Whitespace Padding in Process Command Line

  1[metadata]
  2creation_date = "2021/07/30"
  3deprecation_date = "2022/08/02"
  4maturity = "deprecated"
  5min_stack_comments = "EQL regex had a bug when dealing with wildcard fields that was fixed in 7.16 (elastic/elasticsearch/issues/78391)"
  6min_stack_version = "7.16.0"
  7updated_date = "2022/08/02"
  8
  9[rule]
 10author = ["Elastic"]
 11description = """
 12Identifies process execution events where the command line value contains a long sequence of whitespace characters or
 13multiple occurrences of contiguous whitespace. Attackers may attempt to evade signature-based detections by padding
 14their malicious command with unnecessary whitespace characters. These observations should be investigated for malicious
 15behavior.
 16"""
 17from = "now-9m"
 18index = ["winlogbeat-*", "logs-endpoint.events.*", "logs-windows.*"]
 19language = "eql"
 20license = "Elastic License v2"
 21name = "Whitespace Padding in Process Command Line"
 22note = """## Triage and analysis
 23
 24### Investigating Whitespace Padding in Process Command Line
 25
 26This rule identifies process execution events where the command line value contains a long sequence of whitespace
 27characters or multiple occurrences of contiguous whitespace. Attackers may attempt to evade signature-based detections
 28by padding their malicious command with unnecessary whitespace characters.
 29
 30#### Possible investigation steps
 31
 32- Analyze the command line of the process in question for evidence of malicious code execution.
 33- Investigate the process execution chain (parent process tree) for unknown processes. Examine their executable files
 34for prevalence, whether they are located in expected locations, and if they are signed with valid digital signatures.
 35- Investigate other alerts associated with the user/host during the past 48 hours.
 36- Investigate abnormal behaviors observed by the subject process such as network connections, registry or file
 37modifications, and any spawned child processes.
 38- Retrieve the process executable and determine if it is malicious:
 39  - Use a private sandboxed malware analysis system to perform analysis.
 40    - Observe and collect information about the following activities:
 41      - Attempts to contact external domains and addresses.
 42      - File and registry access, modification, and creation activities.
 43      - Service creation and launch activities.
 44      - Scheduled tasks creation.
 45  - Use the PowerShell `Get-FileHash` cmdlet to get the files' SHA-256 hash values.
 46    - Search for the existence and reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.
 47
 48### False positive analysis
 49
 50- Alerts derived from this rule are not inherently malicious. Analysts can dismiss the alert if they don't find enough
 51evidence of further suspicious activity.
 52
 53### Response and remediation
 54
 55- Initiate the incident response process based on the outcome of the triage.
 56- Isolate the involved host to prevent further post-compromise behavior.
 57- If the triage identified malware, search the environment for additional compromised hosts.
 58  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 59  - Stop suspicious processes.
 60  - Immediately block the identified indicators of compromise (IoCs).
 61  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that
 62  attackers could use to reinfect the system.
 63- Remove the malicious certificate from the root certificate store.
 64- Remove and block malicious artifacts identified during triage.
 65- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and
 66malware components.
 67- Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are
 68identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business
 69systems, and web services.
 70- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 71- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the
 72mean time to respond (MTTR).
 73
 74## Setup
 75
 76If 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.
 77"""
 78references = ["https://twitter.com/JohnLaTwC/status/1419251082736201737"]
 79risk_score = 47
 80rule_id = "e0dacebe-4311-4d50-9387-b17e89c2e7fd"
 81severity = "medium"
 82tags = ["Elastic", "Host", "Windows", "Threat Detection", "Defense Evasion"]
 83timestamp_override = "event.ingested"
 84type = "eql"
 85
 86query = '''
 87process where event.type in ("start", "process_started") and
 88  process.command_line regex ".*[ ]{20,}.*" or
 89
 90  /* this will match on 3 or more separate occurrences of 3+ contiguous whitespace characters */
 91  process.command_line regex "([^ ]+[ ]{3,}[^ ]*){3,}.*"
 92'''
 93
 94
 95[[rule.threat]]
 96framework = "MITRE ATT&CK"
 97
 98[rule.threat.tactic]
 99id = "TA0005"
100name = "Defense Evasion"
101reference = "https://attack.mitre.org/tactics/TA0005/"