[CVE-2026-72111][MODERATE 7.0] bpf: Reset register bounds before narrowing retval range in check_mem_access() [ Upstream

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

CVE: CVE-2026-72111
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Reset register bounds before narrowing retval range in check_mem_access() [ Upstream
Commit: bde92f65042ec14389782dd223f706bf6b59ce5d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bde92f65042ec14389782dd223f706bf6b59ce5d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72111
Analysis date: Sat, 15 Aug 2026 08:08:01 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A BPF verifier range-tracking bug can leave stale register bounds before narrowing an LSM hook return value, creating a verifier/runtime mismatch that may bypass BPF memory safety checks and should be treated as Actionable Moderate at minimum, or Important where BPF loading is available to reduced-privilege users.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72111 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72111

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-2026-72111	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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-787;CWE-125;CWE-269;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7.8';DESCR 'A BPF verifier range tracking bug can leave stale bounds on a register before narrowing an LSM hook return value. The verifier may believe the register has a narrower value than it will have at runtime, creating a verifier/runtime mismatch that can bypass BPF memory safety checks. This is a memory safety class issue because an accepted BPF program may perform memory accesses that were validated against incorrect bounds. For the CVSS the PR:L is used for the paranoid score because BPF loading may be available to a local user, delegated service account, container root, or process with reduced BPF related capabilities rather than only to a full host administrator. The issue is local and is not network reachable by itself. Impact may include local privilege escalation, kernel memory corruption, information disclosure, and denial of service. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	WARNONLY BPF SIMPLEFIX LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative scoring:

* Memory corruption, Strong corruption primitive: +2
  The commit explicitly describes a verifier/runtime mismatch that can bypass BPF memory safety checks. This is stronger than a simple validation warning because the verifier may approve accesses based on incorrect bounds.

* Privilege escalation plausible: +2
  BPF verifier memory-safety bypasses are a well-known LPE-relevant bug class when an attacker can load the affected program type.

* Confidentiality impact plausible: +1
  Incorrect verifier bounds can plausibly allow out-of-bounds kernel reads or disclosure through BPF-accessible paths.

* Integrity impact plausible: +1
  Incorrect verifier bounds can plausibly allow unsafe writes or corruption of kernel memory/state.

* Broad/default/common subsystem: +1
  BPF verifier is a core kernel security enforcement component, even though this specific path is BPF LSM retval handling.

* Requires admin/root/CAP_* in typical deployments: -2
  In the evaluated configuration, unprivileged BPF is disabled and loading/attaching relevant BPF programs is expected to require CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN, or equivalent root-controlled setup.

Conservative raw score: 5. Conservative BPF privilege-gating cap also keeps this at 5.

Paranoid scoring:

* Local reduced-privilege/delegated trigger: +1
  If BPF loading is delegated to a service account, container root, or reduced-capability process, the attacker may not be equivalent to full host root.

* Local high-control BPF API: +1
  Applies only in the paranoid/delegated-access interpretation where the attacker can actually load relevant BPF programs.

* Memory corruption, Strong corruption primitive: +2

* Privilege escalation plausible: +2

* Confidentiality impact plausible: +1

* Integrity impact plausible: +1

* Broad/default/common subsystem: +1

Paranoid raw score is above 6, but the BPF privilege-gating rule caps it at 6 because unprivileged BPF is not assumed enabled and no working exploit or arbitrary read/write primitive is shown in the patch.

## 3. Reachability analysis

The bug is locally reachable through BPF program loading and verifier processing, specifically in the BPF LSM hook return-value path. It is not network reachable by itself.

In typical hardened or enterprise deployments, unprivileged BPF is disabled, so triggering requires root or BPF-related capabilities. However, practical risk can be higher where BPF is delegated to observability agents, service accounts, containerized workloads with extra capabilities, or reduced-capability root contexts.

Namespaces and containers matter because container root or a service account with delegated BPF rights may not be equivalent to full host root, but could still reach the verifier path. Call-site confidence: high, because the patch directly modifies `check_mem_access()` in the verifier and the commit explains the verifier/runtime mismatch.

## 4. Severity interpretation

This should not be treated as an ordinary Moderate or auto-closed issue. The realistic conservative view is an Actionable Moderate because the affected path is privilege-gated in many products. The paranoid view reaches Strong Important candidate because verifier/runtime mismatches in BPF are historically LPE-relevant and can bypass the kernel’s main safety gate for BPF memory access.

Theoretical impact includes kernel memory corruption, information disclosure, denial of service, and possible local privilege escalation. Realistic exploitation depends strongly on whether an attacker can load the relevant BPF program type in the target configuration.

## 5. One-sentence report phrase

A BPF verifier range-tracking bug can leave stale register bounds before narrowing an LSM hook return value, creating a verifier/runtime mismatch that may bypass BPF memory safety checks and should be treated as Actionable Moderate at minimum, or Important where BPF loading is available to reduced-privilege users.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a BPF verifier memory-safety bypass class issue with plausible LPE impact, even though typical deployments may gate exploitation behind privileged BPF access.

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

Patch: bpf: Reset register bounds before narrowing retval range in check_mem_access() [ Upstream
Commit: bde92f65042ec14389782dd223f706bf6b59ce5d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bde92f65042ec14389782dd223f706bf6b59ce5d

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=bde92f65042ec14389782dd223f706bf6b59ce5d

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

The original Linux kernel CVE announcement for CVE-2026-72111 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72111

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: 5
  Paranoid ActionableScore: 6

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: YES
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).