[CVE-2026-53092][IMPORTANT] bpf: Fix linked reg delta tracking when src_reg == dst_reg [ Upstream

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

CVE: CVE-2026-53092
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: bpf: Fix linked reg delta tracking when src_reg == dst_reg [ Upstream
Commit: d88e8e4a3b52bd5b2ff3eceba4b29d1b5506d066
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d88e8e4a3b52bd5b2ff3eceba4b29d1b5506d066
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53092
Analysis date: Wed, 24 Jun 2026 12:54:31 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A BPF verifier linked-register delta tracking bug can create a verifier versus runtime mismatch when the same register is used as both source and destination, potentially allowing unsafe BPF memory access and local privilege escalation by a user with BPF loading capability.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53092 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53092

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: IMPORTANT
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-2026-53092	IMPORTANT	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-682;*CWE-20;*CWE-787;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7.8';DESCR 'For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context. This is a BPF verifier mismatch candidate, not a DoS only bug, so manual review is recommended even though reliable triggering requires local BPF loading privileges.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	WARNONLY BPF SIMPLEFIX  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Privilege escalation plausible: +2
  BPF verifier versus runtime mismatches are a historically high-risk class because incorrect verifier state can allow unsafe pointer arithmetic or bounds assumptions to reach runtime.

* Memory corruption, weak/indirect corruption candidate: +1
  The patch does not show a direct arbitrary write, UAF, or concrete overwrite primitive, but incorrect linked register delta propagation can corrupt verifier state and potentially permit invalid BPF memory access.

* Local high-control kernel data-plane API: +1
  BPF is a high-control kernel API where programs can shape verifier state, register relationships, pointer arithmetic, and memory access patterns.

* Confidentiality impact plausible: +1
  If the verifier mismatch enables out-of-bounds reads or unsafe pointer access, kernel memory disclosure is plausible.

* Integrity impact plausible: +1
  If the verifier mismatch enables out-of-bounds writes or unsafe helper/map access, kernel memory corruption or privilege escalation is plausible.

* Availability impact plausible: +1
  Invalid verifier-approved runtime behavior can plausibly crash the kernel.

* Broad/common subsystem exposure: +1
  eBPF is a common kernel subsystem, even though privileged BPF loading is restricted in many deployments.

* Requires CAP_BPF/CAP_SYS_ADMIN-like privilege in typical deployments: -2 conservative, -1 paranoid
  The code path is gated by `env->bpf_capable`, so typical triggering requires privileged BPF loading. The paranoid score reduces the penalty because CAP_BPF or similar reduced capabilities may be delegated to service accounts, container root, or sandboxed administrators that are not equivalent to full host root.

## 3. Reachability analysis

The issue is locally reachable through loading a crafted BPF program that reaches the `rX += rX` or `rX -= rX` corner case with linked register delta tracking. It is not network reachable by itself. In normal hardened deployments, unprivileged BPF is disabled and triggering requires CAP_BPF, CAP_SYS_ADMIN, or an equivalent privileged BPF loading path. Namespaces and containers matter because some environments delegate BPF-related capabilities or run reduced-privilege service accounts that are not equivalent to full host root, making the practical PR closer to PR:L in the paranoid interpretation.

## 4. Severity interpretation

This behaves more like an Important-class candidate than an ordinary Moderate issue. The patch fixes a verifier state tracking error, not a simple crash-only condition. The realistic exploitation evidence is not a ready-made arbitrary write primitive, so the conservative score should not assume Critical impact. However, verifier versus runtime mismatches in BPF are security-sensitive because they can invalidate the verifier safety model and may lead to kernel memory access outside intended bounds. Manual review is required to determine whether the incorrect delta propagation can be converted into a reliable read, write, or LPE primitive.

## 5. One-sentence report phrase

A BPF verifier linked-register delta tracking bug can create a verifier versus runtime mismatch when the same register is used as both source and destination, potentially allowing unsafe BPF memory access and local privilege escalation by a user with BPF loading capability.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is a BPF verifier correctness bug reported by a security research group and affecting verifier/runtime consistency, which is a known high-risk class even when the concrete exploit primitive is not demonstrated in the patch.

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

Patch: bpf: Fix linked reg delta tracking when src_reg == dst_reg [ Upstream
Commit: d88e8e4a3b52bd5b2ff3eceba4b29d1b5506d066
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d88e8e4a3b52bd5b2ff3eceba4b29d1b5506d066

Changed files:
  kernel/bpf/verifier.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=d88e8e4a3b52bd5b2ff3eceba4b29d1b5506d066

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

The original Linux kernel CVE announcement for CVE-2026-53092 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53092

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:L/PR:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 6
  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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).