[CVE-2026-97611][MODERATE 7.0] net: openvswitch: fix use-after-free of the flow table mask array

[CVE-2026-97611][MODERATE 7.0] net: openvswitch: fix use-after-free of the flow table mask array

[AL-KERNEL]

CVE: CVE-2026-97611
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net: openvswitch: fix use-after-free of the flow table mask array
Commit: cd982e11684def5d4a9fcfd5354de09032828414
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cd982e11684def5d4a9fcfd5354de09032828414
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97611
Analysis date: Fri, 25 Sep 2026 14:51:18 -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.

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

The original Linux kernel CVE announcement for CVE-2026-97611 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97611

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.

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

CVE-2026-97611	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97611 CHECK WITH IMPACT FROM ORIG NN 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:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use after free in the Open vSwitch flow table mask array can occur because tbl_mask_array_realloc() schedules the old array for RCU freeing before publishing the replacement array. A packet lookup entering ovs_flow_tbl_lookup_stats during this preemptible window can acquire the old array after call_rcu has started its grace period. The old array can then be freed while flow_lookup still dereferences it, resulting in a kernel use after free and at least a local denial of service. For the CVSS the PR:L is selected because reliable triggering normally requires the ability to modify Open vSwitch datapath flows or otherwise induce mask array reallocation, which commonly requires CAP_NET_ADMIN or delegated Open vSwitch administration. Packet processing can be influenced by network traffic, but remote traffic alone does not reliably trigger the reallocation race. The confirmed kernel heap UAF creates a plausible worst case risk of confidentiality integrity and privilege impact and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	READ DANGER UAF LINUS  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* Conservative floor applied: 3 -> 4 under the Real UAF FLOOR 4 rule.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative signals:

* +2 Real UAF / active lifetime violation. `tbl_mask_array_realloc()` schedules `old` for RCU freeing while `tbl->mask_array` still exposes `old` to new RCU readers. The supplied KASAN trace confirms a post-free read in `flow_lookup()`.
* +1 Reliable kernel crash / strong DoS concern. The stale object is dereferenced in the Open vSwitch packet lookup path. The demonstrated KASAN slab use-after-free can realistically result in an Oops or kernel crash without KASAN.
* No host-admin penalty. The supplied evidence does not prove that the full trigger requires host-admin-equivalent authority.
* No hard-race penalty. Although this is an RCU ordering race, the vulnerable interval executes in preemptible process context and the commit explicitly states it can outlast the RCU grace period. The supplied PoC trace establishes that the race is reachable.

Conservative raw score: 2 + 1 = 3.

Conservative floor:

* FLOOR 4 applies. This is not fixed stale DMA storage or a shallow destructor-only dereference. A freed active flow-table mask array is consumed by normal packet lookup processing. Host-admin-equivalent privilege is not positively established.

Paranoid-only signals:

* +1 Structured stale-object exploitation leverage. The stale `mask_array` is an active structured lookup object. Open vSwitch flow-table management can influence the array contents and size, while the later stale use occurs in `flow_lookup()` during packet processing. This supports further manual analysis of stale mask entry consumption, but does not establish controlled reclaim or arbitrary read/write.

Paranoid raw score: 2 + 1 + 1 = 4.

Paranoid floor:

* FLOOR 4 is already met. The recommended paranoid score is increased to 5 because the active structured packet-processing use leaves meaningful exploitation leverage unresolved.

Important non-awarded signals:

* Controlled reclaim or attacker-controlled replacement of the freed slab object is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated.
* Callback, function-pointer, credential, or refcount takeover is not demonstrated.
* Direct remote reachability is not established. Packet traffic can reach the reader, but the attacker must also reliably induce flow-table mask-array reallocation.
* No concrete repeated release, put, free, or refcount mutation through the same dangling reference exists.
* No confidentiality or integrity point is awarded merely because a heap UAF could theoretically be exploited after allocator reuse.
* No additional availability point is awarded because the same UAF crash mechanism is already counted as the DoS signal.

3. Reachability analysis

The reader side is reached through ordinary Open vSwitch packet processing:

`ovs_vport_receive() -> ovs_dp_process_packet() -> ovs_flow_tbl_lookup_stats() -> flow_lookup()`.

The writer side is `tbl_mask_array_realloc()`, which is associated with flow-table mask-array resizing and therefore requires a flow-table update or another operation that changes relevant Open vSwitch datapath state. The supplied patch does not include the full netlink or control-plane call chain for this operation.

A remote peer can influence packet arrival and therefore trigger the reader path. However, remote packet traffic alone does not establish the complete trigger because it does not by itself prove control over the flow-table update that invokes `tbl_mask_array_realloc()`.

A local or delegated Open vSwitch control-plane actor with authority to alter datapath flows is the most relevant attacker model. Such authority may be based on CAP_NET_ADMIN or access to an Open vSwitch management service, but the supplied evidence does not establish whether all required operations can be completed inside an attacker-controlled network namespace.

Therefore:

* HostAdminRequired is UNKNOWN. Host-admin-equivalent authority is not proven, but below-host-admin completion of the entire sequence is also not proven.
* NamespaceScopedPrivilege is UNKNOWN. Open vSwitch uses network namespaces, but the supplied evidence does not establish that all required datapath creation, flow update, reallocation, and packet injection stages are available to an attacker in a non-host namespace.
* No prior special hardware, firmware, boot option, or sysctl prerequisite is indicated.
* The race is plausibly repeatable for an actor able to repeatedly update flow state and inject or generate matching packet traffic. The supplied PoC confirms reachability but does not provide a full repeatability analysis.

4. Primitive and severity interpretation

The exact primitive is an RCU lifetime-ordering violation. The old flow-table mask array is retired with `call_rcu()` before the new array is published. A new RCU reader can therefore acquire the old pointer after the grace period has started. The RCU callback can free the array before that reader finishes `flow_lookup()`.

This is an active structured-object UAF, not fixed stale storage and not merely a cleanup or destructor path. The stale object is a flow lookup mask array used in normal Open vSwitch packet processing. The supplied trace shows an actual post-free read of that array in `flow_lookup()`.

There is no concrete second release, `put()`, refcount decrement, or other lifetime-mutating operation through the dangling pointer. The vulnerability is therefore not a repeated-release or double-free case.

The demonstrated consequence is a kernel slab use-after-free and realistic local denial of service. A stronger consequence remains speculative. The patch does not demonstrate controlled replacement of the freed array, attacker-controlled reuse of its slab address, arbitrary kernel read/write, function-pointer use, information disclosure, privilege escalation, or a security-boundary bypass.

PrimitiveClass is CLASS_B because a concrete active-object kernel UAF exists. ImportantCandidate is YES because stale structured data is consumed during packet lookup and the practical leverage of attacker-influenced flow-table state requires manual analysis. AutoDowngradeAllowed is NO because automatically treating this as an ordinary crash-only issue would discard a confirmed active RCU UAF in a packet-processing path before evaluating flow-control permissions, allocator reuse conditions, and reachable Open vSwitch deployment models.

Likely operational severity is Actionable Moderate at minimum. It is not a demonstrated privilege-escalation vulnerability, but it is a confirmed kernel heap lifetime violation with unresolved exploitation potential.

5. One-sentence report phrase

An RCU ordering flaw in Open vSwitch can free a flow-table mask array while packet lookup still dereferences it, causing a kernel use-after-free and potential denial of service, with further exploitation impact requiring manual review.

6. Manual review recommendation

MANUAL CHECK REQUIRED

A confirmed active structured RCU UAF is reached from the packet-processing path, while the complete flow-table control-plane privilege model and potential stale-object reuse leverage are not resolved by the patch alone.

7. Call-site confidence

Call-site confidence: medium

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

Patch: net: openvswitch: fix use-after-free of the flow table mask array
Commit: cd982e11684def5d4a9fcfd5354de09032828414
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cd982e11684def5d4a9fcfd5354de09032828414

Commit description:

tbl_mask_array_realloc() retires the old mask_array before it stops being
reachable:

	old = ovsl_dereference(tbl->mask_array);
	if (old) {
		...
		call_rcu(&old->rcu, mask_array_rcu_cb);
	}

	rcu_assign_pointer(tbl->mask_array, new);

call_rcu() only waits for read-side critical sections already in flight.
tbl->mask_array still points at old between the call_rcu() and the
rcu_assign_pointer(), so a reader entering ovs_flow_tbl_lookup_stats() in
that window picks up old in a fresh critical section that the pending
grace period does not cover.

tbl_mask_array_realloc() runs in process context under ovs_mutex, so the
window is preemptible and can outlast the grace period. Then
mask_array_rcu_cb() frees old before the swap runs:

  BUG: KASAN: slab-use-after-free in flow_lookup.constprop.0+0x2bf/0x2f0
  Read of size 8 at addr ffff888020b3e018 by task poc/741
   flow_lookup.constprop.0+0x2bf/0x2f0
   ovs_flow_tbl_lookup_stats+0x4a3/0x5c0
   ovs_dp_process_packet+0x19c/0x710
   ovs_vport_receive+0x243/0x390
   internal_dev_xmit+0x81/0x170
  Freed by task 728:
   kfree+0x16a/0x4e0
   rcu_core+0x853/0x1030

Publish the new array before retiring the old one. The kfree_rcu() that
call_rcu() replaced ran after the swap.

Fixes: eac87c4 ("net: openvswitch: reorder masks array based on usage")
Cc: stable@vger.kernel.org
Signed-off-by: Norbert Szetei <norbert@doyensec.com>
Reviewed-by: Ilya Maximets <i.maximets@ovn.org>
Acked-by: Eelco Chaudron echaudro@redhat.com
Link: https://patch.msgid.link/DE115F9C-2545-423E-A702-986FC952FD62@doyensec.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/openvswitch/flow_table.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=cd982e11684def5d4a9fcfd5354de09032828414

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

The original Linux kernel CVE announcement for CVE-2026-97611 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97611

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