[CVE-2026-45838][MODERATE REGULAR] bpf: fix end-of-list detection in cgroup_storage_get_next_key() [ Upstream

[CVE-2026-45838][MODERATE REGULAR] bpf: fix end-of-list detection in cgroup_storage_get_next_key() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45838
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: fix end-of-list detection in cgroup_storage_get_next_key() [ Upstream
Commit: b4b5a20bed82130da2f2818f04d52378952fbd0b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b4b5a20bed82130da2f2818f04d52378952fbd0b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45838
Analysis date: Wed, 27 May 2026 06:09:07 -0400
ActionableScore: 4
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
`cgroup_storage_get_next_key()` can mis-detect the end of a BPF cgroup storage list and copy key bytes from a bogus object aliasing internal map fields to userspace, resulting in a limited local kernel information disclosure.

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

The original Linux kernel CVE announcement for CVE-2026-45838 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45838

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 REGULAR
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-2026-45838	MODERATE	CHECK	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:N/A:N';CWE-125;*CWE-200;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'cgroup_storage_get_next_key used list_next_entry for list iteration, but the helper wraps to the list head instead of returning NULL at the end. As a result the end of the BPF cgroup storage list could be treated as a fake storage object and storage key bytes copied back to userspace from internal map fields. For the CVSS the PR:L is used for the paranoid score because BPF map file descriptors or BPF capabilities can be delegated to reduced capability service accounts or container root in some deployments. The issue is a limited kernel information disclosure rather than a write primitive or use after free. Impact is confidentiality only, with no direct integrity, availability, or privilege escalation evidence from the patch.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)	YES	BPF SIMPLEFIX IMPROVEONLY LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=4
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Weak/indirect corruption candidate: +1. `list_next_entry()` wraps to the list head and the code interprets that address as a `bpf_cgroup_storage` object, but the demonstrated operation is a read of a bogus object, not a write.
* Confidentiality impact plausible: +1. `storage->key` from the bogus object is copied to userspace, potentially exposing internal BPF map fields or kernel-adjacent data.
* Broad/high-risk subsystem exposure: +1. BPF map operations are security-sensitive and often useful as exploit-chain enablers.
* Requires privileged BPF/cgroup storage access in typical deployments: -2. Creating or using these maps usually requires BPF privileges, cgroup privileges, or an already delegated map fd.

Conservative total: 1.

Paranoid signals:

* Weak/indirect corruption candidate: +1.
* Confidentiality impact plausible: +1.
* Broad/high-risk BPF subsystem: +1.
* Local high-control kernel API context: +1. If a map fd or BPF capability is delegated to a reduced-privilege service, container root, or sandboxed process, the attacker can repeatedly exercise `get_next_key()` and receive copied-out data.
* No full `CAP_*` penalty in delegated scenarios: 0 penalty. In that model the attacker is not equivalent to full host root.

Paranoid total: 4.

No strong memory corruption, UAF, OOB write, arbitrary write, kernel crash, or direct LPE signal is supported by the patch.

## 3. Reachability analysis

The bug is triggered through `cgroup_storage_get_next_key()` on a BPF cgroup storage map. In a strict host model, the attacker usually needs privileged BPF/cgroup access or an already opened map fd, so this is not generally unprivileged. In containerized or service-oriented deployments, BPF map fds or BPF-related capabilities may be delegated to less trusted components, making PR:L-style practical risk plausible.

The path is local only and not network reachable. It is not a default packet-processing or filesystem path. Realistic exploitation is mainly limited kernel information disclosure from internal map/list fields, not code execution.

## 4. Severity interpretation

This behaves like a BPF information disclosure issue rather than an Important-class memory corruption vulnerability. The theoretical concern is that bogus object interpretation can leak kernel-internal values that may help later exploit chains. The realistic evidence from the patch is readback of an incorrect `storage->key` to userspace, with no write primitive, no UAF, no crash, and no direct privilege escalation.

This is best treated as borderline Moderate requiring manual review, especially where BPF access is delegated.

## 5. One-sentence report phrase

`cgroup_storage_get_next_key()` can mis-detect the end of a BPF cgroup storage list and copy key bytes from a bogus object aliasing internal map fields to userspace, resulting in a limited local kernel information disclosure.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED.

Reason: this is a BPF information leak from internal map fields and may assist exploit chains, but the patch does not show a write primitive, UAF, direct LPE, or system-wide DoS.

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

Patch: bpf: fix end-of-list detection in cgroup_storage_get_next_key() [ Upstream
Commit: b4b5a20bed82130da2f2818f04d52378952fbd0b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b4b5a20bed82130da2f2818f04d52378952fbd0b

Changed files:
  kernel/bpf/local_storage.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=b4b5a20bed82130da2f2818f04d52378952fbd0b

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

The original Linux kernel CVE announcement for CVE-2026-45838 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45838

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:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 5.5

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: 1
  Paranoid ActionableScore: 4

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).