[CVE-2026-53067][MODERATE 7.0] PCI: endpoint: pci-ep-msi: Fix error unwind and prevent double alloc [ Upstream

[CVE-2026-53067][MODERATE 7.0] PCI: endpoint: pci-ep-msi: Fix error unwind and prevent double alloc [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53067
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: PCI: endpoint: pci-ep-msi: Fix error unwind and prevent double alloc [ Upstream
Commit: 175717cfc06cab79f84cd037d66dda1b8564cd9e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=175717cfc06cab79f84cd037d66dda1b8564cd9e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53067
Analysis date: Fri, 26 Jun 2026 10:41:39 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A PCI endpoint MSI doorbell allocation failure can leave `epf->db_msg` pointing to freed memory, allowing later cleanup or retry paths to trigger a double free or use after free and cause at least a local kernel DoS, with limited but nonzero security concern under delegated device-management scenarios.

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

The original Linux kernel CVE announcement for CVE-2026-53067 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53067

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-2026-53067	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-415;*CWE-416;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'PCI endpoint doorbell allocation can leave epf db_msg pointing to freed memory when MSI vector allocation fails after the message array was stored in EPF state. Later cleanup or retry paths may operate on the stale pointer, creating a double free or use after free condition in kernel memory and causing at least a local DoS. For the CVSS the PR:L is used in the paranoid score because some systems may delegate PCI endpoint function setup to service accounts or constrained administration contexts, even though the default setup is usually root or CAP_SYS_ADMIN. The issue is not network reachable and depends on PCI endpoint framework usage and an MSI allocation failure path. Impact is at least kernel crash and, because the primitive is a dangling pointer with possible double free, worst case confidentiality and integrity impact should be manually reviewed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-53067  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	LEAK UAF LINUS  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Paranoid score signals:

* Generic memory corruption: +2. The patch fixes a stale freed pointer in `epf->db_msg`, which can lead to double free or use after free.
* Real lifetime corruption: +1. The failure path frees `msg` but previously left EPF state pointing to freed memory.
* Reliable kernel crash / strong DoS: +1. Later cleanup or retry can operate on the stale pointer and crash the kernel.
* Privileged kernel/device-management memory corruption path: +1. The bug is in PCI endpoint MSI doorbell allocation, a trusted device-management path.
* Weak LPE concern: +1. Double free or UAF in kernel memory can be security relevant, but the patch does not show a controlled reclaim, arbitrary write, or reliable object-confusion primitive.
* Requires MSI allocation failure / special error path: -1. Triggering requires the allocation to fail after `epf->db_msg` has been populated.
* Constrained primitive / no clear attacker-controlled payload: -1. The freed object and overwrite conditions appear constrained by driver state rather than attacker-chosen data.
* Rare and configuration-dependent subsystem: -1. PCI endpoint framework and RC-to-EP doorbell support are not broad default attack surfaces.
* Confidentiality impact plausible: +1. In the paranoid view, kernel UAF or double free can potentially expose or corrupt adjacent kernel objects.
* Integrity impact plausible: +1. In the paranoid view, double free or UAF may become more than DoS depending on allocator behavior and reachable retry or cleanup paths.

Conservative score is lower because typical triggering requires privileged PCI endpoint configuration and a specific MSI allocation failure path, with no demonstrated controlled corruption primitive.

## 3. Reachability analysis

The bug is local and not network reachable. In typical deployments, PCI endpoint configuration and endpoint function setup require root or equivalent administrative privileges, so the conservative interpretation applies a strong privilege limitation. A paranoid interpretation uses reduced-privilege or delegated-device-management scenarios, where a service account, containerized root, or constrained admin component may be able to exercise endpoint setup without full host-root equivalence.

The path is not default-exposed on ordinary servers or desktops. It depends on PCI endpoint framework usage, platform MSI support, RC-to-EP doorbell support, and a failure in MSI vector allocation. Realistic exploitation is therefore configuration-dependent, but the underlying bug class is kernel lifetime corruption rather than a pure logic or warning-only issue.

## 4. Severity interpretation

This is not an ordinary resource leak or harmless unwind bug. It leaves a kernel structure pointing to freed memory and can later cause double free or use after free. Realistically, the most likely impact is local kernel crash during cleanup or retry after a failed allocation.

Theoretical privilege escalation is not proven by the patch. There is no demonstrated arbitrary write, controlled reclaim, or attacker-controlled object replacement. However, because the bug creates a stale kernel pointer and possible double free in a privileged device-management path, it should be treated as an actionable Moderate and manually reviewed rather than auto-closed.

## 5. One-sentence report phrase

A PCI endpoint MSI doorbell allocation failure can leave `epf->db_msg` pointing to freed memory, allowing later cleanup or retry paths to trigger a double free or use after free and cause at least a local kernel DoS, with limited but nonzero security concern under delegated device-management scenarios.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug is a real kernel lifetime corruption issue involving stale freed state and possible double free. Even though practical reachability is narrow and typical triggering is privileged, the class is security-relevant enough to require manual review.

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

Patch: PCI: endpoint: pci-ep-msi: Fix error unwind and prevent double alloc [ Upstream
Commit: 175717cfc06cab79f84cd037d66dda1b8564cd9e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=175717cfc06cab79f84cd037d66dda1b8564cd9e

Changed files:
  drivers/pci/endpoint/pci-ep-msi.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=175717cfc06cab79f84cd037d66dda1b8564cd9e

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

The original Linux kernel CVE announcement for CVE-2026-53067 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53067

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: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: 2
  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).