[CVE-2026-99288][IMPORTANT] inet: reject unhashed sockets during established lookups [ Upstream

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

CVE: CVE-2026-99288
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: inet: reject unhashed sockets during established lookups [ Upstream
Commit: d69100340b4cae08d40f898f1b601032403f6be6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d69100340b4cae08d40f898f1b601032403f6be6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99288
Analysis date: Tue, 10 Nov 2026 22:06:55 -0400
ActionableScore: 6
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
Remote TCP traffic can drive a SLAB_TYPESAFE_BY_RCU socket-reuse race that returns an unhashed replacement request socket to TCP receive processing and can panic the host.

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

The original Linux kernel CVE announcement for CVE-2026-99288 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99288

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-2026-99288	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-99288 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT IMPORTANT AEGIS_AS=4 LEGACY=IMPORTANT RESULT=SAME INDEPENDENT_LEGACY=MODERATE_KPANIC INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_HARD_VETO PRE_MERGE_LEGACY=MODERATE_KPANIC (final reconciliation agrees; DECISION: both 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:H/I:H/A:H';CWE-362;*CWE-416;**CWE-476;*CWE-672;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.1';DESCR 'A lockless TCP established ehash lookup can retain an old socket address while SLAB_TYPESAFE_BY_RCU allows that address to be reused for a new request socket. If the replacement object has the same tuple, the lookup can acquire its reference and return it even though its nulls node is unhashed. The demonstrated SYN cookie path returns a request socket with a NULL rsk_listener and tcp_v4_rcv can then cause a kernel panic. The related direct free paths can also violate a transient reference held by a stale lookup, which makes this a plausible use after free candidate even though information disclosure or code execution is not demonstrated. For the CVSS the PR:N value is selected because unauthenticated TCP traffic can reach the lookup path without a local user context. AC:H reflects the required race, address reuse, matching tuple, and request socket timing. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 8.1 and the production ActionableScore returned 6 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because FD false positive review allowed a downgrade. final reconciliation stage MODERATE_KPANIC to IMPORTANT because a specific evidence based protection or manual review veto was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH and TEMP_KPANIC_MERGE_IMPORTANT_VETO. The independent weaker Aegis shadow evaluated CVSS 5.9 and ActionableScore 4 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was IMPORTANT. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	MAYBE	REMOTE OOB NULLPTR INIT LEAK NETWORK KERNEL_PANIC_PLUS_UAF TIMER HARDWARE IPV6 KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH TEMP_KPANIC_MERGE_IMPORTANT_VETO	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 6.
* Conservative score: 6; no floor or cap applied.
* Raw paranoid score: 6.
* Paranoid score: 6; no additional primitive is sufficiently supported.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 real active-object lifetime violation: a lockless reader retains an old slab address across free/reuse and acquires a reference to the replacement request socket.
* +2 remote reachability: unauthenticated TCP traffic reaches established-socket lookup and the SYN-cookie request path used by the reproducer.
* +1 attacker-influenced lifetime/reuse sequence: the PoC drives request-socket reuse with a matching tuple, materially affecting the ABA transition.
* +1 reliable host crash: the returned unhashed request has a NULL listener and `tcp_v4_rcv()` produces a fatal interrupt-context fault.
* +1 common packet-processing path: IPv4/IPv6 established lookup feeds normal TCP receive processing.
* -1 hard timing/reuse requirement: exploitation requires a lockless lookup race, slab-address reuse, matching tuple, and request-socket timing.

Not awarded: controlled arbitrary reclaim contents, directed write, callback control, disclosure, C/I impact, or LPE. Structured stale-object leverage is not separately scored because the demonstrated downstream consumption terminates in a NULL dereference. No extra Availability point is added for the same crash. This is not B5-R: no retry-accumulated OOB write exists.

3. Reachability analysis

The evidenced actor is a remote, unauthenticated TCP peer; no local UID, capability, namespace privilege, prior privileged setup, special hardware, or host-admin operation is shown as necessary. The attacker can drive SYN-cookie request creation and matching traffic, although successful address reuse requires difficult timing. The PoC establishes feasibility, not reliability or non-crash exploitation.

4. Primitive and severity reading

This is a SLAB_TYPESAFE_BY_RCU ABA/lifetime violation involving active structured socket state, not fixed stale storage. A stale address for the retired socket resolves to a newly reused, unhashed request socket; lookup accepts it after taking the replacement object's reference, and privileged host TCP receive code consumes it as a valid established result.

The shown effect is a host kernel panic. The patch also replaces direct request frees with `reqsk_put()` where transient lookup references may exist, reinforcing the lifetime diagnosis. No specific repeated release through the same dangling reference is shown.

The primitive is CLASS_B rather than CLASS_A because attacker-controlled replacement contents, arbitrary memory access, or useful corruption past the crash is not demonstrated. ImportantCandidate is YES and auto-downgrade is disallowed because remote attacker-influenced active structured state crosses into host TCP processing, while exploit leverage beyond the demonstrated crash remains unresolved.

5. One-sentence report phrase

Remote TCP traffic can drive a SLAB_TYPESAFE_BY_RCU socket-reuse race that returns an unhashed replacement request socket to TCP receive processing and can panic the host.

6. Manual review advice

MANUAL CHECK REQUIRED

Review whether alternate replacement state or downstream consumers provide leverage beyond the demonstrated NULL-dereference panic.

7. Call-site confidence

Call-site confidence: high

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

Patch: inet: reject unhashed sockets during established lookups [ Upstream
Commit: d69100340b4cae08d40f898f1b601032403f6be6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d69100340b4cae08d40f898f1b601032403f6be6

Changed files:
  net/ipv4/inet_connection_sock.c
  net/ipv4/inet_hashtables.c
  net/ipv4/syncookies.c
  net/ipv4/tcp_input.c
  net/ipv6/inet6_hashtables.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=d69100340b4cae08d40f898f1b601032403f6be6

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

The original Linux kernel CVE announcement for CVE-2026-99288 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99288

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 6

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).