Suspicious MS Outlook Child Process

Identifies suspicious child processes of Microsoft Outlook. These child processes are often associated with spear phishing activity.

Elastic rule (View on GitHub)

  1[metadata]
  2creation_date = "2020/02/18"
  3integration = ["endpoint", "windows", "system", "sentinel_one_cloud_funnel"]
  4maturity = "production"
  5min_stack_comments = "SentinelOne integration package minimum version for validation."
  6min_stack_version = "8.11.0"
  7updated_date = "2024/05/16"
  8
  9[rule]
 10author = ["Elastic"]
 11description = """
 12Identifies suspicious child processes of Microsoft Outlook. These child processes are often associated with spear
 13phishing activity.
 14"""
 15from = "now-9m"
 16index = ["winlogbeat-*", "logs-endpoint.events.process-*", "logs-windows.*", "endgame-*", "logs-system.security*", "logs-sentinel_one_cloud_funnel.*"]
 17language = "eql"
 18license = "Elastic License v2"
 19name = "Suspicious MS Outlook Child Process"
 20note = """## Triage and analysis
 21
 22### Investigating Suspicious MS Outlook Child Process
 23
 24Microsoft Outlook is an email client that provides contact, email calendar, and task management features. Outlook is widely used, either standalone or as part of the Office suite.
 25
 26This rule looks for suspicious processes spawned by MS Outlook, which can be the result of the execution of malicious documents and/or exploitation for initial access.
 27
 28#### Possible investigation steps
 29
 30- 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.
 31- Investigate other alerts associated with the user/host during the past 48 hours.
 32- Retrieve recently opened files received via email 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.
 33- Determine if the collected files are malicious:
 34  - Use a private sandboxed malware analysis system to perform analysis.
 35    - Observe and collect information about the following activities:
 36      - Attempts to contact external domains and addresses.
 37      - File and registry access, modification, and creation activities.
 38      - Service creation and launch activities.
 39      - Scheduled task creation.
 40  - Use the PowerShell Get-FileHash cmdlet to get the files' SHA-256 hash values.
 41    - Search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
 42
 43### False positive analysis
 44
 45- This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.
 46
 47### Response and remediation
 48
 49- Initiate the incident response process based on the outcome of the triage.
 50- Isolate the involved host to prevent further post-compromise behavior.
 51- 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.
 52- If the triage identified malware, search the environment for additional compromised hosts.
 53  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 54  - Stop suspicious processes.
 55  - Immediately block the identified indicators of compromise (IoCs).
 56  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 57- Remove and block malicious artifacts identified during triage.
 58- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
 59- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 60  - If the malicious file was delivered via phishing:
 61    - Block the email sender from sending future emails.
 62    - Block the malicious web pages.
 63    - Remove emails from the sender from mailboxes.
 64    - Consider improvements to the security awareness program.
 65- 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).
 66"""
 67risk_score = 21
 68rule_id = "32f4675e-6c49-4ace-80f9-97c9259dca2e"
 69setup = """## Setup
 70
 71If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2,
 72events will not define `event.ingested` and default fallback for EQL rules was not added until version 8.2.
 73Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate
 74`event.ingested` to @timestamp.
 75For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html
 76"""
 77severity = "low"
 78tags = ["Domain: Endpoint", "OS: Windows", "Use Case: Threat Detection", "Tactic: Initial Access", "Tactic: Defense Evasion", "Tactic: Execution", "Resources: Investigation Guide", "Data Source: Elastic Endgame", "Data Source: Elastic Defend", "Data Source: SentinelOne"]
 79timestamp_override = "event.ingested"
 80type = "eql"
 81
 82query = '''
 83process where host.os.type == "windows" and event.type == "start" and
 84  process.parent.name : "outlook.exe" and
 85  process.name : ("Microsoft.Workflow.Compiler.exe", "arp.exe", "atbroker.exe", "bginfo.exe", "bitsadmin.exe",
 86                  "cdb.exe", "certutil.exe", "cmd.exe", "cmstp.exe", "cscript.exe", "csi.exe", "dnx.exe", "dsget.exe",
 87                  "dsquery.exe", "forfiles.exe", "fsi.exe", "ftp.exe", "gpresult.exe", "hostname.exe", "ieexec.exe",
 88                  "iexpress.exe", "installutil.exe", "ipconfig.exe", "mshta.exe", "msxsl.exe", "nbtstat.exe", "net.exe",
 89                  "net1.exe", "netsh.exe", "netstat.exe", "nltest.exe", "odbcconf.exe", "ping.exe", "powershell.exe",
 90                  "pwsh.exe", "qprocess.exe", "quser.exe", "qwinsta.exe", "rcsi.exe", "reg.exe", "regasm.exe",
 91                  "regsvcs.exe", "regsvr32.exe", "sc.exe", "schtasks.exe", "systeminfo.exe", "tasklist.exe",
 92                  "tracert.exe", "whoami.exe", "wmic.exe", "wscript.exe", "xwizard.exe")
 93'''
 94
 95
 96[[rule.threat]]
 97framework = "MITRE ATT&CK"
 98[[rule.threat.technique]]
 99id = "T1566"
100name = "Phishing"
101reference = "https://attack.mitre.org/techniques/T1566/"
102[[rule.threat.technique.subtechnique]]
103id = "T1566.001"
104name = "Spearphishing Attachment"
105reference = "https://attack.mitre.org/techniques/T1566/001/"
106
107
108
109[rule.threat.tactic]
110id = "TA0001"
111name = "Initial Access"
112reference = "https://attack.mitre.org/tactics/TA0001/"
113
114[[rule.threat]]
115framework = "MITRE ATT&CK"
116[[rule.threat.technique]]
117id = "T1059"
118name = "Command and Scripting Interpreter"
119reference = "https://attack.mitre.org/techniques/T1059/"
120[[rule.threat.technique.subtechnique]]
121id = "T1059.001"
122name = "PowerShell"
123reference = "https://attack.mitre.org/techniques/T1059/001/"
124
125[[rule.threat.technique.subtechnique]]
126id = "T1059.003"
127name = "Windows Command Shell"
128reference = "https://attack.mitre.org/techniques/T1059/003/"
129
130
131
132[rule.threat.tactic]
133id = "TA0002"
134name = "Execution"
135reference = "https://attack.mitre.org/tactics/TA0002/"
136
137[[rule.threat]]
138framework = "MITRE ATT&CK"
139[[rule.threat.technique]]
140id = "T1218"
141name = "System Binary Proxy Execution"
142reference = "https://attack.mitre.org/techniques/T1218/"
143
144
145
146[rule.threat.tactic]
147id = "TA0005"
148name = "Defense Evasion"
149reference = "https://attack.mitre.org/tactics/TA0005/"

Triage and analysis

Investigating Suspicious MS Outlook Child Process

Microsoft Outlook is an email client that provides contact, email calendar, and task management features. Outlook is widely used, either standalone or as part of the Office suite.

This rule looks for suspicious processes spawned by MS Outlook, which can be the result of the execution of malicious documents and/or exploitation for initial access.

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 recently opened files received via email 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).

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