[CVE-2026-72401][LOW] bpf: Fix insn_aux_data leak on verifier err_free_env path [ Upstream

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

CVE: CVE-2026-72401
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: bpf: Fix insn_aux_data leak on verifier err_free_env path [ Upstream
Commit: d8df91756890de058646597367507b239a6d2025
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d8df91756890de058646597367507b239a6d2025
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72401
Analysis date: Sun, 16 Aug 2026 01:34:10 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: YES

Summary:
A BPF verifier error path could leak env insn_aux_data when a later allocation fails, causing only a local cumulative memory exhaustion risk and no supported memory corruption or privilege escalation primitive.

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

The original Linux kernel CVE announcement for CVE-2026-72401 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72401

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: 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-2026-72401	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'bpf_check can leak env insn_aux_data when that allocation succeeds but a later env succ allocation fails and the verifier jumps directly to err_free_env. This is a local resource leak in an error path rather than a use after free or out of bounds memory corruption primitive. For the CVSS the PR:L is used for the paranoid score because some deployments may allow unprivileged BPF loading or delegate BPF access to a local service or container context. The issue is not network reachable and requires local BPF program submission plus an allocation failure condition. Impact is denial of service through cumulative memory exhaustion only, with no supported confidentiality or integrity impact from the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-72401 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 2f69c5685427308d2f312646779313f3677536bc YES  NO NO unknown 	MAYBE	BPF SIMPLEFIX LEAK LINUS 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Requires admin/root/CAP_* in typical deployments: -2. BPF program loading is normally gated by CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN, root-controlled sysctls, or product policy.
* Availability impact realistic: +1. A repeated leak could contribute to memory exhaustion, but only on a verifier error path after a later allocation failure.
* No memory corruption signal. The patch fixes a missed vfree(), not UAF, OOB, double-free, type confusion, or arbitrary write.
* No confidentiality or integrity signal. The leaked object is kernel memory that becomes unreachable, not exposed to userspace or used after free.

Paranoid signals:

* Local unprivileged trigger: +1 only for configurations where unprivileged BPF is enabled or BPF loading is delegated to a less privileged local context.
* Local unprivileged high-control kernel data-plane API refinement: +1 only under the same unprivileged/delegated BPF assumption.
* Availability impact realistic: +1 for cumulative memory exhaustion under repeated triggering.
* Hard condition / allocation failure required: -1. The leak requires env->insn_aux_data allocation to succeed and a later env->succ allocation to fail.

## 3. Reachability analysis

The bug is reachable through bpf_check() during BPF verifier processing. In typical hardened or enterprise product configurations, unprivileged BPF is disabled and loading BPF programs requires administrative capabilities, so conservative reachability is privileged local only.

If a deployment enables unprivileged BPF or delegates BPF loading to containers or services, a local lower-privileged actor may be able to hit the path. Even then, reliable impact requires repeated verifier submissions plus a specific allocation failure condition, making practical exploitation for DoS less direct than ordinary BPF verifier memory corruption bugs.

The issue is not network reachable.

Call-site confidence: high. The patch is inside bpf_check() cleanup logic and directly shows the allocation cleanup path.

## 4. Severity interpretation

This behaves like an ordinary Low/Moderate resource leak, not an Important-class kernel vulnerability. The patch does not show memory corruption, stale object reuse, attacker-controlled reclaim, type confusion, callback control, arbitrary read/write, or a security-boundary bypass.

Theoretical impact is cumulative memory exhaustion. Realistic impact is limited because the leak occurs only on an error path requiring a later allocation failure, and BPF access is privileged in typical deployments.

## 5. One-sentence report phrase

A BPF verifier error path could leak env insn_aux_data when a later allocation fails, causing only a local cumulative memory exhaustion risk and no supported memory corruption or privilege escalation primitive.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED.

Reason: this is a BPF verifier resource leak on an allocation-failure cleanup path, with no UAF/OOB/write primitive and no confidentiality or integrity impact. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.

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

Patch: bpf: Fix insn_aux_data leak on verifier err_free_env path [ Upstream
Commit: d8df91756890de058646597367507b239a6d2025
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d8df91756890de058646597367507b239a6d2025

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=d8df91756890de058646597367507b239a6d2025

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

The original Linux kernel CVE announcement for CVE-2026-72401 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72401

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 0
  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).