Remote File Download via Script Interpreter

  1[metadata]
  2creation_date = "2020/11/29"
  3integration = ["endpoint", "windows"]
  4maturity = "production"
  5updated_date = "2024/10/15"
  6min_stack_version = "8.14.0"
  7min_stack_comments = "Breaking change at 8.14.0 for the Windows Integration."
  8
  9[transform]
 10[[transform.osquery]]
 11label = "Osquery - Retrieve DNS Cache"
 12query = "SELECT * FROM dns_cache"
 13
 14[[transform.osquery]]
 15label = "Osquery - Retrieve All Services"
 16query = "SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services"
 17
 18[[transform.osquery]]
 19label = "Osquery - Retrieve Services Running on User Accounts"
 20query = """
 21SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services WHERE
 22NOT (user_account LIKE '%LocalSystem' OR user_account LIKE '%LocalService' OR user_account LIKE '%NetworkService' OR
 23user_account == null)
 24"""
 25
 26[[transform.osquery]]
 27label = "Osquery - Retrieve Service Unsigned Executables with Virustotal Link"
 28query = """
 29SELECT concat('https://www.virustotal.com/gui/file/', sha1) AS VtLink, name, description, start_type, status, pid,
 30services.path FROM services JOIN authenticode ON services.path = authenticode.path OR services.module_path =
 31authenticode.path JOIN hash ON services.path = hash.path WHERE authenticode.result != 'trusted'
 32"""
 33
 34
 35[rule]
 36author = ["Elastic"]
 37description = """
 38Identifies built-in Windows script interpreters (cscript.exe or wscript.exe) being used to download an executable file
 39from a remote destination.
 40"""
 41from = "now-9m"
 42index = [
 43    "winlogbeat-*",
 44    "logs-endpoint.events.network-*",
 45    "logs-endpoint.events.file-*",
 46    "logs-windows.sysmon_operational-*",
 47]
 48language = "eql"
 49license = "Elastic License v2"
 50name = "Remote File Download via Script Interpreter"
 51note = """## Triage and analysis
 52
 53### Investigating Remote File Download via Script Interpreter
 54
 55The Windows Script Host (WSH) is a Windows automation technology, which is ideal for non-interactive scripting needs, such as logon scripting, administrative scripting, and machine automation.
 56
 57Attackers commonly use WSH scripts as their initial access method, acting like droppers for second stage payloads, but can also use them to download tools and utilities needed to accomplish their goals.
 58
 59This rule looks for DLLs and executables downloaded using `cscript.exe` or `wscript.exe`.
 60
 61> **Note**:
 62> This investigation guide uses the [Osquery Markdown Plugin](https://www.elastic.co/guide/en/security/master/invest-guide-run-osquery.html) introduced in Elastic Stack version 8.5.0. Older Elastic Stack versions will display unrendered Markdown in this guide.
 63
 64#### Possible investigation steps
 65
 66- 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.
 67- Examine the host for derived artifacts that indicate suspicious activities:
 68  - Analyze both the script and the executable involved using a private sandboxed analysis system.
 69  - Observe and collect information about the following activities in both the sandbox and the alert subject host:
 70    - Attempts to contact external domains and addresses.
 71      - Use the Elastic Defend network events to determine domains and addresses contacted by the subject process by filtering by the process' `process.entity_id`.
 72      - Examine the DNS cache for suspicious or anomalous entries.
 73        - $osquery_0
 74    - Use the Elastic Defend registry events to examine registry keys accessed, modified, or created by the related processes in the process tree.
 75    - Examine the host services for suspicious or anomalous entries.
 76      - $osquery_1
 77      - $osquery_2
 78      - $osquery_3
 79  - Retrieve the files' SHA-256 hash values using the PowerShell `Get-FileHash` cmdlet and search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
 80- Investigate potentially compromised accounts. Analysts can do this by searching for login events (for example, 4624) to the target host after the registry modification.
 81
 82### False positive analysis
 83
 84- The usage of these script engines by regular users is unlikely. In the case of authorized benign true positives (B-TPs), exceptions can be added.
 85
 86### Response and remediation
 87
 88- Initiate the incident response process based on the outcome of the triage.
 89- Isolate the involved host to prevent further post-compromise behavior.
 90- If the triage identified malware, search the environment for additional compromised hosts.
 91  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 92  - Stop suspicious processes.
 93  - Immediately block the identified indicators of compromise (IoCs).
 94  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 95- Remove and block malicious artifacts identified during triage.
 96- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
 97- 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.
 98- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 99- 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).
100"""
101risk_score = 47
102rule_id = "1d276579-3380-4095-ad38-e596a01bc64f"
103severity = "medium"
104tags = [
105    "Domain: Endpoint",
106    "OS: Windows",
107    "Use Case: Threat Detection",
108    "Tactic: Command and Control",
109    "Tactic: Execution",
110    "Resources: Investigation Guide",
111    "Data Source: Elastic Defend",
112    "Data Source: Sysmon",
113]
114type = "eql"
115
116query = '''
117sequence by host.id, process.entity_id
118  [network where host.os.type == "windows" and process.name : ("wscript.exe", "cscript.exe") and network.protocol != "dns" and
119   network.direction : ("outgoing", "egress") and network.type == "ipv4" and destination.ip != "127.0.0.1"
120  ]
121  [file where host.os.type == "windows" and event.type == "creation" and file.extension : ("exe", "dll")]
122'''
123
124
125[[rule.threat]]
126framework = "MITRE ATT&CK"
127[[rule.threat.technique]]
128id = "T1105"
129name = "Ingress Tool Transfer"
130reference = "https://attack.mitre.org/techniques/T1105/"
131
132
133[rule.threat.tactic]
134id = "TA0011"
135name = "Command and Control"
136reference = "https://attack.mitre.org/tactics/TA0011/"
137[[rule.threat]]
138framework = "MITRE ATT&CK"
139[[rule.threat.technique]]
140id = "T1059"
141name = "Command and Scripting Interpreter"
142reference = "https://attack.mitre.org/techniques/T1059/"
143[[rule.threat.technique.subtechnique]]
144id = "T1059.005"
145name = "Visual Basic"
146reference = "https://attack.mitre.org/techniques/T1059/005/"
147
148
149
150[rule.threat.tactic]
151id = "TA0002"
152name = "Execution"
153reference = "https://attack.mitre.org/tactics/TA0002/"