The Windows Filtering Platform has blocked a connection

// EVENT DEFINITION:

A network connection attempt was blocked by Windows Filtering Platform or host firewall rules.

// DETAILED TELEMETRY & CONTEXT:

Event ID 5157 records network connection block events (`Application Name`, `Direction: Inbound / Outbound`, `Source/Dest IP & Port`, `Filter ID`). High volumes of `5157` inbound blocks indicate active port scanning (`T1046`), while outbound blocks indicating unauthorized processes (`powershell.exe`, `curl.exe`, malware droppers) attempting to connect to blocked command-and-control servers or disallowed ports.

[ ! ]Failure Reason / Root Cause Analysis

Network connection attempt dropped by WFP filter rule (`Filter Run-Time ID`).

Operational Metadata & Applicability

Log Category:Windows Firewall

Audit Type Classification:Failure Audit

Supported Operating Systems:Windows Server 2016, 2019, 2022 / Windows Client 10, 11 (Enterprise / Pro)

Threat Hunting Keywords:

5157wfp blocked connectionfirewall blocked connectionport scan blockedc2 connection blockedoutbound block

MITRE ATT&CK Framework Alignment

T1071

Application Layer ProtocolTactic: Command and Control

T1046

Network Service DiscoveryTactic: Discovery

Mitigation Playbook & Recommended SOC Actions

•Inspect `Application Name` and `Destination Address` for outbound blocks. If a local application repeatedly attempts connections to external IP addresses on non-standard ports, investigate the endpoint for beaconing malware.

Representative Windows Event XML Schema

<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-Security-Auditing" Guid="{54849625-5478-4994-A5BA-3E3B0328C30D}" />
    <EventID>5157</EventID>
    <Version>0</Version>
    <Level>0</Level>
    <Task>12544</Task>
    <Opcode>0</Opcode>
    <Keywords>0x8020000000000000</Keywords>
    <TimeCreated SystemTime="2026-07-17T09:54:44.361Z" />
    <EventRecordID>1048576</EventRecordID>
    <Correlation />
    <Execution ProcessID="612" ThreadID="1024" />
    <Channel>Security</Channel>
    <Computer>DC01.enterprise.internal</Computer>
    <Security />
  </System>
  <EventData>
    <Data Name="SubjectUserSid">S-1-5-18</Data>
    <Data Name="SubjectUserName">SYSTEM</Data>
    <Data Name="SubjectDomainName">NT AUTHORITY</Data>
    <Data Name="SubjectLogonId">0x3e7</Data>
    <!-- Event telemetry fields specific to The Windows Filtering Platform has blocked a connection -->
  </EventData>
</Event>

Correlated / Related Security Event IDs

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