Remote Management and Monitoring tool - ZohoAssist - File Signature

Hunt Hypothesis

The detection identifies potential adversary use of ZohoAssist, a remote management tool, to establish persistence or command and control channels by leveraging file signature anomalies. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect and mitigate advanced threats exploiting legitimate RMM tools.

KQL Query

let Time_start = now(-5d);
let Time_end = now();
//
// *Will return all binaries signed by Zoho, not just Zoho Assist*
// 
DeviceFileCertificateInfo
| where Timestamp between (Time_start..Time_end)
| where Signer has 'Zoho'
| summarize FirstSeen=min(Timestamp), LastSeen=max(Timestamp), 
    Report=make_set(ReportId), Count=count() by DeviceId, DeviceName

Analytic Rule Definition

id: ba1e02dc-2731-4f65-bdd3-b293e0490e9a
name: Remote Management and Monitoring tool - ZohoAssist - File Signature
description: |
    Remote Monitoring and Management (RMM) programs are IT to manage remote endpoints. Attackers have begun to abuse these programs to persist or provide C2 channels.
    https://github.com/jischell-msft/RemoteManagementMonitoringTools
requiredDataConnectors:
- connectorId: MicrosoftThreatProtection
  dataTypes:
  - DeviceFileCertificateInfo
tactics: CommandAndControl
relevantTechniques: T1219
query: |
  let Time_start = now(-5d);
  let Time_end = now();
  //
  // *Will return all binaries signed by Zoho, not just Zoho Assist*
  // 
  DeviceFileCertificateInfo
  | where Timestamp between (Time_start..Time_end)
  | where Signer has 'Zoho'
  | summarize FirstSeen=min(Timestamp), LastSeen=max(Timestamp), 
      Report=make_set(ReportId), Count=count() by DeviceId, DeviceName

MITRE ATT&CK Context

• Tactic: CommandAndControl
• Technique: T1219 — T1219

References

• [Source Query](https://github.com/Azure/Azure-Sentinel/blob/main/Hunting Queries/Microsoft 365 Defender/RemoteManagementMonitoring/rmm_ZohoAssist_filesig.yaml)

False Positive Guidance

• Scenario: A system administrator is using Zoho Assist to perform remote troubleshooting on a user’s endpoint.
  Filter/Exclusion: Exclude processes initiated from known admin workstations or users with the “IT Admin” group membership.

• Scenario: A scheduled job runs Zoho Assist to push software updates to multiple endpoints during off-peak hours.
  Filter/Exclusion: Exclude processes associated with known update or patch management tools (e.g., Microsoft Endpoint Manager, SCCM) or scheduled tasks with known update scripts.

• Scenario: An IT team uses Zoho Assist to monitor and manage a fleet of virtual machines in a cloud environment (e.g., AWS, Azure).
  Filter/Exclusion: Exclude processes originating from cloud management consoles or virtual machines tagged with “cloud-managed” or “virtualized.”

• Scenario: A user receives a legitimate remote support session from a trusted vendor using Zoho Assist.
  Filter/Exclusion: Exclude connections from known trusted IP ranges or domains associated with authorized support providers.

• Scenario: A security tool or SIEM system uses Zoho Assist to collect logs or metrics from endpoints for monitoring purposes.
  Filter/Exclusion: Exclude processes initiated by known security tools (e.g., Splunk, ELK Stack, or SIEM agents) or with specific log collection permissions.