User deleted from Remote Desktop User Group

Rule ID

PH_Rule_Change_3E

Default Status

Enabled

Description

Detects users deleted from remote desktop user group

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

T1531

Account Access Removal

Adversaries may interrupt availability of system and network resources by inhibiting access to accounts utilized by legitimate users. Accounts may be deleted, locked, or manipulated (ex: changed credentials) to remove access to accounts.

https://attack.mitre.org/techniques/T1531

Impacts

Application

Data Source

Windows Security Log via OMI or FortiSIEM Agent

Detection

Correlation

Remediation Guidance

Make sure it is an authorized change

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.

DCUserGrpChange

SubPattern Definitions

SubPattern Name: DCUserGrpChange

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

reptDevIpAddr IN (Group@PH_SYS_DEVICE_WINDOWS_SERVER)  AND eventType IN (Group@PH_SYS_EVENT_GroupMemberRemoved) AND targetUserGrp = "Remote Desktop Users"

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

reptDevName,user,computer,domain,targetUser,targetUserGrp,targetDomain

Aggregate Constraint

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

COUNT(*) >= 1

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 = DCUserGrpChange.reptDevName,
 user = DCUserGrpChange.user,
 computer = DCUserGrpChange.computer,
 domain = DCUserGrpChange.domain,
 targetUser = DCUserGrpChange.targetUser,
 targetDomain = DCUserGrpChange.targetDomain,
targetUserGrp = DCUserGrpChange.targetUserGrp

FortiSIEM Rules