[CVE-2026-53354][MODERATE 7.0] arm64: errata: Mitigate TLBI errata on various Arm CPUs

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

CVE: CVE-2026-53354
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: arm64: errata: Mitigate TLBI errata on various Arm CPUs
Commit: 925058203229403008d77a52b1e63e2ae5f4a3cf
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=925058203229403008d77a52b1e63e2ae5f4a3cf
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53354
Analysis date: Wed, 01 Jul 2026 10:20:23 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
CVE-2025-10263 is an Arm CPU TLBI completion erratum where writes translated by invalidated TLB entries may not be globally observed after TLBI/DSB, creating a local timing-dependent stale memory ordering risk with possible DoS and paranoid UAF-like integrity impact on affected arm64 systems.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53354 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53354

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-53354	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;CWE-693;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'CVE-2025-10263 affects several Arm Cortex, Neoverse, and C1 CPUs where a broadcast TLBI/DSB sequence may complete before affected memory writes are globally observed. This can break the kernel assumption that writes translated by an invalidated TLB entry are complete after the barrier, creating a stale translation memory ordering risk around unmap, page table changes, and page reuse. For the CVSS the PR:L is chosen because practical triggering requires local code execution on an affected arm64 system, for example through memory management activity such as mmap, munmap, mprotect, fork, or exit. The issue is not directly network reachable. Impact is at least local denial of service or memory consistency failure, and in the paranoid case may allow confidentiality or integrity impact due to UAF-like stale write behavior after invalidated translations. AC:H is used because reliable exploitation depends on hardware timing, affected CPU models, and a narrow TLBI related race window.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	HARDWARE  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  Local user activity can plausibly exercise TLBI paths through memory-management operations such as mmap, munmap, mprotect, fork, exit, and page-table teardown.
* Memory corruption, weak/indirect corruption candidate: +1
  The bug is a hardware memory-ordering erratum, not a direct C-code UAF, but stale write completion after invalidated translations can plausibly corrupt memory after page-table changes or page reuse.
* Real lifetime or ownership corruption concern: +1
  The relevant risk is that writes translated by an invalidated TLB entry may complete after the kernel believes the mapping is gone, creating a stale-ownership style hazard.
* Broad/default/common subsystem exposure: +1
  TLBI and page-table invalidation are core arm64 MM operations, and the affected CPU list includes many Cortex, Neoverse, and C1 cores.
* Hard or timing-dependent condition: -1
  Reliable exploitation depends on affected hardware behavior, TLBI timing, memory ordering, and page reuse windows.
* Availability impact realistic: +1
  Memory consistency failures in core MM paths can realistically lead to crashes or system instability, though a concrete crash primitive is not shown in the patch.

Conservative total: 4

Paranoid additional signals:

* Weak LPE concern: +1
  A stale write after unmap or page reuse may theoretically affect memory now owned by another object or privilege domain, but no controlled reclaim or write primitive is demonstrated.
* Confidentiality impact plausible: +1
  If stale memory effects cross ownership boundaries, limited disclosure or observation of inconsistent state is plausible, but not directly proven.
* Integrity impact plausible: +1
  The strongest concern is integrity impact from delayed writes landing after page ownership or mapping state has changed.

Paranoid total: 7

## 3. Reachability analysis

The issue is not network reachable by itself. Triggering requires execution on an affected arm64 CPU and activity that drives kernel TLB invalidation paths. A local unprivileged process can plausibly create such activity through normal memory-management syscalls, but reliable exploitation would require difficult timing and affected hardware.

Namespaces and containers do not remove the concern because container workloads still exercise host kernel MM and TLBI paths. However, the bug is hardware-dependent and only applies to listed Arm CPU families when the mitigation is absent.

The affected path is core architecture MM behavior, not a niche driver path. The workaround is enabled through ARM64_WORKAROUND_REPEAT_TLBI for affected MIDR ranges.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup issue. It is a hardware erratum affecting core memory-management ordering. The patch does not show a direct arbitrary write, attacker-controlled reclaim, function-pointer overwrite, or demonstrated LPE chain, so the conservative score should not assume full exploitation.

The theoretical risk is higher than a simple DoS because stale writes after invalidated translations can resemble UAF-like page ownership corruption around unmap and page reuse. Realistic exploitation evidence is limited and timing-dependent, but the primitive class is serious enough to avoid auto-closing.

This should be treated as Actionable Moderate at minimum, with Strong Important candidate handling for affected arm64 platforms.

## 5. One-sentence report phrase

CVE-2025-10263 is an Arm CPU TLBI completion erratum where writes translated by invalidated TLB entries may not be globally observed after TLBI/DSB, creating a local timing-dependent stale memory ordering risk with possible DoS and paranoid UAF-like integrity impact on affected arm64 systems.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a core arm64 MM hardware erratum with possible stale write and page ownership implications. The patch does not prove a practical LPE primitive, but the affected path is fundamental enough that affected products should receive manual platform and exposure review.

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UPSTREAM PATCH SUMMARY
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Patch: arm64: errata: Mitigate TLBI errata on various Arm CPUs
Commit: 925058203229403008d77a52b1e63e2ae5f4a3cf
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=925058203229403008d77a52b1e63e2ae5f4a3cf

Commit description:

A number of CPUs developed by Arm suffer from errata whereby a broadcast
TLBI;DSB sequence may complete before the global observation of writes
which are translated by an affected TLB entry.

These errata ONLY affect the completion of memory accesses which have
been translated by an invalidated TLB entry, and these errata DO NOT
affect the actual invalidation of TLB entries. TLB entries are removed
correctly.

This issue has been assigned CVE ID CVE-2025-10263 .

To mitigate this issue, Arm recommends that software follows any
affected TLBI;DSB sequence with an additional TLBI;DSB, which will
ensure that all memory write effects affected by the first TLBI have
been globally observed. The additional TLBI can use any operation that
is broadcast to affected CPUs, and the additional DSB can use any option
that is sufficient to complete the additional TLBI.

The ARM64_WORKAROUND_REPEAT_TLBI workaround is sufficient to mitigate
the issue. Enable this workaround for affected CPUs, and update the
silicon errata documentation accordingly.

Note that due to the manner in which Arm develops IP and tracks errata,
some CPUs share a common erratum number.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
[Mark: backport to v5.10.y]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/arm64/kernel/cpu_errata.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=925058203229403008d77a52b1e63e2ae5f4a3cf

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

The original Linux kernel CVE announcement for CVE-2026-53354 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53354

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 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: 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).