Suspicious CertUtil Commands

  1[metadata]
  2creation_date = "2020/02/18"
  3integration = ["endpoint", "windows", "system"]
  4maturity = "production"
  5updated_date = "2024/05/21"
  6
  7[transform]
  8[[transform.osquery]]
  9label = "Osquery - Retrieve DNS Cache"
 10query = "SELECT * FROM dns_cache"
 11
 12[[transform.osquery]]
 13label = "Osquery - Retrieve All Services"
 14query = "SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services"
 15
 16[[transform.osquery]]
 17label = "Osquery - Retrieve Services Running on User Accounts"
 18query = """
 19SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services WHERE
 20NOT (user_account LIKE '%LocalSystem' OR user_account LIKE '%LocalService' OR user_account LIKE '%NetworkService' OR
 21user_account == null)
 22"""
 23
 24[[transform.osquery]]
 25label = "Osquery - Retrieve Service Unsigned Executables with Virustotal Link"
 26query = """
 27SELECT concat('https://www.virustotal.com/gui/file/', sha1) AS VtLink, name, description, start_type, status, pid,
 28services.path FROM services JOIN authenticode ON services.path = authenticode.path OR services.module_path =
 29authenticode.path JOIN hash ON services.path = hash.path WHERE authenticode.result != 'trusted'
 30"""
 31
 32
 33[rule]
 34author = ["Elastic", "Austin Songer"]
 35description = """
 36Identifies suspicious commands being used with certutil.exe. CertUtil is a native Windows component which is part of
 37Certificate Services. CertUtil is often abused by attackers to live off the land for stealthier command and control or
 38data exfiltration.
 39"""
 40from = "now-9m"
 41index = [
 42    "winlogbeat-*",
 43    "logs-endpoint.events.process-*",
 44    "logs-windows.*",
 45    "endgame-*",
 46    "logs-system.security*",
 47]
 48language = "eql"
 49license = "Elastic License v2"
 50name = "Suspicious CertUtil Commands"
 51note = """## Triage and analysis
 52
 53### Investigating Suspicious CertUtil Commands
 54
 55`certutil.exe` is a command line utility program that is included with Microsoft Windows operating systems. It is used to manage and manipulate digital certificates and certificate services on computers running Windows.
 56
 57Attackers can abuse `certutil.exe` utility to download and/or deobfuscate malware, offensive security tools, and certificates from external sources to take the next steps in a compromised environment. This rule identifies command line arguments used to accomplish these behaviors.
 58
 59> **Note**:
 60> 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.
 61
 62#### Possible investigation steps
 63
 64- Investigate the script 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.
 65- Investigate other alerts associated with the user/host during the past 48 hours.
 66- Examine the command line to determine the nature of the execution.
 67  - If files were downloaded, retrieve them and check whether they were run, and under which security context.
 68  - If files were obfuscated or deobfuscated, retrieve them.
 69- Examine the host for derived artifacts that indicate suspicious activities:
 70  - Analyze the involved files using a private sandboxed analysis system.
 71  - Observe and collect information about the following activities in both the sandbox and the alert subject host:
 72    - Attempts to contact external domains and addresses.
 73      - Use the Elastic Defend network events to determine domains and addresses contacted by the subject process by filtering by the process' `process.entity_id`.
 74      - Examine the DNS cache for suspicious or anomalous entries.
 75        - $osquery_0
 76    - Use the Elastic Defend registry events to examine registry keys accessed, modified, or created by the related processes in the process tree.
 77    - Examine the host services for suspicious or anomalous entries.
 78      - $osquery_1
 79      - $osquery_2
 80      - $osquery_3
 81  - 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.
 82
 83### False positive analysis
 84
 85- If this rule is noisy in your environment due to expected activity, consider adding exceptions — preferably with a combination of user and command line conditions.
 86
 87### Response and remediation
 88
 89- Initiate the incident response process based on the outcome of the triage.
 90- Isolate the involved host to prevent further post-compromise behavior.
 91- If the triage identified malware, search the environment for additional compromised hosts.
 92  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 93  - Stop suspicious processes.
 94  - Immediately block the identified indicators of compromise (IoCs).
 95  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 96- Remove and block malicious artifacts identified during triage.
 97- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
 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"""
101references = [
102    "https://twitter.com/Moriarty_Meng/status/984380793383370752",
103    "https://twitter.com/egre55/status/1087685529016193025",
104    "https://www.sysadmins.lv/blog-en/certutil-tips-and-tricks-working-with-x509-file-format.aspx",
105    "https://docs.microsoft.com/en-us/archive/blogs/pki/basic-crl-checking-with-certutil",
106]
107risk_score = 47
108rule_id = "fd70c98a-c410-42dc-a2e3-761c71848acf"
109severity = "medium"
110tags = [
111    "Domain: Endpoint",
112    "OS: Windows",
113    "Use Case: Threat Detection",
114    "Tactic: Defense Evasion",
115    "Data Source: Elastic Endgame",
116    "Resources: Investigation Guide",
117    "Data Source: Elastic Defend",
118]
119timeline_id = "e70679c2-6cde-4510-9764-4823df18f7db"
120timeline_title = "Comprehensive Process Timeline"
121timestamp_override = "event.ingested"
122type = "eql"
123
124query = '''
125process where host.os.type == "windows" and event.type == "start" and
126  (process.name : "certutil.exe" or ?process.pe.original_file_name == "CertUtil.exe") and
127  process.args : ("?decode", "?encode", "?urlcache", "?verifyctl", "?encodehex", "?decodehex", "?exportPFX")
128'''
129
130
131[[rule.threat]]
132framework = "MITRE ATT&CK"
133[[rule.threat.technique]]
134id = "T1140"
135name = "Deobfuscate/Decode Files or Information"
136reference = "https://attack.mitre.org/techniques/T1140/"
137
138
139[rule.threat.tactic]
140id = "TA0005"
141name = "Defense Evasion"
142reference = "https://attack.mitre.org/tactics/TA0005/"