[CVE-2026-64354][MODERATE 7.0] bpf: Validate BTF repeated field counts before expansion

[CVE-2026-64354][MODERATE 7.0] bpf: Validate BTF repeated field counts before expansion

[AL-KERNEL]

CVE: CVE-2026-64354
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Validate BTF repeated field counts before expansion
Commit: c5ff816d5f13900c3f1f3298cfcc61339e056e56
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c5ff816d5f13900c3f1f3298cfcc61339e056e56
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64354
Analysis date: Sat, 25 Jul 2026 12:34:06 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A malformed BTF object can overflow the repeated-field count calculation during BPF_BTF_LOAD and cause btf_repeat_fields() to copy past the fixed BTF_FIELDS_MAX scratch array, resulting in local kernel memory corruption with at least DoS impact and plausible privilege-escalation concern in delegated BPF environments.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64354 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64354

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-2026-64354	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-190;*CWE-787;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'An integer overflow in BTF repeated field expansion can let a malformed user supplied BTF object bypass the remaining capacity check during BPF_BTF_LOAD. The wrapped count can make btf_repeat_fields copy more expanded fields than the fixed BTF_FIELDS_MAX scratch array can hold, resulting in an out-of-bounds write in kernel memory. For the CVSS the PR:L is used because a local process that can invoke BPF_BTF_LOAD or has delegated BPF capability can supply the malformed BTF data. The issue is not network reachable and requires local access to the BPF control path. Impact is at least local denial of service via kernel memory corruption and in the worst case may allow privilege escalation, so confidentiality and integrity are included for the paranoid score.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	BPF SIMPLEFIX IMPROVEONLY LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, strong corruption primitive: +2. The patch fixes an integer overflow that can let `memcpy()` write past the fixed `BTF_FIELDS_MAX` scratch array.
* Reliable kernel crash / strong DoS: +1. An OOB write in kernel memory during `BPF_BTF_LOAD` is a realistic crash path.
* Integrity impact plausible: +1. The primitive is a kernel OOB write, even if the exact overwrite target is not demonstrated.
* Broad/common subsystem exposure: +1. BPF/BTF is a common kernel subsystem, but access is commonly privilege gated.
* Requires admin/root/CAP_* in typical deployments: -2. In many product configurations, unprivileged BPF is disabled and BTF loading requires privileged BPF access.
* Corruption primitive constrained or target not demonstrated: -1. The patch proves an OOB write, but does not show arbitrary target selection, attacker-controlled reclaim, or a full arbitrary write primitive.

Paranoid elevation:

* Weak LPE concern: +1. A local kernel OOB write in a rich parser reachable through BPF control paths can plausibly become privilege escalation in reduced-capability or delegated-BPF environments.
* Confidentiality impact plausible in worst case: +1. Not proven, but defensible for manual triage because successful exploitation of kernel memory corruption may expose kernel or privileged state.
* Paranoid score is capped at 6 under the BPF privilege-gating rule because the provided input does not show a proven unprivileged trigger, working LPE exploit, arbitrary read/write, page-cache corruption, or namespace escape.

## 3. Reachability analysis

The bug is triggered through `BPF_BTF_LOAD` with malformed user-supplied BTF data. In typical hardened deployments, unprivileged BPF is disabled, so triggering usually requires root, `CAP_BPF`, `CAP_SYS_ADMIN`, or an equivalent privileged BPF-loading context. Namespaces or containers matter if BPF capability is delegated to a reduced-privilege service or container root, because that is not equivalent to full host-root and may turn this into a meaningful privilege-boundary issue. The path is not network reachable. Realistic exploitation requires local access to the BPF control path and a configuration that permits the attacker to load BTF.

Call-site confidence: medium. The patch and commit directly identify `BPF_BTF_LOAD`, `btf_repeat_fields()`, the fixed scratch array, and the following `memcpy()`, but not the full caller-local memory layout after the array.

## 4. Severity interpretation

This is not an ordinary low-risk validation fix because the failed validation leads to a concrete kernel OOB write. Conservative handling is borderline/manual-review because BPF access is privilege gated in the evaluated configuration and the overwrite target is not shown to be arbitrary. Paranoid handling reaches Actionable Moderate because kernel memory corruption in BPF parsing can plausibly become LPE in environments with delegated BPF privileges or reduced-capability root. It should not be auto-closed.

## 5. One-sentence report phrase

A malformed BTF object can overflow the repeated-field count calculation during BPF_BTF_LOAD and cause btf_repeat_fields() to copy past the fixed BTF_FIELDS_MAX scratch array, resulting in local kernel memory corruption with at least DoS impact and plausible privilege-escalation concern in delegated BPF environments.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch fixes a user-supplied input path that reaches a concrete kernel out-of-bounds write. Even though typical deployments gate BPF access behind privileges, the memory-corruption primitive and possible reduced-capability BPF delegation make this unsuitable for automatic closure.

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

Patch: bpf: Validate BTF repeated field counts before expansion
Commit: c5ff816d5f13900c3f1f3298cfcc61339e056e56
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c5ff816d5f13900c3f1f3298cfcc61339e056e56

Commit description:

btf_parse_struct_metas() walks user-supplied BTF during BPF_BTF_LOAD,
and btf_repeat_fields() expands repeatable fields from array elements
into the fixed BTF_FIELDS_MAX scratch array used by btf_parse_fields().

The remaining-capacity check performs the expanded field count calculation
in u32. A malformed BTF can wrap that calculation, causing the check to
pass even when the expanded field count exceeds the scratch array
capacity. The following memcpy() can then write past the end of the
array.

Use checked addition and multiplication before copying repeated fields
and reject impossible counts.

Fixes: 797d73e ("bpf: Check the remaining info_cnt before repeating btf fields")
Cc: stable@vger.kernel.org
Signed-off-by: Paul Moses <p@1g4.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260605234301.1109063-1-p@1g4.org
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/bpf/btf.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=c5ff816d5f13900c3f1f3298cfcc61339e056e56

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

The original Linux kernel CVE announcement for CVE-2026-64354 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64354

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:L/UI:N/S:U/C:L/I:L/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: 4
  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).