Suspicious MS Outlook Child Process

  1[metadata]
  2creation_date = "2020/02/18"
  3integration = ["endpoint", "windows", "system", "sentinel_one_cloud_funnel", "m365_defender", "crowdstrike"]
  4maturity = "production"
  5updated_date = "2026/09/18"
  6
  7[rule]
  8author = ["Elastic"]
  9description = """
 10Identifies suspicious child processes of Microsoft Outlook. These child processes are often associated with spear
 11phishing activity.
 12"""
 13from = "now-9m"
 14index = [
 15    "endgame-*",
 16    "logs-crowdstrike.fdr*",
 17    "logs-endpoint.events.process-*",
 18    "logs-m365_defender.event-*",
 19    "logs-sentinel_one_cloud_funnel.*",
 20    "logs-system.security*",
 21    "logs-windows.forwarded*",
 22    "logs-windows.sysmon_operational-*",
 23    "winlogbeat-*",
 24]
 25language = "eql"
 26license = "Elastic License v2"
 27name = "Suspicious MS Outlook Child Process"
 28note = """## Triage and analysis
 29
 30### Investigating Suspicious MS Outlook Child Process
 31
 32Microsoft 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.
 33
 34This 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.
 35
 36#### Possible investigation steps
 37
 38- 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.
 39- Investigate other alerts associated with the user/host during the past 48 hours.
 40- 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.
 41- Determine if the collected files are malicious:
 42  - Use a private sandboxed malware analysis system to perform analysis.
 43    - Observe and collect information about the following activities:
 44      - Attempts to contact external domains and addresses.
 45      - File and registry access, modification, and creation activities.
 46      - Service creation and launch activities.
 47      - Scheduled task creation.
 48  - Use the PowerShell Get-FileHash cmdlet to get the files' SHA-256 hash values.
 49    - Search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
 50
 51### False positive analysis
 52
 53- This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.
 54
 55### Response and remediation
 56
 57- Initiate the incident response process based on the outcome of the triage.
 58- Isolate the involved host to prevent further post-compromise behavior.
 59- 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.
 60- If the triage identified malware, search the environment for additional compromised hosts.
 61  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 62  - Stop suspicious processes.
 63  - Immediately block the identified indicators of compromise (IoCs).
 64  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 65- Remove and block malicious artifacts identified during triage.
 66- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
 67- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 68  - If the malicious file was delivered via phishing:
 69    - Block the email sender from sending future emails.
 70    - Block the malicious web pages.
 71    - Remove emails from the sender from mailboxes.
 72    - Consider improvements to the security awareness program.
 73- 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).
 74"""
 75
 76setup = """## Setup
 77
 78This rule is designed for data generated by [Elastic Defend](https://www.elastic.co/security/endpoint-security), which provides native endpoint detection and response, along with event enrichments designed to work with our detection rules.
 79
 80Setup instructions: https://ela.st/install-elastic-defend
 81
 82### Additional data sources
 83
 84This rule also supports the following third-party data sources. For setup instructions, refer to the links below:
 85
 86- [CrowdStrike](https://ela.st/crowdstrike-integration)
 87- [Microsoft Defender XDR](https://ela.st/m365-defender)
 88- [SentinelOne Cloud Funnel](https://ela.st/sentinel-one-cloud-funnel)
 89- [Sysmon Event ID 1 - Process Creation](https://ela.st/sysmon-event-1-setup)
 90- [Windows Process Creation Logs](https://ela.st/audit-process-creation)
 91"""
 92
 93risk_score = 21
 94rule_id = "32f4675e-6c49-4ace-80f9-97c9259dca2e"
 95severity = "low"
 96tags = [
 97    "Domain: Endpoint",
 98    "OS: Windows",
 99    "Use Case: Threat Detection",
100    "Tactic: Initial Access",
101    "Tactic: Defense Evasion",
102    "Tactic: Execution",
103    "Resources: Investigation Guide",
104    "Data Source: Elastic Endgame",
105    "Data Source: Elastic Defend",
106    "Data Source: SentinelOne",
107    "Data Source: Microsoft Defender XDR",
108    "Data Source: Windows Security Event Logs",
109    "Data Source: Crowdstrike",
110    "Data Source: Sysmon",
111    "Noise: Medium",
112    "Performance: Normal",
113    "Threat: Living off the Land",
114    "Rule Type: Event Correlation (EQL)",
115    "Platform: Windows",
116]
117timestamp_override = "event.ingested"
118type = "eql"
119
120query = '''
121process where host.os.type == "windows" and event.type == "start" and
122  process.parent.name : "outlook.exe" and
123  process.name : ("Microsoft.Workflow.Compiler.exe", "arp.exe", "atbroker.exe", "bginfo.exe", "bitsadmin.exe",
124                  "cdb.exe", "certutil.exe", "cmd.exe", "cmstp.exe", "cscript.exe", "csi.exe", "dnx.exe", "dsget.exe",
125                  "dsquery.exe", "forfiles.exe", "fsi.exe", "ftp.exe", "gpresult.exe", "hostname.exe", "ieexec.exe",
126                  "iexpress.exe", "installutil.exe", "ipconfig.exe", "mshta.exe", "msxsl.exe", "nbtstat.exe", "net.exe",
127                  "net1.exe", "netsh.exe", "netstat.exe", "nltest.exe", "odbcconf.exe", "ping.exe", "powershell.exe",
128                  "pwsh.exe", "qprocess.exe", "quser.exe", "qwinsta.exe", "rcsi.exe", "reg.exe", "regasm.exe",
129                  "regsvcs.exe", "regsvr32.exe", "sc.exe", "schtasks.exe", "systeminfo.exe", "tasklist.exe",
130                  "tracert.exe", "whoami.exe", "wmic.exe", "wscript.exe", "xwizard.exe")
131'''
132
133
134[[rule.threat]]
135framework = "MITRE ATT&CK"
136
137[[rule.threat.technique]]
138id = "T1566"
139name = "Phishing"
140reference = "https://attack.mitre.org/techniques/T1566/"
141
142[[rule.threat.technique.subtechnique]]
143id = "T1566.001"
144name = "Spearphishing Attachment"
145reference = "https://attack.mitre.org/techniques/T1566/001/"
146
147[rule.threat.tactic]
148id = "TA0001"
149name = "Initial Access"
150reference = "https://attack.mitre.org/tactics/TA0001/"
151
152[[rule.threat]]
153framework = "MITRE ATT&CK"
154
155[[rule.threat.technique]]
156id = "T1059"
157name = "Command and Scripting Interpreter"
158reference = "https://attack.mitre.org/techniques/T1059/"
159
160[[rule.threat.technique.subtechnique]]
161id = "T1059.001"
162name = "PowerShell"
163reference = "https://attack.mitre.org/techniques/T1059/001/"
164
165[[rule.threat.technique.subtechnique]]
166id = "T1059.003"
167name = "Windows Command Shell"
168reference = "https://attack.mitre.org/techniques/T1059/003/"
169
170[[rule.threat.technique]]
171id = "T1204"
172name = "User Execution"
173reference = "https://attack.mitre.org/techniques/T1204/"
174
175[[rule.threat.technique.subtechnique]]
176id = "T1204.002"
177name = "Malicious File"
178reference = "https://attack.mitre.org/techniques/T1204/002/"
179
180[rule.threat.tactic]
181id = "TA0002"
182name = "Execution"
183reference = "https://attack.mitre.org/tactics/TA0002/"
184
185[[rule.threat]]
186framework = "MITRE ATT&CK"
187
188[[rule.threat.technique]]
189id = "T1218"
190name = "System Binary Proxy Execution"
191reference = "https://attack.mitre.org/techniques/T1218/"
192
193[[rule.threat.technique.subtechnique]]
194id = "T1218.003"
195name = "CMSTP"
196reference = "https://attack.mitre.org/techniques/T1218/003/"
197
198[[rule.threat.technique.subtechnique]]
199id = "T1218.004"
200name = "InstallUtil"
201reference = "https://attack.mitre.org/techniques/T1218/004/"
202
203[[rule.threat.technique.subtechnique]]
204id = "T1218.005"
205name = "Mshta"
206reference = "https://attack.mitre.org/techniques/T1218/005/"
207
208[[rule.threat.technique.subtechnique]]
209id = "T1218.008"
210name = "Odbcconf"
211reference = "https://attack.mitre.org/techniques/T1218/008/"
212
213[[rule.threat.technique.subtechnique]]
214id = "T1218.009"
215name = "Regsvcs/Regasm"
216reference = "https://attack.mitre.org/techniques/T1218/009/"
217
218[[rule.threat.technique.subtechnique]]
219id = "T1218.010"
220name = "Regsvr32"
221reference = "https://attack.mitre.org/techniques/T1218/010/"
222
223[rule.threat.tactic]
224id = "TA0005"
225name = "Defense Evasion"
226reference = "https://attack.mitre.org/tactics/TA0005/"