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We received alarms for this in our SIEM today. I believe it is expected and just "noise". The alarm was triggered immediately after Exchange cleared the ThrottlingConfig.log.

I know Exchange Server 2013 CU5, CU5 includes a Managed Availability probe configuration that is frequently restarting the Microsoft Exchange Shared Cache Service in some environments. The service is being added to provide future performance improvements and is not used in Cumulative Update 5. More information is available in KB2971467

So it looks like this event triggered alarm is a false-positive. Anyone else experience this?

<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>4649</EventID>
        <Version>0</Version>
        <Level>Information</Level>
        <Task>Other Logon/Logoff Events</Task>
        <Opcode>Info</Opcode>
        <Keywords>Audit Failure</Keywords>
        <TimeCreated SystemTime='2018-09-20T20:14:12.793310400Z'/>
        <EventRecordID>79125070</EventRecordID>
        <Correlation/>
        <Execution ProcessID='700' ThreadID='5972'/>
        <Channel>Security</Channel>
        <Computer>DOMAIN</Computer>
        <Security/>
    </System>
    <EventData>A replay attack was detected.

Subject:
    Security ID:        NT AUTHORITY\SYSTEM
    Account Name:       SERVERNAME$
    Account Domain:     DOMAIN
    Logon ID:       0x3E7

Credentials Which Were Replayed:
    Account Name:       HealthMailboxXXXXX
    Account Domain:     DOMAIN

Process Information:
    Process ID:     0x673b81d620
    Process Name:       C:\Windows\System32\inetsrv\w3wp.exe

Network Information:
    Workstation Name:   -

Detailed Authentication Information:
    Request Type:       KRB_AP_REQ
    Logon Process:      Kerberos
    Authentication Package: Kerberos
    Transited Services: -

This event indicates that a Kerberos replay attack was detected- a request was received twice with identical information. This condition could be caused by network misconfiguration.</EventData>
</Event>

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One item to check is whether or not a result is false positive. The final portion of the log states a caution of the results:

This event indicates that a Kerberos replay attack was detected
- a request was received twice with identical information.
This condition could be caused by network misconfiguration.

Microsoft help docs at https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4649 also recommend doing a manual investigation as part of checking to see if this is a false positive.

I've done scans that have ended up with false positive and needed additional checks.

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