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I am running into an issue with traffic from a webapp server to a database server being blocked or filtered. I have allowed inbound and outbound traffic on the needed ip and port with a firewall rule, but some packets/connections are still being blocked/dropped.

In the event log for the most recent occurrence I see:

The Windows Filtering Platform has blocked a packet.

Application Information:
    Process ID:        0
    Application Name:    -

Network Information:
    Direction:        Inbound
    Source Address:        redacted-webapp-ip
    Source Port:        51888
    Destination Address:    redacted-database-ip
    Destination Port:        1433
    Protocol:        6

Filter Information:
    Filter Run-Time ID:    72605
    Layer Name:        Transport
    Layer Run-Time ID:    13

With the output from netsh wfp show state I can find this information about the filter that caused the drop:

<item>
    <filterKey>{ccea04a9-00af-48c8-ba5e-ceba7bfc75ae}</filterKey>
    <displayData>
        <name>Port Scanning Prevention Filter</name>
        <description>This filter prevents port scanning.</description>
    </displayData>
    <flags/>
    <providerKey>{decc16ca-3f33-4346-be1e-8fb4ae0f3d62}</providerKey>
    <providerData>
        <data>ffffffffffffffff</data>
        <asString>........</asString>
    </providerData>
    <layerKey>FWPM_LAYER_INBOUND_TRANSPORT_V4_DISCARD</layerKey>
    <subLayerKey>{b3cdd441-af90-41ba-a745-7c6008ff2301}</subLayerKey>
    <weight>
        <type>FWP_UINT8</type>
        <uint8>12</uint8>
    </weight>
    <filterCondition numItems="1">
        <item>
            <fieldKey>FWPM_CONDITION_FLAGS</fieldKey>
            <matchType>FWP_MATCH_FLAGS_NONE_SET</matchType>
            <conditionValue>
                <type>FWP_UINT32</type>
                <uint32>3</uint32>
            </conditionValue>
        </item>
    </filterCondition>
    <action>
        <type>FWP_ACTION_CALLOUT_TERMINATING</type>
        <calloutKey>FWPM_CALLOUT_WFP_TRANSPORT_LAYER_V4_SILENT_DROP</calloutKey>
    </action>
    <rawContext>0</rawContext>
    <reserved/>
    <filterId>72605</filterId>
    <effectiveWeight>
        <type>FWP_UINT64</type>
        <uint64>13835058055315718144</uint64>
    </effectiveWeight>
</item>

Can anyone point me in the right direction on determining the cause of this? Any way to tell what is adding/has added this filter?

No antivirus software was installed and I couldn't locate any other software that looked suspect. In addition to the "Port Scanning Prevention Filter" I have also seen one named "Query User" (causing similar issues) which I cannot track down the origin of either. (Other legitimate traffic outside of this example is periodically being blocked by these types of filters too.)

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