[CVE-2026-45873][LOW] netfilter: nft_set_rbtree: check for partial overlaps in anonymous sets [ Upstream

[CVE-2026-45873][LOW] netfilter: nft_set_rbtree: check for partial overlaps in anonymous sets [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45873
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: netfilter: nft_set_rbtree: check for partial overlaps in anonymous sets [ Upstream
Commit: 7ca5813e1b21ef300e04593f47b073ef3217aac6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7ca5813e1b21ef300e04593f47b073ef3217aac6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45873
Analysis date: Wed, 27 May 2026 08:51:55 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-45873 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45873

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-45873	LOW	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:L/A:N';*CWE-20;CWE-697;CWE-284;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'nft_set_rbtree could accept partially overlapping intervals in anonymous nftables sets because overlap validation skipped some start element checks. This can produce an invalid or ambiguous interval set and may weaken the expected packet filtering policy if a management component relies on the kernel to reject such overlaps. For the CVSS the PR:L is used for the paranoid case because a delegated or containerized network administrator may be able to submit nftables rules without full host root privileges. The issue is not directly network reachable and is triggered by local control plane rule updates rather than packet traffic. Impact is mainly a low confidentiality and integrity policy bypass in the paranoid interpretation, not memory corruption or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	REMOTE NETFILTER  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	guess

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

ActionableScore=2

1. ActionableScore
* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2. Creating or updating nftables sets normally requires CAP_NET_ADMIN.
* Integrity impact plausible: +1. Invalid overlapping intervals may weaken intended firewall policy or produce ambiguous rule semantics.
* Confidentiality impact plausible: +1 in paranoid interpretation only. A weakened filtering policy could indirectly expose traffic, but there is no direct data disclosure primitive.
* Broad/default/common subsystem: +1. nf_tables is a common Linux firewall subsystem, but this issue is in a control-plane set insertion path, not the packet fast path.
* No memory corruption signal. The patch fixes validation logic and does not show UAF, OOB write, double free, refcount corruption, or page-cache corruption.
* No reliable kernel crash signal. The described failure is acceptance of invalid overlapping intervals, not panic or lockup.
* No remote/network-triggerable signal. Packets do not directly trigger the bug. Rule updates trigger it.

3. Reachability analysis
The bug is triggered by userspace submitting nftables anonymous interval sets with partially overlapping ranges. In normal host deployments this requires CAP_NET_ADMIN, so an ordinary local user cannot trigger it directly. In containerized or delegated network administration setups, a less trusted actor may have CAP_NET_ADMIN inside a namespace or via a management service, but the impact is usually limited to the ruleset they are allowed to manage unless that service controls host firewall policy. The path is not remotely reachable through packet traffic.

4. Severity interpretation
This behaves like an ordinary Moderate or Low-like policy validation issue, not an Important-class kernel vulnerability. The realistic impact is incorrect acceptance of malformed or overlapping nftables interval rules, which may weaken expected filtering behavior. There is no evidence of memory corruption, privilege escalation, sensitive file or fd theft, kernel crash, or persistent system-wide corruption. Theoretical policy bypass risk exists, but exploitation requires control over firewall rule configuration.

5. One-sentence report phrase
nft_set_rbtree could accept partially overlapping intervals in anonymous nftables sets, potentially weakening expected firewall policy semantics when a privileged or delegated rule manager submits malformed interval rules.

6. Manual review recommendation
NO MANUAL CHECK NEEDED
The issue is a local CAP_NET_ADMIN control-plane validation bug with no demonstrated memory corruption, crash, privilege escalation, or direct network trigger.

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

Patch: netfilter: nft_set_rbtree: check for partial overlaps in anonymous sets [ Upstream
Commit: 7ca5813e1b21ef300e04593f47b073ef3217aac6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7ca5813e1b21ef300e04593f47b073ef3217aac6

Changed files:
  net/netfilter/nft_set_rbtree.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=7ca5813e1b21ef300e04593f47b073ef3217aac6

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

The original Linux kernel CVE announcement for CVE-2026-45873 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45873

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:N/I:L/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
  The Best / paranoid CVSS score: 4.4

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: unknown
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).