* [CVE-2026-98400][LOW] s390/ipl: Fix NULL deref in kdump without re-IPL parm block [ Upstream
@ 2026-10-15 3:28 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-15 3:28 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98400
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: s390/ipl: Fix NULL deref in kdump without re-IPL parm block [ Upstream
Commit: 030e88812435fc5d6aa42eee41fa77b5ea620327
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=030e88812435fc5d6aa42eee41fa77b5ea620327
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98400
Analysis date: Wed, 14 Oct 2026 23:28:50 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98400 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98400
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: LOW
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98400 LOW https://www.kernelcve.org/list/?q=CVE-2026-98400 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=0 LEGACY=LOW RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both LOW) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.1';DESCR 'A NULL pointer dereference can occur in the s390 kdump shutdown path when the system was booted without a re IPL parameter block and reipl_block_actual remains NULL. The failure occurs after the kernel has already entered machine_crash_shutdown and can prevent successful crash dump collection or the expected reboot, potentially leaving the machine unavailable until external recovery. For the CVSS the PR:H reflects that reliable direct triggering normally requires administrative control over kdump or a privileged method of forcing a kernel crash. The issue is not directly network reachable and is limited to s390 systems using kdump with boot methods such as HMC FTP boot or QEMU direct kernel boot. The demonstrated impact is availability loss in the crash recovery path, with no supported UAF, controlled memory write, information disclosure, or privilege escalation primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.1 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 2.1 and ActionableScore 0 with primitive class CLASS_C and manual review NO. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) MAYBE OOB INIT SIMPLEFIX HARDWARE DEBUGFS LINUS BOOT - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: -2.
* Conservative score: 0. The negative raw result is normalized to the minimum score of 0.
* Raw paranoid score: -2.
* Paranoid score: 0. The negative raw result is normalized to the minimum score of 0.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Reliable crash-recovery disruption. The NULL dereference occurs in `machine_crash_shutdown()` and can prevent kdump collection or the expected reboot, leaving the machine dependent on external recovery.
* -2 Proven host-administrator-equivalent requirement. Direct triggering requires control over the boot and kdump configuration plus a privileged way to force the kernel into its crash-shutdown path.
* -1 Rare and difficult-to-reach configuration. The defect is restricted to s390, requires kdump, and requires an IPL method that leaves `reipl_block_actual` unset, such as HMC FTP boot or QEMU direct kernel boot.
* No memory-corruption point. The established operation is a NULL-based read of `reipl_block_actual->hdr.len`, not a UAF, OOB write, arbitrary write, or lifetime violation.
* No extra Availability point. Failure of dump collection and reboot is the same crash-recovery consequence already counted.
* No confidentiality or integrity points. No disclosure, attacker-controlled write, protected-state modification, or authorization bypass is established.
* No B5-R signal. There is no retry-accumulated heap OOB write or later consumption of corrupted structured state.
* No B3-PENDING signal. No shared-backing or file-backed write exists.
* No B4-PENDING signal. The added NULL check is a validity check, not a mandatory authorization guard changing DENY to ALLOW.
* Remote reachability, controlled payload, controlled target, privilege escalation, and practical exploitation leverage are not established.
3. Reachability analysis
The vulnerable call occurs after the system has entered `machine_crash_shutdown()`. A direct standalone trigger therefore requires administrative control sufficient to configure kdump or the relevant boot environment and deliberately initiate a crash. Numeric host UID 0 is not explicitly established as mandatory because equivalent administrative mechanisms may initiate the operation, so `RequiresHostUID0` remains UNKNOWN while effective host-administrator privilege is established.
The complete operation is not namespace scoped. No ordinary-user, delegated-capability, or network-triggered path is shown. An attacker who can independently panic the kernel through another vulnerability might cause this recovery defect to appear afterward, but that unrelated primary vulnerability is not part of this patches trigger model. The prerequisites are s390, kdump, and a boot mode that provides no re-IPL parameter block. There is no race or retry mechanism.
4. Primitive and severity interpretation
The exact primitive is an invalid NULL-based read in `set_os_info_reipl_block()`. When `reipl_block_actual` is NULL, the function passes that pointer to `os_info_entry_add_data()` and reads `reipl_block_actual->hdr.len`. Depending on the s390 lowcore mapping, this may fault or may read accessible address-zero data and create an empty entry that the dump kernel ignores.
This is CLASS_C invalid-state and crash-recovery behavior. It is not an active structured UAF, fixed stale storage UAF, repeated release, refcount mutation, authorization bypass, or heap corruption primitive. The demonstrated consequence is failed or unreliable kdump and reboot processing after the kernel is already crashing. Stronger consequences such as disclosure, privilege escalation, arbitrary modification, or code execution are unsupported.
`ImportantCandidate=NO` because no independently useful corruption or security-boundary primitive remains after excluding the recovery failure. `AutoDowngradeAllowed=YES` because the issue is architecture-specific, administrator-triggered, and limited to crash recovery.
5. One-sentence report phrase
An s390 system booted without a re IPL parameter block can dereference a NULL pointer during kdump shutdown, potentially preventing crash dump collection and the expected reboot, but the path requires administrative crash control and provides no demonstrated corruption or privilege escalation primitive.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch fixes a direct NULL check omission in an administrator-controlled, architecture-specific crash-recovery path, with no UAF, write primitive, authorization bypass, or unresolved Important-grade leverage.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: s390/ipl: Fix NULL deref in kdump without re-IPL parm block [ Upstream
Commit: 030e88812435fc5d6aa42eee41fa77b5ea620327
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=030e88812435fc5d6aa42eee41fa77b5ea620327
Changed files:
arch/s390/kernel/ipl.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=030e88812435fc5d6aa42eee41fa77b5ea620327
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98400 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98400
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:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.1
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: unknown
Paranoid ActionableScore: 0
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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