[CVE-2026-45933][LOW] bpf: Preserve id of register in sync_linked_regs() [ Upstream

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

CVE: CVE-2026-45933
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: bpf: Preserve id of register in sync_linked_regs() [ Upstream
Commit: 58059335e46537de682db84984f7716c813208c4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=58059335e46537de682db84984f7716c813208c4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45933
Analysis date: Wed, 27 May 2026 20:41:21 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
An eBPF verifier linked-register tracking bug can lose scalar id relationships during bounds synchronization, causing valid BPF programs to be rejected and producing a local BPF availability impact.

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

The original Linux kernel CVE announcement for CVE-2026-45933 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45933

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: LOW
Manual review required: NO

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-2026-45933	LOW	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:N/I:N/A:L';CWE-682;CWE-670;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '3.3';DESCR 'An eBPF verifier state tracking bug can corrupt scalar register identity during sync_linked_regs(), because bounds are copied from a linked register while the original register id is not preserved. This can break later linked-register bound propagation and make the verifier believe that an impossible division by zero path is reachable, causing valid BPF programs to be rejected. For the CVSS the PR:L is used in the paranoid score because a local user or service with BPF program load permissions can trigger the verifier path, while many deployments restrict this interface with CAP_BPF or CAP_SYS_ADMIN. The issue is not network reachable. Impact is limited to availability of BPF program loading or dependent services, with no supported evidence of kernel memory corruption, information disclosure, privilege escalation, or acceptance of unsafe BPF code.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) 	MAYBE	BPF LINUS 	-	-	checked

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

ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

* Local trigger with BPF load permissions: +1
  The verifier path is reachable by loading a crafted BPF program, but many deployments restrict this to CAP_BPF, CAP_SYS_ADMIN, or trusted services.

* Local high-control kernel API: +1 in paranoid scoring only
  BPF is a high-control verifier-facing API, but here the demonstrated effect is verifier over-rejection, not unsafe program acceptance.

* Availability impact realistic: +1
  The bug can reject valid BPF programs and disrupt BPF-dependent workloads or tests.

* Requires privileged BPF access in typical deployments: -2 conservative
  Unprivileged BPF is commonly disabled, and BPF program loading is usually capability-gated.

* No memory corruption: +0
  The issue is verifier scalar identity tracking. The patch does not indicate UAF, OOB write, arbitrary write, type confusion, or kernel heap corruption.

* No privilege escalation plausible: +0
  The described failure is a false verifier rejection due to lost linked-register bounds, not acceptance of an unsafe program.

## 3. Reachability analysis

A user or service able to load BPF programs can trigger the verifier path. In typical production systems this requires CAP_BPF, CAP_SYS_ADMIN, or a privileged loader service, although delegated BPF environments may reduce the effective privilege barrier. Namespaces do not automatically make this unprivileged unless BPF loading is explicitly exposed.

The path is not network reachable. Exploitation is realistic only as local disruption of BPF program loading, not as kernel compromise.

## 4. Severity interpretation

This behaves like Low or ordinary Moderate. The bug is in a security-sensitive subsystem, but the observed direction is conservative verifier behavior: a valid program can be rejected because bounds are not propagated correctly. There is no evidence that unsafe BPF programs are accepted, and no supported memory corruption or LPE primitive.

## 5. One-sentence report phrase

An eBPF verifier linked-register tracking bug can lose scalar id relationships during bounds synchronization, causing valid BPF programs to be rejected and producing a local BPF availability impact.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch supports a false-reject verifier precision bug only, with no demonstrated unsafe acceptance, memory corruption, information disclosure, or privilege escalation path.

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

Patch: bpf: Preserve id of register in sync_linked_regs() [ Upstream
Commit: 58059335e46537de682db84984f7716c813208c4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=58059335e46537de682db84984f7716c813208c4

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=58059335e46537de682db84984f7716c813208c4

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

The original Linux kernel CVE announcement for CVE-2026-45933 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45933

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 3.3

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: 1
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).