sigma-rules/rules/windows/execution_via_hidden_shell_conhost.toml

[metadata]
creation_date = "2020/08/17"
integration = ["endpoint", "windows"]
maturity = "production"
min_stack_comments = "New fields added: required_fields, related_integrations, setup"
min_stack_version = "8.3.0"
updated_date = "2023/02/22"

[rule]
author = ["Elastic"]
description = """
Detects when the Console Window Host (conhost.exe) process is spawned by a suspicious parent process, which could be
indicative of code injection.
"""
from = "now-9m"
index = ["winlogbeat-*", "logs-endpoint.events.*", "logs-windows.*", "endgame-*"]
language = "eql"
license = "Elastic License v2"
name = "Conhost Spawned By Suspicious Parent Process"
note = """## Triage and analysis

### Investigating Conhost Spawned By Suspicious Parent Process

The 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.

Attackers 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.

#### 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 abnormal behaviors observed by the subject process, such as network connections, registry or file modifications, and any spawned child processes.
- Investigate other alerts associated with the user/host during the past 48 hours.
- Inspect the host for suspicious or abnormal behavior in the alert timeframe.
- Retrieve the parent process executable and determine if it is 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.

### Related rules

- Suspicious Process from Conhost - 28896382-7d4f-4d50-9b72-67091901fd26
- Suspicious PowerShell Engine ImageLoad - 852c1f19-68e8-43a6-9dce-340771fe1be3

### Response and remediation

- Initiate the incident response process based on the outcome of the triage.
- Isolate the involved hosts to prevent further post-compromise behavior.
- 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.
- 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.
- 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.
- 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).

## Setup

If 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.
"""
references = [
    "https://www.fireeye.com/blog/threat-research/2017/08/monitoring-windows-console-activity-part-one.html",
]
risk_score = 73
rule_id = "05b358de-aa6d-4f6c-89e6-78f74018b43b"
severity = "high"
tags = ["Elastic", "Host", "Windows", "Threat Detection", "Execution", "Investigation Guide", "Elastic Endgame"]
timestamp_override = "event.ingested"
type = "eql"

query = '''
process where host.os.type == "windows" and event.type == "start" and
  process.name : "conhost.exe" and
  process.parent.name : ("lsass.exe", "services.exe", "smss.exe", "winlogon.exe", "explorer.exe", "dllhost.exe", "rundll32.exe",
                         "regsvr32.exe", "userinit.exe", "wininit.exe", "spoolsv.exe", "ctfmon.exe") and
  not (process.parent.name : "rundll32.exe" and
       process.parent.args : ("?:\\Windows\\Installer\\MSI*.tmp,zzzzInvokeManagedCustomActionOutOfProc",
                              "?:\\WINDOWS\\system32\\PcaSvc.dll,PcaPatchSdbTask",
                              "?:\\WINDOWS\\system32\\davclnt.dll,DavSetCookie"))
'''


[[rule.threat]]
framework = "MITRE ATT&CK"
[[rule.threat.technique]]
id = "T1059"
name = "Command and Scripting Interpreter"
reference = "https://attack.mitre.org/techniques/T1059/"


[rule.threat.tactic]
id = "TA0002"
name = "Execution"
reference = "https://attack.mitre.org/tactics/TA0002/"