[CVE-2026-98300][MODERATE REGULAR] tcp: Don't call skb_clone_and_charge_r() for close()d listener in tcp_v6_do_rcv(). [ Upstream

[CVE-2026-98300][MODERATE REGULAR] tcp: Don't call skb_clone_and_charge_r() for close()d listener in tcp_v6_do_rcv(). [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98300
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: tcp: Don't call skb_clone_and_charge_r() for close()d listener in tcp_v6_do_rcv(). [ Upstream
Commit: a23a3bc5004df6434de05797e0b6b2ecf864b86a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a23a3bc5004df6434de05797e0b6b2ecf864b86a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98300
Analysis date: Sat, 10 Oct 2026 23:33:14 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98300 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98300

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 REGULAR
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-2026-98300	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98300 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE AEGIS_AS=0 LEGACY=MODERATE RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A race between IPv6 TCP packet processing and close of a listening socket can change the socket state from TCP_LISTEN to TCP_CLOSE before tcp_v6_do_rcv checks it. This may cause skb_clone_and_charge_r to run without the expected socket locking and leave sk_forward_alloc accounting inconsistent, which is detected as a warning during inet_sock_destruct. Reliable triggering requires an incoming IPv6 TCP packet, enabled receive option processing, control over a listening socket, and a narrow timing window around close. For the CVSS the PR:L reflects that a local user or process normally needs to create and close the listener even though network traffic contributes to the race. The issue is not treated as independently remotely exploitable because a remote sender cannot normally control the required local close operation. The demonstrated impact is limited availability degradation and a kernel warning. A host crash is plausible mainly on systems configured with panic_on_warn, while no UAF, OOB access, information leak, or write primitive is established.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	REMOTE DANGER RACE UAF NETWORK SKB KERNEL_PANIC_PLUS_UAF HARDWARE IPV6 PACKET  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

======================================================================
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 was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +1 Local unprivileged trigger. An ordinary user can create an IPv6 TCP listener on a nonprivileged port, enable the relevant receive options, generate traffic, and race packet processing against close.
* +1 Common networking packet-processing path. The defect is in the IPv6 TCP receive path and affects socket accounting during ordinary packet handling.

Negative signals:

* No timing penalty. The commit identifies a small race window, but creation, traffic, and close can be retried cheaply by the same local process. The evidence does not establish a materially uncontrollable one-shot race.
* No host-admin penalty. The complete socket lifecycle does not require host-administrator powers.
* No rare-subsystem or hardware penalty. No special hardware or unusual kernel facility is required.

Important non-awarded signals:

* Remote reachability +2 was not awarded because a remote sender cannot normally control the concurrent local close operation.
* Reliable kernel crash +1 was not awarded because the demonstrated result is WARN_ON from inconsistent `sk_forward_alloc`, not an inherent panic. `panic_on_warn` is an environmental configuration.
* No UAF, OOB access, arbitrary write, controlled reclaim, persistent reference leak, or repeated lifetime mutation is established.
* No additional availability point was awarded for the same warning.
* B5-R does not apply because there is no heap OOB write or retry-accumulated offset.
* B3-PENDING does not apply because no shared-backing write is present.
* B4-PENDING does not apply because no authorization decision is bypassed.

3. Reachability analysis

The evaluated attacker is an ordinary local process using standard IPv6 TCP socket operations. It can create and close a listener, enable the receive-option path represented by `np->rxopt.all`, and repeatedly generate packets while another thread closes the socket.

No UID 0, host capability, namespace capability, prior privileged setup, special device, boot option, or hardware prerequisite is established. Network traffic contributes to the race, but traffic alone is insufficient because the attacker must also influence the listener close transition. The complete trigger is therefore local rather than independently remote.

Although the race window is described as small, repeated attempts are inexpensive and attacker-driven. This does not justify a hard-race subtraction.

4. Primitive and severity interpretation

The exact primitive is a lockless call to `skb_clone_and_charge_r()` after the socket state changes from `TCP_LISTEN` to `TCP_CLOSE`. This leaves socket memory accounting inconsistent and is later detected by `inet_sock_destruct()` as a warning involving `sk_forward_alloc`.

There is no stale post-lifetime object use and no evidence that the socket has already been freed when the accounting operation occurs. There is also no repeated put, release, free, or refcount mutation on a dangling reference.

This is CLASS_C invalid-state and accounting behavior. The demonstrated consequence is a kernel warning. A panic is possible on systems configured with `panic_on_warn`, but that does not establish a general host-crash primitive. No useful corruption, disclosure, integrity modification, authorization bypass, or privilege-escalation mechanism remains after excluding the warning.

ImportantCandidate is NO because no Important-preserving corruption or boundary primitive exists. AutoDowngradeAllowed is YES because the issue is constrained to a race-induced accounting inconsistency with no unresolved exploitation leverage.

5. One-sentence report phrase

A local unprivileged process can race IPv6 TCP listener closure against packet processing and cause inconsistent socket memory accounting, producing a kernel warning but no established UAF, OOB access, or exploitable corruption primitive.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The supplied patch and trace establish a constrained accounting race and warning without a memory-corruption, lifetime, authorization, or cross-boundary primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: tcp: Don't call skb_clone_and_charge_r() for close()d listener in tcp_v6_do_rcv(). [ Upstream
Commit: a23a3bc5004df6434de05797e0b6b2ecf864b86a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a23a3bc5004df6434de05797e0b6b2ecf864b86a

Changed files:
  net/ipv4/af_inet.c
  net/core/sock.c
  kernel/rcu/tree.c
  kernel/softirq.c
  kernel/smpboot.c
  kernel/kthread.c
  arch/x86/kernel/process.c
  arch/x86/entry/entry_64.S
  net/ipv6/tcp_ipv6.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=a23a3bc5004df6434de05797e0b6b2ecf864b86a

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

The original Linux kernel CVE announcement for CVE-2026-98300 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98300

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:H/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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

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).