[CVE-2026-98432][IMPORTANT] ipv4: free inet_opt and ireq_opt after an RCU grace period

[CVE-2026-98432][IMPORTANT] ipv4: free inet_opt and ireq_opt after an RCU grace period

[AL-KERNEL]

CVE: CVE-2026-98432
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: ipv4: free inet_opt and ireq_opt after an RCU grace period
Commit: 11a03ce3c4a62d84c10ccdfe47f8075006498568
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=11a03ce3c4a62d84c10ccdfe47f8075006498568
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98432
Analysis date: Thu, 15 Oct 2026 22:04:29 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98432 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98432

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.

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

CVE-2026-98432	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-98432 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT TEMP_KPANIC_MERGE=IMPORTANT_HARD_VETO PRE_MERGE_LEGACY=IMPORTANT (independent Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC)	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:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in the IPv4 TCP request path can leave tcp_v4_send_synack and ip_options_build reading IP options after the child socket or a migrated request socket has freed the shared options object. A remote attacker may attempt to trigger the first path by sending an IPv4 SYN with options and retransmitting the SYN while another CPU creates and releases the corresponding child socket. The resulting use-after-free can cause an invalid read and a kernel crash. Reuse of the freed allocation may also expose limited stale data or influence packet construction, although no arbitrary write primitive is demonstrated. For the CVSS the PR:N value is used because the direct IPv4 path can be reached through pre-authentication TCP SYN traffic without a local user account. AC:H is used because successful triggering depends on concurrent processing and a narrow race window. Impact is at least a remote denial of service via kernel crash and in the paranoid case may include limited confidentiality or integrity impact due to use of freed memory. Internet exposure depends on whether an affected TCP listener is reachable and whether the required IPv4 option path is enabled by the received traffic. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 7 with recommendation Strong Important candidate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to IMPORTANT because the ActionableScore threshold rule was applied. final reconciliation stage IMPORTANT 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_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS and INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 and TEMP_KPANIC_MERGE_IMPORTANT_VETO. The independent weaker Aegis shadow evaluated CVSS 3.7 and ActionableScore 5 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. 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 Strong Important candidate (with actual score 7)	MAYBE	REMOTE BPF UAF NETWORK IPV6  KPANIC INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 TEMP_KPANIC_MERGE_IMPORTANT_VETO	-	-	checked

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

ActionableScore=7
ActionableScoreLower=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 conservative score: 6
* Conservative score: 6
* Raw paranoid score: 7
* Paranoid score: 7
* No floor or cap changed either score.
* Final recommended bucket: **Strong Important candidate**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF. `inet_opt` or `ireq_opt` can be freed while an RCU reader continues using it in `ip_options_build()`.
* +2 Direct network reachability. Pre-authentication IPv4 SYN traffic with options and retransmitted SYNs can reach the first vulnerable path through an exposed TCP listener.
* +1 Concrete RCU referenced-object lifetime mismatch. Readers legitimately use the options under `rcu_read_lock()`, but the destructor used immediate `kfree()` before their grace period completed.
* +1 Common networking path. The first issue affects IPv4 TCP request and SYNACK processing rather than an obscure control-plane-only interface.
* +1 Realistic kernel crash. Dereferencing a freed options object during packet construction can fault or corrupt the packet-building state.
* -1 Narrow concurrent window. Triggering requires SYNACK construction to overlap child-socket destruction on another CPU.

Paranoid-only signal:

* +1 Structured stale-object leverage. The stale object contains attacker-influenced IPv4 option state, and `ip_options_build()` actively consumes fields including `optlen` for packet construction. This is stronger than a shallow cleanup dereference, but does not establish controlled reclaim or arbitrary write.

Not awarded:

* Controlled reclaim, arbitrary write, callback control, disclosure, and privilege escalation are not demonstrated.
* Confidentiality and integrity points are not awarded solely because freed storage might be reused.
* No repeated release or refcount signal applies. The stale operation reads the freed options object rather than performing a second free or refcount mutation.
* No extra availability point is awarded for the same possible kernel crash.
* B5-R does not apply because no confirmed retry-accumulated OOB write exists.
* B3-PENDING does not apply because this is not a shared-backing write.
* B4-PENDING does not apply because no authorization decision is bypassed.

3. Reachability analysis

The primary path is reachable by a remote, unauthenticated peer able to send IPv4 SYN packets with options to an exposed TCP listener and retransmit them. It does not require host UID 0, a local account, a capability, namespace creation, request migration, BPF, or a special sysctl.

A listening service must already exist, but that is ordinary service exposure rather than attacker-performed privileged setup. The optional request-migration path requires `tcp_migrate_req=1` or an appropriate BPF reuseport program, but it is not required for the primary vulnerability.

The attacker can repeatedly send SYN traffic, although successful exploitation still requires an inter-CPU overlap between SYNACK construction and child destruction. No special hardware is required. Namespace-scoped privilege is not relevant because the direct trigger requires no local privilege.

4. Primitive and severity interpretation

The exact primitive is an RCU lifetime violation producing a real heap use-after-free. The stale allocation is an active structured IPv4 options object, not fixed asynchronous storage. Its fields are consumed during route and SYNACK packet construction after the owning socket or cloned request has released it.

This is broader than a destructor-only fault because the stale read occurs in active networking processing. It is not a concrete repeated-release case. The first operation frees the options object, but the later operation reads its fields rather than mutating its lifetime or refcount.

The issue is CLASS_B. The demonstrated consequence is invalid post-free access with plausible kernel crash or malformed packet construction. Controlled reclaim, arbitrary kernel read or write, information disclosure, and privilege escalation remain speculative.

ImportantCandidate is YES because this is a directly network-reachable active-object UAF with a concrete broken RCU invariant and nontrivial stale-field consumption. AutoDowngradeAllowed is NO because automatic closure would discard unresolved exploitation leverage in a remotely reachable kernel lifetime corruption primitive. The patch supports Strong Important candidacy for review, but not proven Critical impact.

5. One-sentence report phrase

A remote unauthenticated peer can race IPv4 SYN retransmission against TCP child or request destruction, causing active SYNACK processing to consume freed IP options and potentially crash the kernel.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The vulnerability is a remotely reachable active-object UAF with a confirmed RCU lifetime violation, while the security significance of stale option lengths and possible allocator reuse requires human exploitation-leverage review.

7. Call-site confidence

Call-site confidence: high

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

Patch: ipv4: free inet_opt and ireq_opt after an RCU grace period
Commit: 11a03ce3c4a62d84c10ccdfe47f8075006498568
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=11a03ce3c4a62d84c10ccdfe47f8075006498568

Commit description:

tcp_v4_syn_recv_sock() transfers ownership of ireq->ireq_opt to the
child socket (newinet->inet_opt) without copying it.

Another cpu can concurrently process a retransmitted SYN for the same
request socket, and send a SYNACK from tcp_check_req().
tcp_v4_send_synack() and inet_csk_route_req() read ireq->ireq_opt
under rcu_read_lock() only, and ip_build_and_send_pkt() and
ip_options_build() then read opt->optlen twice.

Note that the SYNACK timer itself is not an issue: it holds a
reference on its request socket, and inet_csk_reqsk_queue_drop()
calls timer_delete_sync() before the child can be freed.

Since commit 079096f ("tcp/dccp: install syn_recv requests
into ehash table"), request sockets are processed without holding
the listener lock, so nothing prevents the child socket from being
freed while the SYNACK is still being built. TCP child sockets do
not have SOCK_RCU_FREE, and inet_sock_destruct() frees inet_opt
with a plain kfree(), leading to a use-after-free in
ip_options_build().

A similar issue exists with request socket migration
(net.ipv4.tcp_migrate_req=1, or a BPF_SK_REUSEPORT_SELECT_OR_MIGRATE
program). reqsk_timer_handler() clones the request socket with
inet_reqsk_clone(), so that the old request socket and its clone
share the same ireq_opt, then reqsk_migrate_reset() clears the
pointer in the old one. Another cpu holding a reference on the old
request socket can still be using these options (sending a SYNACK,
or creating a child in tcp_v4_syn_recv_sock()) when the clone is
freed, and tcp_v4_reqsk_destructor() also uses a plain kfree().

Readers already use RCU, and other paths replacing inet_opt
(do_ip_setsockopt(), cipso_v4_sock_setattr()...) already use
kfree_rcu(). Use kfree_rcu() in inet_sock_destruct() and
tcp_v4_reqsk_destructor() as well.

IPv6 is not affected by the first issue, because tcp_v6_syn_recv_sock()
duplicates the options. tcp_v6_reqsk_destructor() has the same
migration issue with ipv6_opt, which is only set by CALIPSO. This
will be addressed in a separate patch.

Fixes: 079096f ("tcp/dccp: install syn_recv requests into ehash table")
Fixes: c905dee ("tcp: Migrate TCP_NEW_SYN_RECV requests at retransmitting SYN+ACKs.")
Reported-by: Xinyang Ge <xinyang@anthropic.com>
Signed-off-by: Eric Dumazet <edumazet@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20261001221253.2964024-1-edumazet@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv4/af_inet.c
  net/ipv4/tcp_ipv4.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=11a03ce3c4a62d84c10ccdfe47f8075006498568

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

The original Linux kernel CVE announcement for CVE-2026-98432 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98432

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:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 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: 6
  Paranoid ActionableScore: 7

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).