[CVE-2026-45927][IMPORTANT] bpf: Require frozen map for calculating map hash [ Upstream

[CVE-2026-45927][IMPORTANT] bpf: Require frozen map for calculating map hash [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45927
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: bpf: Require frozen map for calculating map hash [ Upstream
Commit: 7752d36343862323bbeea4ce3adf0ec2ed86e122
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7752d36343862323bbeea4ce3adf0ec2ed86e122
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45927
Analysis date: Wed, 27 May 2026 20:59:32 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A BPF map hash TOCTOU bug allowed a mutable map to be hashed before freeze and then modified, letting a trusted loader validate stale hash data against changed contents and causing a local integrity bypass.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-45927 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45927

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: IMPORTANT
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-2026-45927	IMPORTANT	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:L/I:H/A:L';CWE-367;CWE-345;CWE-354;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N';BEST CVSS score: '6.6';DESCR 'A BPF map hash TOCTOU bug allowed BPF_OBJ_GET_INFO_BY_FD to calculate and cache a map hash while the map was still mutable. A local attacker could obtain a hash for one map state and then modify the map before freeze, causing a trusted loader or policy verifier to validate stale hash data against changed contents. For the CVSS the PR:L is used because the attack requires a local user or service that can operate on BPF maps or interact with a trusted loader workflow, but it does not require the attacker to possess the trust decision made by that loader. The issue is not network reachable. Impact is mainly integrity loss through bypass of map content verification, with possible limited confidentiality or availability impact depending on what the modified map controls.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) 	MAYBE	BPF SIMPLEFIX  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged or reduced-privilege trigger: +1
  The attack is local and involves userspace requesting a BPF map hash before the map is frozen, then modifying the map contents.

* Security-boundary bypass with practical sensitive-object or policy impact: +2
  The stale hash can trick a trusted loader or verifier into accepting modified map contents as if they matched the previously validated hash.

* Practical exploit chain strongly implied: +1
  The commit explicitly describes the chain: request hash, mutate map, freeze later, then trusted loader verifies stale hash against changed contents.

* Local high-control kernel API: +1
  BPF maps are a high-control local kernel API and are often used as inputs to policy, tracing, filtering, or enforcement programs.

* Integrity impact plausible: +1
  The main impact is integrity loss in the trusted loader workflow because the verified object state can differ from the loaded object state.

* Confidentiality or availability impact plausible in paranoid scoring: +1
  Depending on what the BPF map controls, modified map contents could affect policy decisions, filtering, visibility, or service behavior, but this is deployment-dependent.

* No generic kernel memory corruption: +0
  The patch does not indicate UAF, OOB write, arbitrary write, type confusion, or verifier acceptance of unsafe memory operations.

* No direct remote trigger: +0
  The issue is local through BPF map operations and trusted-loader interaction, not packet-triggered or network-reachable.

* No full admin penalty: +0
  Although many deployments restrict BPF operations, the security issue is specifically a trust validation bypass. Applying a full CAP_SYS_ADMIN or CAP_BPF penalty would understate the reduced-privilege workflow risk.

## 3. Reachability analysis

A local user or service that can create or provide BPF maps to a trusted loader workflow can trigger the bug by requesting the map hash before the map is frozen and then changing contents before final use. In many production systems direct BPF map operations may require CAP_BPF, CAP_SYS_ADMIN, or a privileged loader, but the affected trust model may involve reduced-privilege users submitting objects to a trusted component.

Namespaces and containers matter if BPF object loading or map submission is delegated to tenants, agents, CI jobs, or sandboxed services. The path is not network reachable by itself. Realistic exploitation depends on a system actually relying on BPF map hashes as a security or integrity verification mechanism.

## 4. Severity interpretation

This is not memory corruption and does not imply kernel code execution. It is, however, more serious than an ordinary Moderate because it is a TOCTOU integrity bypass in a BPF trust workflow. The realistic impact is stale-hash validation of mutable map contents, which can undermine policy verification or trusted-loader assumptions. The paranoid score treats it as an Important candidate when BPF map hashes are used as a security boundary.

## 5. One-sentence report phrase

A BPF map hash TOCTOU bug allowed a mutable map to be hashed before freeze and then modified, letting a trusted loader validate stale hash data against changed contents and causing a local integrity bypass.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because this is a trust and integrity bypass in BPF map verification workflows, even though it is not a kernel memory corruption issue.

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

Patch: bpf: Require frozen map for calculating map hash [ Upstream
Commit: 7752d36343862323bbeea4ce3adf0ec2ed86e122
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7752d36343862323bbeea4ce3adf0ec2ed86e122

Changed files:
  kernel/bpf/syscall.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=7752d36343862323bbeea4ce3adf0ec2ed86e122

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

The original Linux kernel CVE announcement for CVE-2026-45927 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45927

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:N/I:H/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:L
  The Best / paranoid CVSS score: 6.6

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: 6
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).