[CVE-2026-74364][MODERATE 7.0] bpf: Reject exclusive maps as inner maps in map-in-map [ Upstream

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

CVE: CVE-2026-74364
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Reject exclusive maps as inner maps in map-in-map [ Upstream
Commit: 3a0f73d27a8d379a8852a378b3c3208143e3b3b2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3a0f73d27a8d379a8852a378b3c3208143e3b3b2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74364
Analysis date: Sat, 15 Aug 2026 13:32:21 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-74364 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74364

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-2026-74364	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:N';CWE-284;CWE-863;CWE-693;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N';BEST CVSS score: '7.1';DESCR 'Exclusive BPF maps can bypass their single program binding when inserted into a map in map object because compatibility checks only cover maps referenced directly by a program. An unrelated local BPF program can then reach the exclusive inner map through the outer map and read or mutate contents that were expected to be accessible only to the signed or matching program. This can defeat signed loader metadata protections because a frozen metadata map may be validated against a signed hash while another program on the same host changes it through the outer map path. For the CVSS the PR:L is used because the attacker needs local ability to create or use BPF maps and programs or access a signed loader workflow, but this may be delegated and is not always full administrator access. The issue is not network reachable. Impact is primarily integrity bypass, with possible confidentiality impact for protected map contents.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-74364 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: baefdbdf6812e120c9fba9cfb101d3656f478026 YES  NO NO unknown 	MAYBE	BPF SIMPLEFIX  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	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
* Security-boundary bypass with practical sensitive-object access: +2. Exclusive BPF maps are intended to be bound to a single program hash, but map-in-map access bypasses the direct used_maps compatibility check.
* Practical exploit chain demonstrated or strongly implied: +1. The commit explicitly describes signed-loader metadata exclusivity being defeated when another program mutates the map through an outer map.
* Confidentiality impact plausible: +1. Protected map contents that should be visible only to the matching program may become reachable by an unrelated BPF program.
* Integrity impact plausible: +1. The unrelated program can mutate contents that were expected to be exclusive and validated by signed metadata.
* Broad/default/common subsystem exposure: +1 in paranoid score. BPF is a major kernel subsystem, though access is usually privilege-gated in hardened products.
* Requires BPF privileges in typical deployments: -1 conservative adjustment. This is not treated as fully unprivileged because BPF map/program operations commonly require CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN, or a signed-loader workflow.

3. Reachability analysis
The bug is locally reachable through BPF map-in-map operations. It is not network reachable. In typical hardened distributions, unprivileged BPF is disabled, so a fully unprivileged local user normally cannot trigger it directly. However, the signed-loader context matters because the attacker may be an unrelated local BPF program or reduced-privilege workflow participant rather than full host root. Namespace or container delegation could lower the practical privilege barrier if BPF access is exposed to a container root, service account, or controlled loader path.

4. Severity interpretation
This is not a memory corruption issue and does not show UAF, OOB write, arbitrary write, or kernel crash. It behaves as an access-control and integrity-boundary bypass in BPF. Realistic impact is stronger than an ordinary Moderate because it can defeat the exclusivity guarantee used by signed-loader metadata validation. Conservative handling is Actionable Moderate. Paranoid handling reaches Strong Important candidate because the affected boundary is security-relevant and the commit describes a concrete bypass scenario.

5. One-sentence report phrase
Exclusive BPF maps could be inserted into map-in-map objects, allowing an unrelated local BPF program to bypass single-program binding and read or mutate map contents that signed-loader metadata expected to remain exclusive.

6. Manual review recommendation
MANUAL CHECK REQUIRED. This is not memory corruption, but it is a BPF security-boundary bypass with explicitly described signed-loader integrity impact, so it should not be auto-closed.

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

Patch: bpf: Reject exclusive maps as inner maps in map-in-map [ Upstream
Commit: 3a0f73d27a8d379a8852a378b3c3208143e3b3b2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3a0f73d27a8d379a8852a378b3c3208143e3b3b2

Changed files:
  kernel/bpf/map_in_map.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=3a0f73d27a8d379a8852a378b3c3208143e3b3b2

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

The original Linux kernel CVE announcement for CVE-2026-74364 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74364

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:H/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
  The Best / paranoid CVSS score: 7.1

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).