[CVE-2026-90110][MODERATE 7.0] inetpeer: randomize RB-tree node comparison using SipHash [ Upstream

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

CVE: CVE-2026-90110
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: inetpeer: randomize RB-tree node comparison using SipHash [ Upstream
Commit: b20e98f0bb668a59abaf7bcf85d75c073e90d352
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b20e98f0bb668a59abaf7bcf85d75c073e90d352
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90110
Analysis date: Thu, 17 Sep 2026 17:27:16 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: NO

Summary:
The deterministic inetpeer RB-tree ordering could let an off-path network attacker predict garbage-collection behavior, selectively reset ICMP rate-limit state, and infer UDP port status through a network side channel.

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

The original Linux kernel CVE announcement for CVE-2026-90110 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90110

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: NO

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-2026-90110	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90110 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N';CWE-203;*CWE-200;CWE-693;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.8';DESCR 'The inetpeer rate limiting cache used deterministic RB tree ordering based on remote IP addresses, which made lookup paths and garbage collection candidate selection predictable to an off path network attacker. By forcing inet_peer garbage collection and selective eviction, an attacker could cause selected peer entries to be recreated with a fresh token bucket and bypass IP keyed ICMP rate limits. This creates a network side channel that can be used to infer UDP port state, similar to SAD DNS style attacks. For the CVSS the PR:N is used because the attacker does not need local code execution or an authenticated user context on the target, only network reachability and the ability to send crafted traffic patterns. The issue is network reachable but has high attack complexity because reliable use depends on shaping the peer cache, triggering garbage collection, and observing rate limit effects. Impact is mainly limited confidentiality loss and security feature bypass, with possible limited integrity relevance as an auxiliary primitive for UDP spoofing attacks. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5)	YES	REMOTE WRITE OOB LINUS KPANIC PACKET  KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS 	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=NO

## 1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap was applied.
* Final recommended bucket: **Actionable Moderate**::

## 2. Signal breakdown

Conservative signals:

* +2 Remote reachable / directly network-triggerable: the described attacker is an off-path network adversary that can influence inetpeer creation, lookup, and garbage collection through crafted traffic patterns.
* +1 Confidentiality plausible: the primitive can be used as a side channel to infer UDP port state by bypassing IP-keyed ICMP rate limits.
* +1 Common networking core path / packet-processing path: inetpeer and ICMP rate limiting are part of broadly relevant IP networking behavior.

Paranoid additional signal:

* +1 Limited integrity / security-feature-bypass relevance: resetting selected inet_peer token buckets can bypass a kernel-enforced ICMP rate-limiting mechanism and may act as an auxiliary primitive for UDP spoofing style attacks.

Non-awarded signals:

* No UAF or lifetime corruption is established.
* No memory corruption, OOB access, arbitrary write, controlled reclaim, or refcount primitive is established.
* No kernel crash or availability impact is established.
* No privilege escalation is established.
* No authorization ALLOW-vs-DENY bypass is established.
* No strong Class A primitive is established.
* No race/timing penalty is applied. The attack is complex, but the prompt requires concrete reducing signals rather than generic complexity downgrades.

## 3. Reachability analysis

The evaluated attacker is an off-path network attacker. The attacker does not need local code execution, a local account, namespace privileges, or host-admin-equivalent privileges. The complete trigger depends on the ability to send traffic that influences inet_peer entries, grows the tree beyond `inet_peer_threshold`, triggers garbage collection, and observes ICMP rate-limit behavior.

No namespace-scoped privilege is required or relevant. No prior host-admin setup is identified beyond the normal presence of IP networking and inetpeer-based rate limiting. No special hardware is required. The attack is not a simple single-packet crash. It requires shaping cache state and observing a side channel, so practical exploitation is more complex than ordinary remote DoS, but this is not used as a scoring penalty.

## 4. Primitive and severity interpretation

The exact primitive is a deterministic data-structure side channel in the inetpeer RB-tree. Because peer entries were ordered by predictable IP-address comparison, an off-path attacker could predict lookup traversal and garbage-collection candidate behavior. Selective eviction and recreation of inet_peer entries resets the ICMP rate-limiting token bucket, allowing rate-limit bypass and UDP port-state inference.

This is not active structured UAF, fixed stale storage, repeated release, refcount corruption, or kernel memory corruption. The demonstrated consequence is limited network information disclosure and security feature bypass. The speculative consequence is use as an auxiliary primitive in broader UDP spoofing or SAD DNS style attacks.

PrimitiveClass is NONE because the patch does not establish kernel corruption, lifetime violation, ownership violation, or authorization bypass. ImportantCandidate is NO because no Important-grade memory corruption, LPE, privileged resource theft, or broad security-boundary compromise is demonstrated. AutoDowngradeAllowed is NO because the issue is remotely reachable and side-channel/security-feature-bypass related, so automatic closure as ordinary low-risk noise would be unsafe.

Likely operational severity: actionable Moderate. It deserves manual triage, especially for systems where UDP services and off-path spoofing assumptions matter.

## 5. One-sentence report phrase

The deterministic inetpeer RB-tree ordering could let an off-path network attacker predict garbage-collection behavior, selectively reset ICMP rate-limit state, and infer UDP port status through a network side channel.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: network-reachable side-channel and ICMP rate-limit bypass behavior can matter for UDP spoofing threat models, even though there is no kernel memory corruption or LPE primitive.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: inetpeer: randomize RB-tree node comparison using SipHash [ Upstream
Commit: b20e98f0bb668a59abaf7bcf85d75c073e90d352
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b20e98f0bb668a59abaf7bcf85d75c073e90d352

Changed files:
  include/net/inetpeer.h
  net/ipv4/inetpeer.c
  net/ip.h
  net/inetpeer.h
  net/secure_seq.h

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=b20e98f0bb668a59abaf7bcf85d75c073e90d352

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

The original Linux kernel CVE announcement for CVE-2026-90110 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90110

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:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
  The Best / paranoid CVSS score: 4.8

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: 4
  Paranoid ActionableScore: 5

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).