[CVE-2026-45903][IMPORTANT] bpf: Fix memory access flags in helper prototypes [ Upstream

[CVE-2026-45903][IMPORTANT] bpf: Fix memory access flags in helper prototypes [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45903
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: bpf: Fix memory access flags in helper prototypes [ Upstream
Commit: fdfe75161f6e8c41a7d3023fbb815b537107b806
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fdfe75161f6e8c41a7d3023fbb815b537107b806
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45903
Analysis date: Wed, 27 May 2026 22:15:24 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
Incorrect BPF helper memory access flags may let the verifier rely on stale buffer state after helper calls, creating a local verifier-unsoundness risk for users with BPF program loading capability.

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

The original Linux kernel CVE announcement for CVE-2026-45903 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45903

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-2026-45903	IMPORTANT	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-682;CWE-693;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'Incorrect BPF helper memory access flags can make the verifier treat helper buffer contents as unchanged even when the helper actually writes to the buffer. A local attacker with BPF program load capability may craft a program that relies on stale verifier memory state after helper calls, creating a potential verifier unsoundness rather than a simple rejection bug. For the CVSS the PR:L is used because the attack requires local BPF loading ability or a delegated BPF loader context, but not necessarily full administrator control in all deployments. The issue is not directly network reachable, although some affected helpers are used by networking BPF programs. Impact is at least local denial of service or verifier correctness failure, and in the worst case may allow confidentiality, integrity, and availability impact if stale memory assumptions can be turned into unsafe program acceptance.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) 	MAYBE	INIT BPF LINUS IPV6  KPANIC INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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

ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local trigger with BPF load capability: +1
  The affected path is reachable by loading BPF programs that use the impacted helpers.

* Local high-control kernel data-plane API: +1
  BPF verifier inputs are highly attacker-controlled when BPF program loading is available.

* Security-boundary / verifier trust boundary concern: +2
  The verifier is a kernel security boundary. Incorrect helper access flags can make verifier state differ from runtime memory effects.

* Weak LPE concern: +1
  The patch does not demonstrate a concrete arbitrary write or OOB primitive, but stale verifier assumptions after helper writes are a plausible verifier-unsoundness class.

* Integrity impact plausible: +1
  If verifier assumptions are wrong, unsafe program behavior may be accepted or safety checks may be optimized incorrectly.

* Availability impact realistic: +1
  At minimum, verifier correctness bugs can cause bad runtime behavior or kernel-side faults if unsafe assumptions are reachable.

* Broad/security-sensitive subsystem exposure: +1
  BPF is broadly deployed and security-sensitive, including tracing, networking, observability, and policy use cases.

* Requires BPF permissions in many deployments: -2 conservative
  Many production systems restrict BPF loading with CAP_BPF, CAP_SYS_ADMIN, LSM policy, or privileged loaders. This penalty is not applied fully in the paranoid score because delegated BPF loaders and service accounts are common.

* No proven concrete memory corruption primitive: +0
  The patch shows verifier memory access metadata fixes, not a demonstrated UAF, OOB write, arbitrary write, or exploit.

## 3. Reachability analysis

A local user or service with BPF program loading ability can reach the affected verifier paths. In hardened deployments this usually requires CAP_BPF, CAP_SYS_ADMIN, or access through a privileged loader. In cloud, observability, container, or agent-based environments, BPF loading may be delegated to service accounts, making PR:L a reasonable paranoid interpretation.

The issue is not directly network reachable. Some affected helpers are used by networking BPF programs, but packet traffic alone does not trigger the verifier bug.

## 4. Severity interpretation

This is more than an ordinary Moderate because it affects verifier memory-state correctness. The patch does not prove memory corruption or LPE, so the conservative score stays at Actionable Moderate. The paranoid score is Strong Important candidate because BPF verifier unsoundness involving stale memory assumptions can historically become a kernel memory safety or privilege boundary issue after manual analysis.

## 5. One-sentence report phrase

Incorrect BPF helper memory access flags may let the verifier rely on stale buffer state after helper calls, creating a local verifier-unsoundness risk for users with BPF program loading capability.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because this is a BPF verifier correctness issue with potential unsafe program acceptance, even though the patch does not itself demonstrate a concrete exploit primitive.

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

Patch: bpf: Fix memory access flags in helper prototypes [ Upstream
Commit: fdfe75161f6e8c41a7d3023fbb815b537107b806
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fdfe75161f6e8c41a7d3023fbb815b537107b806

Changed files:
  kernel/bpf/helpers.c
  kernel/bpf/syscall.c
  kernel/trace/bpf_trace.c
  net/core/filter.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=fdfe75161f6e8c41a7d3023fbb815b537107b806

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

The original Linux kernel CVE announcement for CVE-2026-45903 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45903

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: 5
  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).