[CVE-2026-53047][MODERATE 7.0] efi/capsule-loader: fix incorrect sizeof in phys array reallocation [ Upstream

[CVE-2026-53047][MODERATE 7.0] efi/capsule-loader: fix incorrect sizeof in phys array reallocation [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53047
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: efi/capsule-loader: fix incorrect sizeof in phys array reallocation [ Upstream
Commit: 22022cd8851703a58f67615a17bc7e9e8682785b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=22022cd8851703a58f67615a17bc7e9e8682785b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53047
Analysis date: Thu, 25 Jun 2026 10:48:39 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An incorrect sizeof in the EFI capsule loader can underallocate the physical address array on 32 bit PAE systems, causing a constrained kernel heap overflow during capsule writes and requiring manual review despite limited deployment exposure.

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

The original Linux kernel CVE announcement for CVE-2026-53047 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53047

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
======================================================================

CVE-2026-53047	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-467;CWE-131;CWE-122;*CWE-787;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'An incorrect sizeof in the EFI capsule loader reallocation path can allocate the cap_info phys array using pointer size instead of phys_addr_t size. On 32 bit PAE systems where phys_addr_t is wider than a pointer, this can underallocate the array and later writes of physical page addresses can overflow the kernel heap. For the CVSS the PR:L is used for the paranoid case because triggering may be possible through a local firmware update path or a delegated update service rather than only by full interactive root. The issue is not network reachable and requires local access to the EFI capsule loader interface. Impact is at least local denial of service via kernel memory corruption and in the worst case may allow confidentiality or integrity impact due to a heap overflow primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4) 	MAYBE	WRITE OOB SIMPLEFIX LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Constrained kernel buffer overwrite: +1. `krealloc()` underallocates `cap_info->phys` on 32 bit PAE because `sizeof(phys_addr_t *)` is smaller than `sizeof(phys_addr_t)`.
* Privileged kernel/device-management memory corruption path: +1. The bug is in EFI capsule loading, a trusted firmware update path.
* Reliable kernel crash / strong DoS: +1. The undersized array can be overrun when physical page addresses are stored.
* Integrity impact plausible: +1. Kernel heap corruption can corrupt adjacent kernel objects, although the written values are kernel-derived physical addresses rather than arbitrary attacker bytes.
* Local/delegated trigger in paranoid interpretation: +1. Typical direct access is privileged, but firmware update helpers or delegated update services may make this closer to PR:L in practice.
* Confidentiality impact plausible in paranoid interpretation: +1. Heap corruption can theoretically affect adjacent metadata and object state, but no direct info leak is shown.
* Rare configuration: -1. The issue requires 32 bit PAE where `phys_addr_t` is 64 bit and pointers are 32 bit, plus EFI capsule loader exposure.
* Admin/root typical access in conservative interpretation: -2. Direct capsule loader use is normally restricted to root or firmware update infrastructure.

## 3. Reachability analysis

This is local, not network reachable. The affected path is the EFI capsule loader and requires writing a capsule through the firmware update interface. In typical deployments this is root-only or mediated by a privileged update service, so the conservative privilege model is admin-required. The paranoid model treats delegated firmware update paths or reduced-privilege service contexts as PR:L because the attacker may not have full host-root equivalence. The bug is architecture/configuration dependent and mainly affects 32 bit PAE systems where `phys_addr_t` exceeds pointer size.

## 4. Severity interpretation

This is not an ordinary cleanup bug because it is a real kernel heap underallocation leading to an OOB write. It is also not a clear Important by default because the overwrite payload is constrained to physical address values, target selection is not demonstrated, and affected configurations are limited. The best practical bucket is Actionable Moderate requiring manual review. A Strong Important interpretation is defensible only if a realistic adjacent-object corruption or delegated update-service trigger is confirmed.

## 5. One-sentence report phrase

An incorrect sizeof in the EFI capsule loader can underallocate the physical address array on 32 bit PAE systems, causing a constrained kernel heap overflow during capsule writes and requiring manual review despite limited deployment exposure.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Kernel heap corruption is present, even though the primitive is constrained and configuration-dependent. This should not be auto-closed without checking affected architecture support, capsule loader permissions, and whether firmware update services expose the path to reduced-privilege users.

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

Patch: efi/capsule-loader: fix incorrect sizeof in phys array reallocation [ Upstream
Commit: 22022cd8851703a58f67615a17bc7e9e8682785b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=22022cd8851703a58f67615a17bc7e9e8682785b

Changed files:
  drivers/firmware/efi/capsule-loader.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=22022cd8851703a58f67615a17bc7e9e8682785b

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

The original Linux kernel CVE announcement for CVE-2026-53047 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53047

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: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: 3
  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: NO
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).