Long Base64 Encoded Command via Scripting Interpreter

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

[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",
]
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)
| WHERE 
(
    (
        /* Python: inline exec with base64 decode or -c flag with encoded payload */
        pname like "python*" and
        (
            command_line like "*b64decode*" or
            (command_line like "*-c*" and command_line like "*base64*")
        )
    ) or
    (
        /* PowerShell: encoded command flag — require trailing space to avoid matching
           -Encoding, -EncryptionType, -EncryptionProvider, etc. */
        (pname like "powershell*" or pname like "pwsh*") 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: buffer.from must be paired with base64 to avoid matching
           general Buffer usage; atob is always base64 */
        pname like "node*" and
        (
            (command_line like "*buffer.from*" and command_line like "*base64*") or
            command_line like "*atob(*"
        )
    ) or
    (
        /* Deno: eval( (not eval/evaluate/evaluation), atob, or buffer+base64 */
        pname like "deno*" 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
| KEEP *
'''

[[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/"