[CVE-2026-98251][MODERATE 7.0] openvswitch: avoid reallocating confirmed conntrack labels

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

CVE: CVE-2026-98251
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: openvswitch: avoid reallocating confirmed conntrack labels
Commit: 4371d79ea74407fb992c985b1f94391e35bb8289
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4371d79ea74407fb992c985b1f94391e35bb8289
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98251
Analysis date: Sat, 10 Oct 2026 13:22:18 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98251 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98251

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: 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-2026-98251	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98251 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both 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:H/I:H/A:H';*CWE-416;CWE-362;CWE-663;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'A race in Open vSwitch conntrack label handling can occur when ovs_ct_get_conn_labels adds a labels extension to an already confirmed conntrack. Confirmed conntracks may be read locklessly, while adding the extension can reallocate and free the old extension block as another CPU is still accessing it. This creates a potential use after free condition that can cause a kernel crash and may permit broader memory corruption impact if the freed storage is reused in a controllable way. For the CVSS the PR:N is selected because a remote attacker does not need a local account when existing Open vSwitch rules apply conntrack label operations to attacker controlled traffic. Triggering still requires a suitable Open vSwitch configuration and winning a concurrency window, so AC:H is appropriate. The base assessment uses AV:A because Open vSwitch datapaths are commonly exposed to local, virtual, or data center network segments. The paranoid assessment uses AV:N where traffic from a remote network can reach the affected datapath. Impact is at least denial of service via kernel crash and in the worst defensible case may include confidentiality, integrity, and privilege escalation impact due to the potential use after free.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	SIMPLEFIX HARDWARE LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 4
* Paranoid score: 5
* Conservative floor applied: 3 -> 4 under the real UAF floor because an old extension block can be freed while a concurrent reader is actively accessing it.
* Paranoid floor applied: 4 -> 5 because this is an active runtime object, matching traffic can repeatedly create relevant conntrack activity, and stale consumption occurs in normal conntrack processing rather than cleanup.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF and lifetime violation. Adding a labels extension to a confirmed conntrack can reallocate and free the previous extension block while a lockless reader still accesses that block.
* +1 Realistic kernel crash or strong DoS. Concurrent consumption of freed extension storage can produce an invalid access or corrupted conntrack state.
* No additional Availability point. It would duplicate the same UAF-induced crash consequence.
* Raw conservative total: 2 + 1 = 3.

Paranoid additional signal:

* +1 Attacker-influenced repeatable lifetime manipulation. With an existing Open vSwitch conntrack-label policy, a traffic source can repeatedly generate flows and packet activity that exercise confirmation, label handling, and concurrent lookup. This is technically defensible but depends on policy and call-path details not shown in the one-line diff.
* Raw paranoid total: 2 + 1 + 1 = 4.

Not awarded:

* Remote reachability +2 was not awarded because a suitable Open vSwitch datapath and conntrack-label policy must first be configured by an administrator.
* Strong exploitation leverage +2 was not awarded. Controlled reclaim, attacker-shaped replacement contents, directed writes, callbacks, and arbitrary kernel read or write are not demonstrated.
* Structured stale-object leverage +1 was not separately awarded because the exact fields consumed by concurrent readers and their behavior after reuse are not visible.
* Confidentiality and integrity points were not awarded merely from the possibility that freed storage could be reused.
* No race penalty was applied. The patch establishes concurrency but does not establish a narrow, one-shot, or externally uncontrollable timing window.
* No subsystem-rarity penalty was applied merely because Open vSwitch requires deployment-specific configuration.
* B5-R does not apply. There is no retry-accumulated heap OOB write.
* B3-PENDING does not apply. There is no demonstrated shared-backing or file-backed write.
* B4-PENDING does not apply. No authorization decision changes from DENY to ALLOW.

Repeated-release checks:

* The extension reallocation can end the lifetime of the old extension block.
* A concurrent reader can retain and use a stale reference to that old block.
* There is no demonstrated second put, release, free, or refcount mutation through that exact stale reference.
* Concrete repeated release or refcount +1 was not awarded.
* Paranoid repeated-refcount leverage +1 was withheld.
* FLOOR 5 was not applied through the repeated-release rule. It was applied only to the paranoid score based on below-host-admin active runtime reachability and repeated non-cleanup stale-object consumption.

3. Reachability analysis

The vulnerable allocation occurs only when a confirmed conntrack lacks a labels extension and an Open vSwitch label operation attempts to add one. Open vSwitch and the relevant flow actions require prior administrative configuration, but that does not mean the actor sending subsequent matching traffic needs host-administrator privileges.

With such policy already installed, a remote or adjacent traffic source can potentially create confirmed flows and exercise the configured conntrack-label data path without a host account. Therefore HostAdminRequired is NO and RequiresHostUID0 is NO for the evaluated runtime trigger. The prior setup remains an important deployment prerequisite and prevents awarding the direct remote-reachability bonus.

The supplied code does not establish which user namespace governs all Open vSwitch configuration stages or whether an attacker can create the complete setup inside an attacker-created network namespace. NamespaceScopedPrivilege is therefore UNKNOWN.

No special hardware, firmware, boot option, or unusual execution mode is required. Repeated traffic can provide multiple race attempts, so the race is not shown to be a genuinely one-shot hard race. Exact remote exploitability still depends on flow rules that reach the affected label operation.

4. Primitive and severity interpretation

The exact primitive is an active structured heap lifetime violation. `nf_ct_labels_ext_add()` may reallocate the conntrack extension block and free the old allocation after the conntrack has become visible to lockless readers. Another CPU may continue reading or otherwise consuming the stale extension storage.

This is not fixed stale storage and is not limited to teardown or destructor processing. It affects a live confirmed conntrack during runtime packet processing. It is therefore CLASS_B rather than CLASS_C.

The demonstrated mechanism establishes a real UAF but does not establish controlled reclaim, a chosen replacement object, an arbitrary write, disclosure, callback control, or privilege escalation. A kernel crash and conntrack-state corruption are practical consequences. Broader exploitation remains unresolved rather than demonstrated.

ImportantCandidate is YES because an active runtime UAF involving a freed extension block and concurrent lockless consumption deserves Important-versus-Moderate exploitation review. AutoDowngradeAllowed is NO because automatically reducing it to crash-only Moderate would discard unresolved active-object lifetime leverage. The likely operational severity is Actionable Moderate, with an Important classification possible if call-site analysis demonstrates useful stale-field consumption or attacker-influenced replacement.

5. One-sentence report phrase

A confirmed conntrack labels extension can be reallocated and freed while another CPU accesses it locklessly, creating an active runtime use-after-free that warrants mandatory exploitation-leverage review.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Review the concurrent readers of the conntrack extension block, allocator reuse behavior, exact stale fields consumed, and whether matching traffic can reliably drive reallocation and replacement under deployed Open vSwitch policies.

7. Call-site confidence

Call-site confidence: medium

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

Patch: openvswitch: avoid reallocating confirmed conntrack labels
Commit: 4371d79ea74407fb992c985b1f94391e35bb8289
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4371d79ea74407fb992c985b1f94391e35bb8289

Commit description:

ovs_ct_get_conn_labels() adds the labels extension when a conntrack
entry does not have one.  Confirmed conntracks can be read locklessly,
so adding an extension may reallocate and free the extension block
while another CPU accesses it.

Only add the extension for unconfirmed conntracks.  A confirmed
conntrack without labels now fails the caller's label operation instead
of reallocating its extension storage.

Fixes: c2ac667 ("openvswitch: Allow matching on conntrack label")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Signed-off-by: Zhiling Zou <zhilinz@nebusec.ai>
Reviewed-by: Ilya Maximets <i.maximets@ovn.org>
Reviewed-by: Aaron Conole <aconole@redhat.com>
Link: https://patch.msgid.link/372fbb062b40ae6723684f55484be86ff0064f8e.1789218015.git.zhilinz@nebusec.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/openvswitch/conntrack.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=4371d79ea74407fb992c985b1f94391e35bb8289

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

The original Linux kernel CVE announcement for CVE-2026-98251 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98251

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:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/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: 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).