Exchange Server RPC request high

Rule ID

PH_Rule_Mail_3

Default Status

Disabled

Description

Detects a spike in MS Exchange server RPC requests

Severity

MITRE ATT&CK® Tactics

Impact

Impact consists of techniques that adversaries use to disrupt availability or compromise integrity by manipulating business and operational processes. Techniques used for impact can include destroying or tampering with data. In some cases, business processes can look fine, but may have been altered to benefit the adversaries’ goals. These techniques might be used by adversaries to follow through on their end goal or to provide cover for a confidentiality breach.

https://attack.mitre.org/tactics/TA0040

MITRE ATT&CK® Techniques

T1499.002

Endpoint Denial of Service: Service Exhaustion Flood

Adversaries may target the different network services provided by systems to conduct a DoS. Adversaries often target DNS and web services, however others have been targeted as well. One example of this type of attack is known as a simple HTTP flood, where an adversary sends a large number of HTTP requests to a web server to overwhelm it and/or an application that runs on top of it. Another variation, known as a SSL renegotiation attack, the adversary establishes a SSL/TLS connection and then proceeds to make a series of renegotiation requests. Because the cryptographic renegotiation has a meaningful cost in computation cycles, this can cause an impact to the availability of the service when done in volume.

https://attack.mitre.org/techniques/T1499/002

Impacts

Application

Data Source

MS Exchange monitoring via OMI or FortiSIEM Agent

Detection

Correlation

Remediation Guidance

Identify the root cause of the performance issue and allocate more resources if needed.

Time Window

If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.

300 seconds

Trigger Conditions

If the following defined pattern/s occur within a 300 second time window.

RPCHigh

SubPattern Definitions

SubPattern Name: RPCHigh

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

eventType = "PH_DEV_MON_APP_MSEXCH_MET"

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID

hostName

Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

COUNT (*) >= 2 AND AVG(exchRPCReq) >= 30

Incident Attribute Mapping

This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.

The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern

 hostName = RPCHigh.hostName,
 exchRPCReq = RPCHigh.AVG(exchRPCReq)

FortiSIEM Rules