 fills the whole 8192 byte
buffer. The write stays in bounds, but no byte is left for a NUL
terminator.

The buffer is subsequently consumed as a C string. In the CHAP path
chap_check_algorithm() calls kstrdup(a_str), and extract_param() calls
strstr(in_buf, pattern) followed by strlen_semi(), none of which take a
length. convert_null_to_semi() additionally rewrites every embedded NUL
to ';', so even a payload made of well formed NUL separated key=value
records is left without a terminator. These walk past the end of the
object into adjacent slab memory. It is reachable by an unauthenticated
initiator against a portal configured for CHAP; when authentication is
not required iscsi_login_zero_tsih_s2() rewrites AuthMethod to None and
the CHAP path is never entered.

Allocate one extra byte. kzalloc() zeroes it and nothing ever writes to
it, as every writer copies to offset 0 for at most MAX_KEY_VALUE_PAIRS
bytes, so the buffer is always terminated.

Fixes: e48354c ("iscsi-target: Add iSCSI fabric support for target v4.1")
Assisted-by: Claude Opus5 (custom harness)
Cc: stable@vger.kernel.org
Signed-off-by: Sujal Tuladhar <sujaltuladhar1231@gmail.com>
Signed-off-by: Martin K. Petersen (Oracle) <mkp@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/target/iscsi/iscsi_target_login.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=5fac79f248c37774d1dd761406f83d25ca6ff8e4

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

The original Linux kernel CVE announcement for CVE-2026-90011 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90011

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:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 8.6

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: 4
  Paranoid ActionableScore: 5

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).