[CVE-2026-89962][MODERATE REGULAR] powerpc/kexec_file: Prevent kexec range truncation

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

CVE: CVE-2026-89962
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: powerpc/kexec_file: Prevent kexec range truncation
Commit: 9ef63622e6cee588ea4b763a6afc87065254b36a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9ef63622e6cee588ea4b763a6afc87065254b36a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89962
Analysis date: Wed, 16 Sep 2026 09:26:11 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89962 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89962

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 REGULAR
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-2026-89962	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89962 CHECK WITH IMPACT FROM ORIG NN 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:L/I:H/A:H';CWE-682;CWE-693;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:H/A:H';BEST CVSS score: '6';DESCR 'powerpc kexec_file memory range merging can truncate a larger active merged range when later overlapping ranges are fully contained inside it. This can remove valid memory fragments from the kexec or crash kernel exclude lists and may allow the crash kernel to overwrite memory that should have been preserved. For the CVSS the PR:H is used because reliable triggering normally requires local administrative control over kexec_file_load or crash kernel configuration, typically CAP_SYS_BOOT. The issue is not network reachable and depends on a specific overlapping memory range layout on affected powerpc systems. Impact is at least denial of service and data corruption during kexec or crash dump handling. In the paranoid view, limited confidentiality impact is kept possible because active memory corruption can affect crash dump integrity and preserved memory contents, but the patch does not show a direct arbitrary read or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	OOB DANGER KERNEL_PANIC_PLUS_UAF HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	NO	NO	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::

No UAF floor or corruption floor was applied. The paranoid score adds one defensible point for the security relevance of corrupted kexec crash-kernel memory exclusion boundaries, but does not promote the issue to Important because triggering is host-admin-equivalent and no below-admin security boundary bypass is established.

2. Signal breakdown

Conservative positive signals:

* +1 Weak / indirect corruption candidate. The merge logic can truncate exclude ranges, causing the crash kernel memory map to omit regions that should remain protected.
* +1 Reliable crash / strong DoS. The supplied text directly states that the crash kernel may overwrite active memory, causing data corruption or crashes.
* +1 Memory layout / range invariant restoration. The patch restores consistency between sorted range boundaries and the active merged range by comparing against idx and using max().

Conservative negative signals:

* -2 Host-admin-equivalent requirement. Reliable triggering normally requires kexec_file_load or crash-kernel configuration control, which is CAP_SYS_BOOT or root-equivalent on the host.

Paranoid additional signal:

* +1 Privileged kernel memory-boundary corruption concern. The affected data controls kexec or crash-kernel exclusion boundaries, and an incorrect boundary can expose active memory to overwrite during kexec or crash dump handling.

Important non-awarded signals:

* No Real UAF is established.
* No repeated release or refcount mutation exists.
* No controlled reclaim is demonstrated.
* No arbitrary or directed kernel write by a below-admin attacker is demonstrated.
* No local unprivileged trigger is established.
* No network reachability is established.
* No confidentiality bonus is awarded because there is no concrete disclosure path.
* No LPE or security-boundary bypass is established. A host administrator capable of kexec already has broad control over the kernel.

3. Reachability analysis

The vulnerable path is in powerpc kexec_file memory range processing. The practical trigger requires control over kexec or crash-kernel setup and a memory range layout where one larger range fully contains later smaller ranges. That operation is normally host-admin-equivalent and governed by CAP_SYS_BOOT or root-level system configuration.

This is not namespace-scoped. There is no evidence that an attacker can perform the complete kexec_file or crash-kernel configuration flow inside an attacker-created namespace. There is no direct network trigger. There is no special external hardware requirement beyond affected powerpc kexec or kdump usage, but the feature itself is an administrative kernel transition path.

Race repeatability is not relevant. This is a deterministic logic bug in range merging, not a timing race.

4. Primitive and severity interpretation

The exact primitive is incorrect merging of overlapping memory ranges. The bug can shrink an active merged range and drop valid fragments from the kexec exclude list. The demonstrated consequence is that a crash kernel may overwrite memory that should have been excluded, leading to data corruption or crashes.

This is not an active structured UAF, not fixed stale storage, and not a repeated lifetime mutation. It is best classified as CLASS_C because the demonstrated behavior is invalid security-relevant state and crash or corruption during an admin-controlled kexec path, without an independently useful exploitation primitive for a lower-privileged attacker.

ImportantCandidate=NO because no below-host-admin reachability, controlled corruption primitive, privilege escalation, or authorization bypass is established. ManualReview=RECOMMENDED because the bug affects memory exclusion boundaries and crash-kernel overwrite behavior, which is more security-relevant than a harmless bookkeeping bug. AutoDowngradeAllowed=YES because the remaining evidence supports admin-gated DoS/data-corruption behavior rather than an unresolved Important-grade primitive.

Likely operational severity is ordinary to borderline Moderate for kernel-security triage, despite a higher paranoid CVSS-like interpretation.

5. One-sentence report phrase

A logic error in powerpc kexec_file range merging can truncate kexec exclude ranges and may allow a crash kernel to overwrite active memory, causing data corruption or DoS, but reliable triggering appears to require host-admin-equivalent kexec or crash-kernel control.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the bug affects crash-kernel memory exclusion boundaries and can lead to active memory overwrite, but the supplied evidence indicates host-admin-equivalent reachability and does not establish a lower-privilege exploitation path.

7. Call-site confidence

Call-site confidence: medium

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

Patch: powerpc/kexec_file: Prevent kexec range truncation
Commit: 9ef63622e6cee588ea4b763a6afc87065254b36a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9ef63622e6cee588ea4b763a6afc87065254b36a

Commit description:

Sashiko AI review pointed out the following issue.

The __merge_memory_ranges() function incorrectly handles overlapping
memory ranges when merging them. Although sort_memory_ranges() sorts all
ranges by their start address in ascending order beforehand, the merge
logic remains defective in two ways:

1. It compares the current range's start against the previous element (i-1)
   instead of the running target index (idx)

2. It unconditionally overwrites 'ranges[idx].end' with 'ranges[i].end'.

This logic flaw leads to critical memory truncation when a larger memory
range completely subsumes subsequent smaller ranges.

For example, consider a sorted input array with three ranges:
  Range A (idx=0): [0x1000 - 0x9000]
  Range B (i=1):   [0x2000 - 0x5000] (completely inside Range A)
  Range C (i=2):   [0x6000 - 0x8000] (completely inside Range A)

1. When i=1 (Range B):
   ranges[1].start (0x2000) <= ranges[0].end + 1 (0x9001) is TRUE.
   The code executes: ranges[0].end = ranges[1].end, which erroneously
   shrinks Range A's end from 0x9000 down to 0x5000.

2. When i=2 (Range C):
   ranges[2].start (0x6000) <= ranges[1].end + 1 (0x5001) is FALSE.
   The code falls into the else block, creating a broken new range.

As a result, valid memory fragments [0x5001 - 0x5fff] and [0x8001 - 0x9000]
are completely lost from the kexec exclude lists, potentially allowing
the crash kernel to overwrite active memory, causing data corruption
or crashes.

Fix this by ensuring the start of the current range is compared against the
end of the active merged range (idx), and use max() to safely prevent the
outer boundary from being truncated.

Cc: stable@vger.kernel.org
Fixes: 180adfc ("powerpc/kexec_file: Add helper functions for getting memory ranges")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260729012948.2797865-4-ruanjinjie@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/powerpc/kexec/ranges.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=9ef63622e6cee588ea4b763a6afc87065254b36a

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

The original Linux kernel CVE announcement for CVE-2026-89962 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89962

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:H/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:H/A:H
  The Best / paranoid CVSS score: 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: 2
  Paranoid ActionableScore: 3

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).