Unusual Encrypting File System Remote call (EFSRPC) to domain controller

Synopsis

Field	Value
Activation Period	14 Days
Training Period	30 Days
Test Period	N/A (single event)
Deduplication Period	1 Day
Required Data	XDR Agent with eXtended Threat Hunting (XTH)
Detection Modules	Identity Analytics
ATT&CK Tactic	Credential Access (TA0006)
ATT&CK Technique	Forced Authentication (T1187), Adversary-in-the-Middle: Name Resolution Poisoning and SMB Relay (T1557.001)
Severity	Low

Description

An unusual Encrypting File System Remote call (EFSRPC) was made to a domain controller.

Attacker's Goals

• An attacker can abuse the Encrypting File System Remote Protocol to coerce authentication from a DC.
• This authentication can later be used for obtaining a DC certificate for DCSync.

Investigative actions

• Check for a suspicious process on the initiator.
• Check if the source host is a vulnerability scanner.
• Check for unusual connections from the server of the requested file location (it may be a relay server).
• Look for unusual AD CS certificate requests.
• Look for following suspicious connections using the DC machine account.
• Check for possible DCSync alerts.

Variations

A suspicious Encrypting File System Remote call (EFSRPC) was made to a domain controller

Synopsis

Field	Value
ATT&CK Tactic	Credential Access (TA0006)
ATT&CK Technique	Forced Authentication (T1187), Adversary-in-the-Middle: Name Resolution Poisoning and SMB Relay (T1557.001)
Severity	Medium

Description

An unusual Encrypting File System Remote call (EFSRPC) was made to a domain controller.

Attacker's Goals

• An attacker can abuse the Encrypting File System Remote Protocol to coerce authentication from a DC.
• This authentication can later be used for obtaining a DC certificate for DCSync.

Investigative actions

• Check for a suspicious process on the initiator.
• Check if the source host is a vulnerability scanner.
• Check for unusual connections from the server of the requested file location (it may be a relay server).
• Look for unusual AD CS certificate requests.
• Look for following suspicious connections using the DC machine account.
• Check for possible DCSync alerts.

Abnormal Encrypting File System Remote call (EFSRPC) to domain controller using EfsRpcFileKeyInfo for the first time

Synopsis

Field	Value
ATT&CK Tactic	Credential Access (TA0006)
ATT&CK Technique	Forced Authentication (T1187), Adversary-in-the-Middle: Name Resolution Poisoning and SMB Relay (T1557.001)
Severity	Low

Description

An abnormal EfsRpcFileKeyInfo Encrypting File System Remote call (EFSRPC) was made to a domain controller for the first time.

Attacker's Goals

• An attacker can abuse the Encrypting File System Remote Protocol to coerce authentication from a DC.
• This authentication can later be used for obtaining a DC certificate for DCSync.

Investigative actions

• Check for a suspicious process on the initiator.
• Check if the source host is a vulnerability scanner.
• Check for unusual connections from the server of the requested file location (it may be a relay server).
• Look for unusual AD CS certificate requests.
• Look for following suspicious connections using the DC machine account.
• Check for possible DCSync alerts.

Abnormal Encrypting File System Remote call (EFSRPC) to domain controller using EfsRpcFileKeyInfo

Synopsis

Field	Value
ATT&CK Tactic	Credential Access (TA0006)
ATT&CK Technique	Forced Authentication (T1187), Adversary-in-the-Middle: Name Resolution Poisoning and SMB Relay (T1557.001)
Severity	Informational

Description

An abnormal EfsRpcFileKeyInfo Encrypting File System Remote call (EFSRPC) was made to a domain controller.

Attacker's Goals

• An attacker can abuse the Encrypting File System Remote Protocol to coerce authentication from a DC.
• This authentication can later be used for obtaining a DC certificate for DCSync.

Investigative actions

• Check for a suspicious process on the initiator.
• Check if the source host is a vulnerability scanner.
• Check for unusual connections from the server of the requested file location (it may be a relay server).
• Look for unusual AD CS certificate requests.
• Look for following suspicious connections using the DC machine account.
• Check for possible DCSync alerts.