[CVE-2026-74305][MODERATE 7.0] bpf: Tighten cgroup storage cookie checks for prog arrays [ Upstream

[CVE-2026-74305][MODERATE 7.0] bpf: Tighten cgroup storage cookie checks for prog arrays [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74305
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Tighten cgroup storage cookie checks for prog arrays [ Upstream
Commit: 87177497cca90bf4fcfb759eb898560eb5b46a10
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=87177497cca90bf4fcfb759eb898560eb5b46a10
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74305
Analysis date: Sat, 15 Aug 2026 11:38:57 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A cgroup local storage cookie validation flaw in BPF prog arrays allows a storage-less tail-call program to bridge incompatible storage contexts, creating a plausible OOB access or type-confusion condition in a privileged local BPF control path.

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

The original Linux kernel CVE announcement for CVE-2026-74305 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74305

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
======================================================================

CVE-2026-74305	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-787;CWE-125;CWE-843;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'BPF prog array compatibility checks for cgroup local storage could incorrectly accept a storage-less program as compatible with any stored storage cookie. This allows a tail call bridge where an entry program with one cgroup storage context calls a storage-less intermediate program which can then tail call a storage-using callee with a different expected storage context. The resulting runtime mismatch can expose an out-of-bounds access or type confusion in cgroup local storage handling. For the CVSS the PR:L is used because an attacker needs local ability to load or manage relevant BPF programs and prog arrays, but this may be available to a reduced capability root, container service account, or delegated BPF capable process rather than requiring unrestricted host root. The issue is not network reachable by itself and is triggered through local BPF control plane operations. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel memory access primitives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	OOB BPF SIMPLEFIX  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
======================================================================

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 signals:

* Memory corruption, strong corruption primitive: +2. The commit explicitly references incomplete protection for OOB access in cgroup local storage, and the fixed check prevents an incompatible BPF tail-call chain from reaching a storage-using callee with the wrong runtime storage context.
* Weak LPE concern: +1. BPF verifier or runtime storage mismatches can become kernel memory access primitives, but this patch alone does not demonstrate controlled reclaim, arbitrary write, or a working LPE chain.
* Reliable kernel crash / strong DoS: +1. An invalid cgroup local storage context can plausibly lead to kernel OOB access or crash.
* Confidentiality impact plausible: +1. OOB access in BPF local storage may expose kernel or adjacent storage data, but this is not proven as a stable disclosure primitive.
* Integrity impact plausible: +1. cgroup local storage is writable by BPF programs, so a wrong storage context may plausibly become a limited write or corruption primitive.
* Practical exploit chain strongly implied: +1. The commit describes a concrete A -> B(no storage) -> C(storage) tail-call bridge that bypasses the intended storage-cookie compatibility model.
* Requires admin/root/CAP_* in typical deployments: -2. Loading and attaching relevant BPF programs and managing prog arrays normally requires CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN, or root-controlled BPF enablement.

Paranoid adjustment:

* Treat reduced-capability root, delegated BPF-capable services, or container/service-account setups as not equivalent to unrestricted host root. This weakens the privilege penalty and supports a paranoid score of 6, capped by the BPF privilege-gating rule.

## 3. Reachability analysis

The bug is locally triggered through BPF control-plane operations involving cgroup local storage, prog arrays, and tail calls. It is not network reachable by itself. In typical hardened product configurations, unprivileged BPF is disabled and the attacker needs privileged BPF or cgroup attach capabilities, so this is not a normal unprivileged user bug. However, practical deployments may delegate BPF or networking capabilities to service accounts, container roots, or reduced-capability administrators, so PR:L-style handling is reasonable for paranoid triage.

Path default exposure depends on whether BPF loading and cgroup BPF attachment are available to the attacker. The affected subsystem is security-sensitive because BPF verifier/runtime mismatches historically can produce kernel memory access bugs.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup. It is an actionable BPF safety bug because the patch fixes an incomplete OOB-access prevention mechanism in cgroup local storage and blocks a concrete incompatible tail-call bridge. Realistic exploitation is gated by BPF privileges, so the conservative score should not exceed Actionable Moderate without evidence of unprivileged reachability or a working exploit. The paranoid score reaches Strong Important candidate territory because the bug class involves BPF runtime memory-safety semantics and plausible confidentiality/integrity impact.

## 5. One-sentence report phrase

A cgroup local storage cookie validation flaw in BPF prog arrays allows a storage-less tail-call program to bridge incompatible storage contexts, creating a plausible OOB access or type-confusion condition in a privileged local BPF control path.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because the patch explicitly references incomplete OOB-access protection in BPF cgroup local storage, and the described tail-call bridge may expose a kernel memory access primitive even though normal exploitation is gated by BPF privileges.

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

Patch: bpf: Tighten cgroup storage cookie checks for prog arrays [ Upstream
Commit: 87177497cca90bf4fcfb759eb898560eb5b46a10
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=87177497cca90bf4fcfb759eb898560eb5b46a10

Changed files:
  kernel/bpf/core.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=87177497cca90bf4fcfb759eb898560eb5b46a10

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

The original Linux kernel CVE announcement for CVE-2026-74305 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74305

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: 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).