Command Line Obfuscation via Whitespace Padding

  1[metadata]
  2creation_date = "2025/06/30"
  3integration = ["endpoint", "system", "windows", "auditd_manager", "m365_defender", "crowdstrike", "sentinel_one_cloud_funnel"]
  4maturity = "production"
  5updated_date = "2025/06/30"
  6
  7[rule]
  8author = ["Elastic"]
  9description = """
 10Identifies process execution events where the command line value contains a long sequence of whitespace characters or
 11multiple occurrences of contiguous whitespace. Attackers may attempt to evade signature-based detections by padding
 12their malicious command with unnecessary whitespace characters. These observations should be investigated for malicious
 13behavior.
 14"""
 15from = "now-9m"
 16language = "esql"
 17license = "Elastic License v2"
 18name = "Command Line Obfuscation via Whitespace Padding"
 19note = """## Triage and analysis
 20
 21### Investigating Command Line Obfuscation via Whitespace Padding
 22
 23This rule identifies process execution events where the command line value contains a long sequence of whitespace
 24characters or multiple occurrences of contiguous whitespace. Attackers may attempt to evade signature-based detections
 25by padding their malicious command with unnecessary whitespace characters.
 26
 27#### Possible investigation steps
 28
 29- Analyze the command line of the process in question for evidence of malicious code execution.
 30- Investigate the process execution chain (parent process tree) for unknown processes. Examine their executable files
 31for prevalence, whether they are located in expected locations, and if they are signed with valid digital signatures.
 32- Investigate other alerts associated with the user/host during the past 48 hours.
 33- Investigate abnormal behaviors observed by the subject process such as network connections, registry or file
 34modifications, and any spawned child processes.
 35- Retrieve the process executable and determine if it is malicious:
 36  - Use a private sandboxed malware analysis system to perform analysis.
 37    - Observe and collect information about the following activities:
 38      - Attempts to contact external domains and addresses.
 39      - File and registry access, modification, and creation activities.
 40      - Service creation and launch activities.
 41      - Scheduled tasks creation.
 42  - Use the PowerShell `Get-FileHash` cmdlet to get the files' SHA-256 hash values.
 43    - Search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
 44
 45### False positive analysis
 46
 47- Alerts derived from this rule are not inherently malicious. Analysts can dismiss the alert if they don't find enough
 48evidence of further suspicious activity.
 49
 50### Response and remediation
 51
 52- Initiate the incident response process based on the outcome of the triage.
 53- Isolate the involved host to prevent further post-compromise behavior.
 54- If the triage identified malware, search the environment for additional compromised hosts.
 55  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 56  - Stop suspicious processes.
 57  - Immediately block the identified indicators of compromise (IoCs).
 58  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that
 59  attackers could use to reinfect the system.
 60- Remove the malicious certificate from the root certificate store.
 61- Remove and block malicious artifacts identified during triage.
 62- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and
 63malware components.
 64- Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are
 65identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business
 66systems, and web services.
 67- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 68- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the
 69mean time to respond (MTTR).
 70"""
 71risk_score = 47
 72rule_id = "5a876e0d-d39a-49b9-8ad8-19c9b622203b"
 73severity = "medium"
 74tags = [
 75    "Domain: Endpoint",
 76    "OS: Windows",
 77    "OS: macOS",
 78    "OS: Linux",
 79    "Use Case: Threat Detection",
 80    "Tactic: Defense Evasion",
 81    "Tactic: Execution",
 82    "Resources: Investigation Guide"
 83]
 84timestamp_override = "event.ingested"
 85type = "esql"
 86
 87query = '''
 88FROM logs-* metadata _id, _version, _index 
 89| where event.category == "process" and event.type == "start" and event.action != "fork"
 90// more than 100 spaces in process.command_line
 91| eval multi_spaces = LOCATE(process.command_line, space(100)) 
 92| where multi_spaces > 0 
 93| keep user.name, host.id, host.name, process.command_line, process.executable, process.parent.executable
 94'''
 95
 96
 97[[rule.threat]]
 98framework = "MITRE ATT&CK"
 99[[rule.threat.technique]]
100id = "T1027"
101name = "Obfuscated Files or Information"
102reference = "https://attack.mitre.org/techniques/T1027/"
103
104[[rule.threat.technique]]
105id = "T1140"
106name = "Deobfuscate/Decode Files or Information"
107reference = "https://attack.mitre.org/techniques/T1140/"
108
109
110[rule.threat.tactic]
111id = "TA0005"
112name = "Defense Evasion"
113reference = "https://attack.mitre.org/tactics/TA0005/"
114[[rule.threat]]
115framework = "MITRE ATT&CK"
116[[rule.threat.technique]]
117id = "T1059"
118name = "Command and Scripting Interpreter"
119reference = "https://attack.mitre.org/techniques/T1059/"
120[[rule.threat.technique.subtechnique]]
121id = "T1059.001"
122name = "PowerShell"
123reference = "https://attack.mitre.org/techniques/T1059/001/"
124
125
126
127[rule.threat.tactic]
128id = "TA0002"
129name = "Execution"
130reference = "https://attack.mitre.org/tactics/TA0002/"