Suspicious Process from Conhost

  1[metadata]
  2creation_date = "2020/08/31"
  3deprecation_date = "2022/08/03"
  4maturity = "deprecated"
  5updated_date = "2022/08/03"
  6
  7[rule]
  8author = ["Elastic"]
  9description = "Identifies a suspicious Conhost child process which may be an indication of code injection activity."
 10from = "now-9m"
 11index = ["winlogbeat-*", "logs-endpoint.events.*", "logs-windows.*"]
 12language = "eql"
 13license = "Elastic License v2"
 14name = "Suspicious Process from Conhost"
 15note = """## Triage and analysis
 16
 17### Investigating Suspicious Process from Conhost
 18
 19The Windows Console Host, or `conhost.exe`, is both the server application for all of the Windows Console APIs as well as
 20the classic Windows user interface for working with command-line applications.
 21
 22The `conhost.exe` process doesn't normally have child processes. Any processes spawned by the `conhost.exe` process can indicate code
 23injection activity or a suspicious process masquerading as the `conhost.exe` process.
 24
 25#### Possible investigation steps
 26
 27- Investigate the process execution chain (parent process tree) for unknown processes. Examine their executable files
 28for prevalence, whether they are located in expected locations, and if they are signed with valid digital signatures.
 29- Investigate abnormal behaviors observed by the subject process, such as network connections, registry or file
 30modifications, and any spawned child processes.
 31- Investigate other alerts associated with the user/host during the past 48 hours.
 32- Inspect the host for suspicious or abnormal behaviors in the alert timeframe.
 33- Retrieve the process executable and determine if it is 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 tasks 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### Related rules
 44
 45- Conhost Spawned By Suspicious Parent Process - 05b358de-aa6d-4f6c-89e6-78f74018b43b
 46- Suspicious PowerShell Engine ImageLoad - 852c1f19-68e8-43a6-9dce-340771fe1be3
 47
 48### False positive analysis
 49
 50- This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.
 51
 52### Response and remediation
 53
 54- Initiate the incident response process based on the outcome of the triage.
 55- Isolate the involved hosts to prevent further post-compromise behavior.
 56- If the triage identified malware, search the environment for additional compromised hosts.
 57  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 58  - Stop suspicious processes.
 59  - Immediately block the identified indicators of compromise (IoCs).
 60  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that
 61  attackers could use to reinfect the system.
 62- Remove and block malicious artifacts identified during triage.
 63- Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are
 64identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business
 65systems, and web services.
 66- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and
 67malware components.
 68- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 69- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the
 70mean time to respond (MTTR).
 71
 72## Setup
 73
 74If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define `event.ingested` and default fallback for EQL rules was not added until 8.2, so you will need to add a custom pipeline to populate `event.ingested` to @timestamp for this rule to work.
 75"""
 76references = [
 77    "https://modexp.wordpress.com/2018/09/12/process-injection-user-data/",
 78    "https://github.com/sbousseaden/EVTX-ATTACK-SAMPLES/blob/master/Defense%20Evasion/evasion_codeinj_odzhan_conhost_sysmon_10_1.evtx",
 79]
 80risk_score = 73
 81rule_id = "28896382-7d4f-4d50-9b72-67091901fd26"
 82severity = "high"
 83tags = ["Elastic", "Host", "Windows", "Threat Detection", "Defense Evasion"]
 84timestamp_override = "event.ingested"
 85type = "eql"
 86
 87query = '''
 88process where event.type in ("start", "process_started") and
 89  process.parent.name : "conhost.exe" and
 90  not process.executable : ("?:\\Windows\\splwow64.exe", "?:\\Windows\\System32\\WerFault.exe", "?:\\Windows\\System32\\conhost.exe")
 91'''
 92
 93
 94[[rule.threat]]
 95framework = "MITRE ATT&CK"
 96[[rule.threat.technique]]
 97id = "T1055"
 98name = "Process Injection"
 99reference = "https://attack.mitre.org/techniques/T1055/"
100
101
102[rule.threat.tactic]
103id = "TA0005"
104name = "Defense Evasion"
105reference = "https://attack.mitre.org/tactics/TA0005/"