Long Base64 Encoded Command via Scripting Interpreter

[metadata]
creation_date = "2026/03/27"
integration = ["endpoint"]
maturity = "production"
updated_date = "2026/10/06"

[rule]
author = ["Elastic"]
description = """
Identifies oversized command lines used by Python, PowerShell, Node.js, or Deno that contain base64 decoding or
encoded-command patterns. Adversaries may embed long inline encoded payloads in scripting interpreters to evade
inspection and execute malicious content across Windows, macOS, and Linux systems.
"""
from = "now-9m"
language = "esql"
license = "Elastic License v2"
name = "Long Base64 Encoded Command via Scripting Interpreter"
note = """## Triage and analysis

### Investigating Long Base64 Encoded Command via Scripting Interpreter

This rule detects process start events where the original `process.command_line` field was ignored at index time due to
its size, but the full command line remains available in `process.command_line.text`. Attackers commonly use very long
base64-encoded inline commands with interpreters such as Python, PowerShell, Node.js, and Deno to conceal payloads and
avoid straightforward command-line inspection.

### Possible investigation steps

- Review `process.command_line.text` to determine whether the encoded content includes shell commands, scripts, URLs, or embedded payloads.
- Inspect the parent process and execution chain to understand how the interpreter was launched and whether it originated from a browser, office application, archive utility, or remote access tool.
- Check whether the same host or user generated additional suspicious process, network, or file events around the same time.
- If the payload can be safely decoded in an isolated environment, inspect the decoded content for follow-on execution, credential access, persistence, or download behavior.

### False positive analysis

- Administrative automation, packaging workflows, or developer tooling may legitimately pass large encoded blobs to scripting interpreters.
- PowerShell remoting, software deployment frameworks, or internal bootstrap scripts can occasionally use encoded commands; validate the source, user, and expected automation context.

### Response and remediation

- Isolate the affected host if the decoded content or surrounding activity indicates malicious execution.
- Terminate the suspicious interpreter process and any spawned child processes.
- Preserve the full command line and related process tree for forensic analysis before making changes on the host.
- Reset or revoke any credentials, tokens, or secrets exposed by the decoded payload or subsequent attacker activity.
"""
risk_score = 73
rule_id = "74d31cb7-4a2c-44fe-9d1d-f375b9f3cb61"
severity = "high"
tags = [
    "Domain: Endpoint",
    "OS: Windows",
    "OS: macOS",
    "OS: Linux",
    "Use Case: Threat Detection",
    "Tactic: Defense Evasion",
    "Tactic: Execution",
    "Data Source: Elastic Defend",
    "Resources: Investigation Guide",
    "Noise: Unknown",
    "Performance: Normal",
    "Profile: Recommended",
    "Threat: Encoding-Based Obfuscation",
    "Threat: Script-Based Execution",
    "Rule Type: ES|QL",
    "Platform: Windows",
    "Platform: Linux",
    "Platform: macOS",
]
timestamp_override = "event.ingested"
type = "esql"

query = '''
FROM logs-endpoint.events.process-* METADATA _id, _index, _version, _ignored
| MV_EXPAND _ignored
| WHERE _ignored == "process.command_line"
| WHERE event.category == "process" and event.type == "start"
| EVAL command_line = TO_LOWER(process.command_line.text),
       pname = TO_LOWER(process.name)
| EVAL has_long_base64 = command_line RLIKE """.*[a-z0-9+/]{100,}={0,2}.*"""
| WHERE
(
    (
        /* Python: decode primitive + plausible Base64 payload */
        pname LIKE "python*" AND
        has_long_base64 AND
        (
            command_line LIKE "*b64decode*" OR
            (command_line LIKE "*-c*" AND command_line LIKE "*base64*")
        ) AND NOT (process.parent.name == "codex" AND (command_line LIKE "*.write(base64.*" or command_line LIKE "*.write_bytes(base64*"))
    ) OR
    (
        /* PowerShell: encoded command or explicit Base64 decode + payload */
        (pname LIKE "powershell*" OR pname LIKE "pwsh*") AND
        has_long_base64 AND
        (
            command_line RLIKE """.* -(e|en|enc|enco|encod|encode|encoded|encodedcommand) .+""" OR
            command_line LIKE "*-encodedcommand*" OR
            command_line LIKE "*frombase64string*"
        )
    ) OR
    (
        /* Node.js */
        pname LIKE "node*" AND
        has_long_base64 AND
        (
            (command_line LIKE "*buffer.from*" AND command_line LIKE "*base64*") OR
            command_line LIKE "*atob(*"
        )
    ) OR
    (
        /* Deno */
        pname LIKE "deno*" AND
        has_long_base64 AND
        (
            command_line LIKE "*atob(*" OR
            (command_line LIKE "*buffer.from*" AND command_line LIKE "*base64*") OR
            command_line LIKE "*eval(*"
        )
    )
)
| EVAL Esql.length_cmdline = LENGTH(command_line)
| WHERE Esql.length_cmdline >= 4000
| DROP _ignored, pname, has_long_base64
| KEEP @timestamp, _id, _version, _index, data_stream.namespace,
       user.name, user.id, host.name, host.id, agent.id,
       process.entity_id, process.executable,
       process.parent.entity_id, process.parent.executable,
       process.command_line.text, process.parent.command_line
'''

[rule.alert_suppression]
group_by = ["host.id", "process.executable", "process.parent.executable"]
duration = {value = 8, unit = "h"}
missing_fields_strategy = "suppress"

[[rule.threat]]
framework = "MITRE ATT&CK"

[[rule.threat.technique]]
id = "T1027"
name = "Obfuscated Files or Information"
reference = "https://attack.mitre.org/techniques/T1027/"

[[rule.threat.technique]]
id = "T1140"
name = "Deobfuscate/Decode Files or Information"
reference = "https://attack.mitre.org/techniques/T1140/"

[rule.threat.tactic]
id = "TA0005"
name = "Defense Evasion"
reference = "https://attack.mitre.org/tactics/TA0005/"

[[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.technique.subtechnique]]
id = "T1059.001"
name = "PowerShell"
reference = "https://attack.mitre.org/techniques/T1059/001/"

[[rule.threat.technique.subtechnique]]
id = "T1059.006"
name = "Python"
reference = "https://attack.mitre.org/techniques/T1059/006/"

[[rule.threat.technique.subtechnique]]
id = "T1059.007"
name = "JavaScript"
reference = "https://attack.mitre.org/techniques/T1059/007/"

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