[CVE-2026-98595][LOW] udp: remove a disconnected socket from the 4-tuple hash table [ Upstream

[CVE-2026-98595][LOW] udp: remove a disconnected socket from the 4-tuple hash table [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98595
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: udp: remove a disconnected socket from the 4-tuple hash table [ Upstream
Commit: c21daf37d5ce9a4e234b7c42238ac1e6041e28e4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c21daf37d5ce9a4e234b7c42238ac1e6041e28e4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98595
Analysis date: Mon, 19 Oct 2026 02:07:01 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A disconnected UDP socket can remain in the 4-tuple hash table and impose persistent lookup overhead, but the supplied evidence establishes only constrained stale hash state and does not show memory corruption, authorization bypass, or reliable host-wide denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-98595 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98595

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-2026-98595	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98595 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both LOW)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-459;CWE-404;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A disconnected UDP socket can remain in the 4 tuple hash table because the normal rehash and unhash paths are skipped for a socket bound to a specific address and port. The stale entry keeps hash4_cnt raised and forces packets for the affected local tuple through an unnecessary 4 tuple lookup. Under sustained local socket activity this may increase packet processing cost, and relocation after SO_BINDTODEVICE may concentrate stale entries in one bucket. An IPv6 datagram from the former peer with source port zero can also match the stale entry, but this requires the socket state to have been created locally and does not by itself demonstrate unauthorized data access. For the CVSS the PR:L value is used because an unprivileged local process can create the basic stale state through UDP socket bind, connect, and disconnect operations, although some stronger relocation scenarios may require an additional capability. The issue is not independently network reachable because remote traffic cannot create the stale socket state. Impact is primarily limited availability degradation. No UAF, OOB access, information disclosure, or privilege escalation primitive is supported by the affected path. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 1 with primitive class CLASS_C and manual review NO. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	REMOTE OOB LOCK INIT NETWORK IPV6 PACKET DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 KPANIC_UNSUPPORTED_REMOVED	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

## 1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::

## 2. Signal breakdown

Positive signals:

* +1 Local unprivileged trigger. An ordinary process can bind an unprivileged UDP port, connect the socket, and disconnect it with `connect(AF_UNSPEC)`.
* +1 Common networking lookup path. The stale `hash4` membership affects subsequent UDP packet lookup for the local address and port.
* +1 Secondary index staleness. The live socket remains incorrectly registered in the 4-tuple hash table, and later lookup or rehash operations continue consuming that obsolete association.

Negative signals:

* -1 Corruption is constrained to hash-membership metadata. The socket remains alive, no freed object is accessed, and the attacker does not obtain a directed memory-write primitive.

Not awarded:

* No UAF, OOB read, OOB write, double release, or refcount corruption is established.
* No reliable kernel crash or host-wide resource exhaustion is demonstrated.
* The accumulated-bucket scenario may increase CPU cost, but substantial host-wide DoS is not established.
* The IPv6 zero-source-port match does not establish unauthorized access because the disconnected socket remains bound and can receive datagrams.
* No authorization decision changes from DENY to ALLOW.
* No protected resource, shared backing, checksum-metadata corruption, or trust-boundary crossing is established.
* B5-R does not apply because there is no retry-accumulated heap OOB write or later consumption of corrupted heap state.
* B3-PENDING does not apply because no shared or file-backed storage is modified.
* No additional paranoid point is awarded solely for sustained socket creation or packet load.

## 3. Reachability analysis

The basic stale-entry state is reachable by an ordinary local user through normal UDP `bind`, `connect`, and disconnect operations on an unprivileged port. It requires neither host UID 0 nor host-administrator capabilities.

The stronger relocation scenario uses `SO_BINDTODEVICE`, whose complete capability and namespace conditions are not established by the supplied patch. It is therefore not used to claim an unprivileged concentrated-bucket DoS.

Remote traffic cannot independently create the vulnerable socket state. An IPv6 packet from the former peer with source port zero can match only after a local process has created and disconnected the socket. No prior privileged configuration, special hardware, boot option, or race is needed for the basic defect.

## 4. Primitive and severity interpretation

The exact primitive is stale membership of a still-live UDP socket in an active 4-tuple hash table. This is a secondary-index consistency defect, not a memory-lifetime violation. The obsolete entry remains visible to packet lookup and can be moved by a later rehash, but the socket itself has not been freed.

The demonstrated consequences are unnecessary hash lookups, persistent `hash4_cnt` elevation while the socket remains alive, possible bucket concentration in the stronger relocation scenario, and an IPv6 stale-tuple match. The patch does not establish memory corruption, kernel panic, disclosure, unauthorized modification, privilege escalation, or a security-boundary bypass.

`PrimitiveClass=CLASS_C` is appropriate because the observed behavior is constrained invalid active state with potential availability degradation. `ImportantCandidate=NO` and `AutoDowngradeAllowed=YES` follow because no independently useful corruption or boundary-crossing primitive remains unresolved.

## 5. One-sentence report phrase

A disconnected UDP socket can remain in the 4-tuple hash table and impose persistent lookup overhead, but the supplied evidence establishes only constrained stale hash state and does not show memory corruption, authorization bypass, or reliable host-wide denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The issue is suitable for automatic Moderate or Low-priority handling because its demonstrated primitive is limited to stale hash membership and lookup overhead.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: udp: remove a disconnected socket from the 4-tuple hash table [ Upstream
Commit: c21daf37d5ce9a4e234b7c42238ac1e6041e28e4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c21daf37d5ce9a4e234b7c42238ac1e6041e28e4

Changed files:
  net/ipv4/udp.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=c21daf37d5ce9a4e234b7c42238ac1e6041e28e4

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

The original Linux kernel CVE announcement for CVE-2026-98595 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98595

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