sigma-rules/rules/windows/execution_ms_office_written_file.toml

[metadata]
creation_date = "2020/09/02"
integration = ["endpoint"]
maturity = "production"
updated_date = "2024/08/06"

[rule]
author = ["Elastic"]
description = """
Identifies an executable created by a Microsoft Office application and subsequently executed. These processes are often
launched via scripts inside documents or during exploitation of Microsoft Office applications.
"""
from = "now-120m"
index = ["logs-endpoint.events.process-*", "logs-endpoint.events.file-*", "endgame-*"]
interval = "60m"
language = "eql"
license = "Elastic License v2"
name = "Execution of File Written or Modified by Microsoft Office"
note = """## Triage and analysis

### Investigating Execution of File Written or Modified by Microsoft Office

Microsoft Office, a widely used suite of productivity applications, is frequently targeted by attackers due to its popularity in corporate environments. Attackers exploit its extensive capabilities, like macro scripts in Word and Excel, to gain initial access to systems. They often use Office documents as delivery mechanisms for malware or phishing attempts, taking advantage of their trusted status in professional settings.

This rule searches for executable files written by MS Office applications executed in sequence. This is most likely the result of the execution of malicious documents or exploitation for initial access or privilege escalation. This rule can also detect suspicious processes masquerading as the MS Office applications.

#### Possible investigation steps

- Investigate the process execution chain (parent process tree) for unknown processes. Examine their executable files for prevalence, whether they are located in expected locations, and if they are signed with valid digital signatures.
- Investigate other alerts associated with the user/host during the past 48 hours.
- Retrieve MS Office documents received and opened by the user that could cause this behavior. Common locations include, but are not limited to, the Downloads and Document folders and the folder configured at the email client.
- Determine if the collected files are malicious:
  - Use a private sandboxed malware analysis system to perform analysis.
    - Observe and collect information about the following activities:
      - Attempts to contact external domains and addresses.
      - File and registry access, modification, and creation activities.
      - Service creation and launch activities.
      - Scheduled task creation.
  - Use the PowerShell `Get-FileHash` cmdlet to get the files' SHA-256 hash values.
    - Search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.

### False positive analysis

- This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.

### Response and remediation

- Initiate the incident response process based on the outcome of the triage.
- Isolate the involved host to prevent further post-compromise behavior.
- Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business systems, and web services.
- If the triage identified malware, search the environment for additional compromised hosts.
  - Implement temporary network rules, procedures, and segmentation to contain the malware.
  - Stop suspicious processes.
  - Immediately block the identified indicators of compromise (IoCs).
  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
- Remove and block malicious artifacts identified during triage.
- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
  - If the malicious file was delivered via phishing:
    - Block the email sender from sending future emails.
    - Block the malicious web pages.
    - Remove emails from the sender from mailboxes.
    - Consider improvements to the security awareness program.
- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the mean time to respond (MTTR).
"""
risk_score = 73
rule_id = "0d8ad79f-9025-45d8-80c1-4f0cd3c5e8e5"
severity = "high"
tags = [
    "Domain: Endpoint",
    "OS: Windows",
    "Use Case: Threat Detection",
    "Tactic: Execution",
    "Resources: Investigation Guide",
    "Data Source: Elastic Endgame",
    "Data Source: Elastic Defend",
]
type = "eql"

query = '''
sequence with maxspan=2h
  [file where host.os.type == "windows" and event.type != "deletion" and file.extension : "exe" and
     (process.name : "WINWORD.EXE" or
      process.name : "EXCEL.EXE" or
      process.name : "OUTLOOK.EXE" or
      process.name : "POWERPNT.EXE" or
      process.name : "eqnedt32.exe" or
      process.name : "fltldr.exe" or
      process.name : "MSPUB.EXE" or
      process.name : "MSACCESS.EXE")
  ] by host.id, file.path
  [process where host.os.type == "windows" and event.type == "start" and 
   not (process.name : "NewOutlookInstaller.exe" and process.code_signature.subject_name : "Microsoft Corporation" and process.code_signature.trusted == true) and 
   not (process.name : "ShareFileForOutlook-v*.exe" and process.code_signature.subject_name : "Citrix Systems, Inc." and process.code_signature.trusted == true)
  ] by host.id, process.executable
'''


[[rule.threat]]
framework = "MITRE ATT&CK"

[rule.threat.tactic]
id = "TA0002"
name = "Execution"
reference = "https://attack.mitre.org/tactics/TA0002/"
[[rule.threat]]
framework = "MITRE ATT&CK"
[[rule.threat.technique]]
id = "T1566"
name = "Phishing"
reference = "https://attack.mitre.org/techniques/T1566/"
[[rule.threat.technique.subtechnique]]
id = "T1566.001"
name = "Spearphishing Attachment"
reference = "https://attack.mitre.org/techniques/T1566/001/"

[[rule.threat.technique.subtechnique]]
id = "T1566.002"
name = "Spearphishing Link"
reference = "https://attack.mitre.org/techniques/T1566/002/"



[rule.threat.tactic]
id = "TA0001"
name = "Initial Access"
reference = "https://attack.mitre.org/tactics/TA0001/"