Conhost Spawned By Suspicious Parent Process

  1[metadata]
  2creation_date = "2020/08/17"
  3integration = ["endpoint", "windows", "m365_defender", "sentinel_one_cloud_funnel"]
  4maturity = "production"
  5updated_date = "2025/03/20"
  6
  7[rule]
  8author = ["Elastic"]
  9description = """
 10Detects when the Console Window Host (conhost.exe) process is spawned by a suspicious parent process, which could be
 11indicative of code injection.
 12"""
 13from = "now-9m"
 14index = [
 15    "winlogbeat-*",
 16    "logs-endpoint.events.process-*",
 17    "logs-windows.sysmon_operational-*",
 18    "endgame-*",
 19    "logs-m365_defender.event-*",
 20    "logs-sentinel_one_cloud_funnel.*",
 21]
 22language = "eql"
 23license = "Elastic License v2"
 24name = "Conhost Spawned By Suspicious Parent Process"
 25note = """## Triage and analysis
 26
 27### Investigating Conhost Spawned By Suspicious Parent Process
 28
 29The Windows Console Host, or `conhost.exe`, is both the server application for all of the Windows Console APIs as well as the classic Windows user interface for working with command-line applications.
 30
 31Attackers often rely on custom shell implementations to avoid using built-in command interpreters like `cmd.exe` and `PowerShell.exe` and bypass application allowlisting and security features. Attackers commonly inject these implementations into legitimate system processes.
 32
 33#### Possible investigation steps
 34
 35- 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.
 36- Investigate abnormal behaviors observed by the subject process, such as network connections, registry or file modifications, and any spawned child processes.
 37- Investigate other alerts associated with the user/host during the past 48 hours.
 38- Inspect the host for suspicious or abnormal behavior in the alert timeframe.
 39- Retrieve the parent process executable and determine if it is malicious:
 40  - Use a private sandboxed malware analysis system to perform analysis.
 41    - Observe and collect information about the following activities:
 42      - Attempts to contact external domains and addresses.
 43      - File and registry access, modification, and creation activities.
 44      - Service creation and launch activities.
 45      - Scheduled task creation.
 46  - Use the PowerShell `Get-FileHash` cmdlet to get the files' SHA-256 hash values.
 47    - Search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
 48
 49### False positive analysis
 50
 51- This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.
 52
 53### Related rules
 54
 55- Suspicious Process from Conhost - 28896382-7d4f-4d50-9b72-67091901fd26
 56- Suspicious PowerShell Engine ImageLoad - 852c1f19-68e8-43a6-9dce-340771fe1be3
 57
 58### Response and remediation
 59
 60- Initiate the incident response process based on the outcome of the triage.
 61- Isolate the involved hosts to prevent further post-compromise behavior.
 62- If the triage identified malware, search the environment for additional compromised hosts.
 63  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 64  - Stop suspicious processes.
 65  - Immediately block the identified indicators of compromise (IoCs).
 66  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 67- Remove and block malicious artifacts identified during triage.
 68- 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.
 69- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
 70- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 71- 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).
 72"""
 73references = [
 74    "https://www.fireeye.com/blog/threat-research/2017/08/monitoring-windows-console-activity-part-one.html",
 75]
 76risk_score = 73
 77rule_id = "05b358de-aa6d-4f6c-89e6-78f74018b43b"
 78severity = "high"
 79tags = [
 80    "Domain: Endpoint",
 81    "OS: Windows",
 82    "Use Case: Threat Detection",
 83    "Tactic: Execution",
 84    "Tactic: Defense Evasion",
 85    "Tactic: Privilege Escalation",
 86    "Resources: Investigation Guide",
 87    "Data Source: Elastic Endgame",
 88    "Data Source: Elastic Defend",
 89    "Data Source: Sysmon",
 90    "Data Source: Microsoft Defender for Endpoint",
 91    "Data Source: SentinelOne",
 92]
 93timestamp_override = "event.ingested"
 94type = "eql"
 95
 96query = '''
 97process where host.os.type == "windows" and event.type == "start" and
 98  process.name : "conhost.exe" and
 99  process.parent.name : ("lsass.exe", "services.exe", "smss.exe", "winlogon.exe", "explorer.exe", "dllhost.exe", "rundll32.exe",
100                         "regsvr32.exe", "userinit.exe", "wininit.exe", "spoolsv.exe", "ctfmon.exe") and
101  not (process.parent.name : "rundll32.exe" and
102       process.parent.args : ("?:\\Windows\\Installer\\MSI*.tmp,zzzzInvokeManagedCustomActionOutOfProc",
103                              "?:\\WINDOWS\\system32\\PcaSvc.dll,PcaPatchSdbTask",
104                              "?:\\WINDOWS\\system32\\davclnt.dll,DavSetCookie"))
105'''
106
107
108[[rule.threat]]
109framework = "MITRE ATT&CK"
110[[rule.threat.technique]]
111id = "T1059"
112name = "Command and Scripting Interpreter"
113reference = "https://attack.mitre.org/techniques/T1059/"
114
115
116[rule.threat.tactic]
117id = "TA0002"
118name = "Execution"
119reference = "https://attack.mitre.org/tactics/TA0002/"
120[[rule.threat]]
121framework = "MITRE ATT&CK"
122[[rule.threat.technique]]
123id = "T1036"
124name = "Masquerading"
125reference = "https://attack.mitre.org/techniques/T1036/"
126
127
128[rule.threat.tactic]
129id = "TA0005"
130name = "Defense Evasion"
131reference = "https://attack.mitre.org/tactics/TA0005/"
132[[rule.threat]]
133framework = "MITRE ATT&CK"
134[[rule.threat.technique]]
135id = "T1055"
136name = "Process Injection"
137reference = "https://attack.mitre.org/techniques/T1055/"
138
139
140[rule.threat.tactic]
141id = "TA0004"
142name = "Privilege Escalation"
143reference = "https://attack.mitre.org/tactics/TA0004/"