[CVE-2026-45932][IMPORTANT] bpf: Fix tcx/netkit detach permissions when prog fd isn't given [ Upstream

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

CVE: CVE-2026-45932
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: bpf: Fix tcx/netkit detach permissions when prog fd isn't given [ Upstream
Commit: 4e0772cded109c238411f2fac36ac39302758b81
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4e0772cded109c238411f2fac36ac39302758b81
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45932
Analysis date: Wed, 27 May 2026 20:45:11 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A missing capability check in `BPF_PROG_DETACH` allowed local unprivileged users to detach tcx or netkit BPF programs without providing a program fd, bypassing network administration permissions and potentially disabling network security policy.

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

The original Linux kernel CVE announcement for CVE-2026-45932 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45932

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-2026-45932	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:H/I:H/A:H';CWE-862;CWE-284;CWE-269;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:L';BEST CVSS score: '7.8';DESCR 'A BPF_PROG_DETACH permission bug allowed tcx/netkit programs to be detached when no program fd was supplied, bypassing the expected CAP_NET_ADMIN or CAP_SYS_ADMIN check. A local unprivileged user could remove network BPF programs that may enforce filtering, isolation, accounting, or traffic policy on tcx/netkit devices. For the CVSS the PR:L is used because the attack is local and requires a user context able to issue the bpf syscall, but it does not require the network administration capability that should have protected this operation. The issue is not directly network reachable, but it can affect network security policy. Impact is mainly integrity loss through unauthorized policy removal, with possible confidentiality and availability impact depending on what the detached program enforced.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) 	MAYBE	BPF SIMPLEFIX HARDWARE LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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

ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  The commit explicitly says `BPF_PROG_DETACH` on tcx or netkit could be executed by any user when no program fd was provided.

* Security-boundary bypass with practical policy impact: +2
  The missing capability check bypasses the intended `CAP_NET_ADMIN` or `CAP_SYS_ADMIN` boundary for detaching network BPF programs.

* Cross-boundary isolation or policy bypass: +1
  tcx and netkit programs can be used for traffic filtering, container networking, isolation, accounting, or policy enforcement. Unauthorized detach can weaken boundaries between workloads.

* Local high-control kernel API: +1
  The trigger is through the BPF syscall interface, a high-control local kernel API.

* Integrity impact plausible: +1
  Unauthorized removal of a network enforcement program can directly alter security policy behavior.

* Availability impact realistic: +1
  Detaching required programs can break network policy enforcement or dependent networking functionality.

* Confidentiality impact plausible in paranoid scoring: +1
  If the detached program enforced traffic isolation or filtering, removing it may expose traffic or network resources that should have been blocked.

* Broad/security-sensitive subsystem exposure: +1 in paranoid scoring
  BPF networking hooks are security-sensitive and commonly used in modern container, routing, filtering, and observability stacks, although tcx/netkit deployment is more specific than core packet receive paths.

* No memory corruption: +0
  The patch indicates missing authorization, not UAF, OOB write, arbitrary write, or verifier memory unsafety.

* No direct remote trigger: +0
  The bug is local through `bpf()` syscall control plane, not remotely triggered by packets.

* No admin privilege penalty: +0
  The whole issue is that the operation should have required `CAP_NET_ADMIN` or `CAP_SYS_ADMIN` but did not. Applying a full admin-required penalty would hide the capability bypass.

## 3. Reachability analysis

A local user able to invoke the BPF syscall could trigger the vulnerable detach path when no program fd is supplied. The bug does not require the user to possess the network administration capability that should normally protect tcx or netkit detach operations. Namespaces and containers matter because tcx/netkit and BPF networking are often used in containerized or delegated networking setups, where a reduced-privilege user or service may be able to affect policy if the capability check is missing.

The path is not network reachable by packet input. It is a local control-plane authorization bypass. Realistic exploitation depends on tcx or netkit programs being attached and used for meaningful policy, filtering, isolation, or accounting.

## 4. Severity interpretation

This is not memory corruption and does not imply kernel code execution. However, it is more serious than an ordinary Moderate verifier or DoS issue because it is a direct permission-check bypass in the BPF network control plane. The practical impact is unauthorized removal of network BPF programs, which can disable enforcement logic and weaken security boundaries. Conservative handling is Actionable Moderate. Paranoid handling is Strong Important candidate when tcx or netkit programs enforce workload isolation or security policy.

## 5. One-sentence report phrase

A missing capability check in `BPF_PROG_DETACH` allowed local unprivileged users to detach tcx or netkit BPF programs without providing a program fd, bypassing network administration permissions and potentially disabling network security policy.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because this is a direct authorization bypass of `CAP_NET_ADMIN` or `CAP_SYS_ADMIN` in a security-sensitive BPF networking path, even though it is not a memory corruption issue.

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

Patch: bpf: Fix tcx/netkit detach permissions when prog fd isn't given [ Upstream
Commit: 4e0772cded109c238411f2fac36ac39302758b81
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4e0772cded109c238411f2fac36ac39302758b81

Changed files:
  include/linux/bpf.h
  include/linux/bpf_mprog.h
  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=4e0772cded109c238411f2fac36ac39302758b81

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

The original Linux kernel CVE announcement for CVE-2026-45932 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45932

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:L
  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: 6
  Paranoid ActionableScore: 8

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).