[CVE-2026-90303][MODERATE 7.0] ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faults [ Upstream

[CVE-2026-90303][MODERATE 7.0] ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faults [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90303
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faults [ Upstream
Commit: ab14f07952adfe735d86a53518f8cd576dfd5892
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ab14f07952adfe735d86a53518f8cd576dfd5892
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90303
Analysis date: Fri, 18 Sep 2026 09:36:00 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90303 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90303

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-2026-90303	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90303 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A race in the ARM user fault debug path can let show_pte traverse page table pages without holding the mmap lock while another thread in the same process removes mappings with munmap. This creates a use after free candidate in page table traversal and can cause a kernel panic, especially on ARM LPAE when PMD page table pages are freed during show_pte. For the CVSS the PR:L is used because a local user process can trigger user faults and concurrent mapping changes, but reliable triggering requires the affected debug configuration and a race window. The issue is not network reachable and requires local code execution on the target. Impact is at least local denial of service via kernel crash. In the paranoid score, limited confidentiality or integrity impact is kept for manual review because the bug is a UAF in page table traversal and the patch also avoids dumping kernel space addresses for user faults.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	READ OOB DEADLOCK DANGER UAF HARDWARE KPANIC MEMORY 	NO	NO	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 4
* Applied conservative floor: REAL UAF FLOOR 4 changed 3 -> 4
* Applied paranoid floor: REAL UAF FLOOR 4 changed 3 -> 4
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Positive signals:

* +2 Real UAF / active lifetime violation. The commit directly states that show_pte() may traverse page table pages while another thread frees them via munmap(), causing use-after-free.
* +1 Reliable kernel crash / strong DoS. The commit states that CONFIG_ARM_LPAE can panic if PMD page table pages are freed while show_pte() is running.
* +1 Local unprivileged trigger. A local user process can create user faults and concurrently modify its own mappings with munmap() under the affected debug configuration.

Negative signals:

* -1 Non-default debug / boot-time exposure. The vulnerable user-fault path requires CONFIG_DEBUG_USER=y and the boot command line user_debug=31, which is a concrete special debug configuration prerequisite.

Non-awarded material signals:

* Controlled reclaim not demonstrated. The patch does not show attacker-shaped replacement of freed page-table pages.
* Arbitrary write not demonstrated. The stale operation is page-table traversal and diagnostic dumping, not an attacker-directed write.
* Confidentiality impact not awarded. The patch mentions possible security implications from dumping kernel-space addresses for user faults, but the supplied evidence does not establish attacker-readable disclosure.
* Integrity impact not awarded. No modification of protected state or attacker-controlled corruption sink is established.
* Structured stale-object leverage not awarded. Page table pages are active kernel structures, but the stale use shown is diagnostic traversal leading to crash, not reuse of attacker-controlled fields for a useful primitive.
* Weak LPE not awarded. UAF alone is insufficient without reclaim, object replacement, directed corruption, callback influence, or another concrete leverage mechanism.
* Extra availability point not awarded. The panic/crash is already counted once as strong DoS.
* Race penalty not awarded. Although this is a race, the same local process can repeatedly drive user faults and mapping changes, so the race is not treated as a separate hard one-shot timing penalty.

Repeated release/refcount analysis:

* First release can end lifetime: not applicable. The freed objects are page table pages released by munmap(), not a visible put/release on the exact same reference in this patch.
* Exact same reference survives: not in the repeated-refcount sense.
* Second operation is a real lifetime/refcount mutation: no.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no. The case lacks concrete repeated lifetime mutation, controlled reclaim, or meaningful stale structured processing beyond diagnostic traversal.

3. Reachability analysis

The evaluated attacker is an ordinary local user on an affected ARM system. The user can trigger user-mode faults and can concurrently call munmap() from another thread in the same process. No host-admin-equivalent privilege is needed for the runtime trigger once the affected configuration is present.

There is prior privileged setup in practice because CONFIG_DEBUG_USER=y must be built in and user_debug=31 must be supplied on the kernel command line. That is accounted for as a non-default debug exposure penalty, not as HostAdminRequired=YES for the attacker.

The issue is not network reachable. It is not namespace-scoped. No CAP_NET_ADMIN, BPF, KVM, device assignment, or special userspace control-plane capability is involved. CONFIG_ARM_LPAE affects whether the demonstrated impact reaches kernel panic, but the lifetime bug itself is in the ARM user-fault debug path.

Race repeatability is moderate. The race requires overlap between show_pte() traversal and munmap() freeing page-table pages, but both sides are locally triggerable and repeatable by the same process.

4. Primitive and severity interpretation

The exact primitive is a use-after-free during show_pte() page-table traversal. The stale storage consists of page table pages freed by concurrent munmap() while the debug fault path still walks them without mmap locking.

This is an active kernel data-structure lifetime violation, but the stale use shown by the patch is diagnostic traversal in a fault path. It is not a concrete repeated release/refcount mutation, not an arbitrary write, and not a controlled reclaim primitive.

PrimitiveClass=CLASS_B because a real kernel UAF is established. It remains constrained because the demonstrated consequence is kernel crash/panic under a debug configuration, and no useful post-free exploitation primitive is established.

The demonstrated consequence is local denial of service via kernel panic. The speculative consequence is limited information exposure or broader corruption if freed page-table memory is reused in a useful way, but that is not established by the supplied patch.

ImportantCandidate=NO because the evidence supports a constrained crash-oriented UAF rather than strong unresolved exploitation leverage. ManualReview=RECOMMENDED because this is still a real page-table lifetime UAF and should not be dismissed as a harmless warning. AutoDowngradeAllowed=YES because no controlled corruption, authorization bypass, repeated lifetime mutation, COW violation, or concrete LPE path is established.

Likely operational severity is Borderline / Moderate: meaningful for affected debug ARM systems, but not an Important-class candidate from the supplied evidence alone.

5. One-sentence report phrase

A local race in the ARM user fault debug path can let show_pte() traverse page table pages after concurrent munmap() has freed them, causing a use-after-free and possible kernel panic under CONFIG_DEBUG_USER with user_debug=31.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a real UAF in page-table traversal, but the currently supported impact is local DoS under a non-default debug configuration without demonstrated reclaim, arbitrary write, information disclosure, or privilege escalation.

7. Call-site confidence

Call-site confidence: high

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

Patch: ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faults [ Upstream
Commit: ab14f07952adfe735d86a53518f8cd576dfd5892
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ab14f07952adfe735d86a53518f8cd576dfd5892

Changed files:
  arch/arm/mm/fault.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=ab14f07952adfe735d86a53518f8cd576dfd5892

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

The original Linux kernel CVE announcement for CVE-2026-90303 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90303

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:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 4

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).