sigma-rules/rules/windows/defense_evasion_disable_posh_scriptblocklogging.toml

[metadata]
creation_date = "2022/01/31"
maturity = "production"
updated_date = "2022/05/09"

[rule]
author = ["Elastic"]
description = """
Identifies attempts to disable PowerShell Script Block Logging via registry modification. Attackers may disable this
logging to conceal their activities in the host and evade detection.
"""
from = "now-9m"
index = ["winlogbeat-*", "logs-endpoint.events.*", "logs-windows.*"]
language = "eql"
license = "Elastic License v2"
name = "PowerShell Script Block Logging Disabled"
note = """## Triage and analysis

### Investigating PowerShell Script Block Logging Disabled

PowerShell is one of the main tools system administrators use for automation, report routines, and other tasks, making
it available in various environments and creating an attractive way for attackers to execute code.

PowerShell Script Block Logging is a feature of PowerShell that records the content of all script blocks that it
processes, giving defenders visibility of PowerShell scripts and sequences of executed commands.

#### Possible investigation steps

- Identify the user account that performed the action and whether it should perform this kind of action.
- Investigate the process 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.
- Investigate other alerts associated with the user/host during the past 48 hours.
- Check whether it makes sense for the user to use PowerShell to complete tasks.
- Investigate if PowerShell scripts were run after logging was disabled.

### False positive analysis

- This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.

### Related rules

- PowerShell Suspicious Discovery Related Windows API Functions - 61ac3638-40a3-44b2-855a-985636ca985e
- PowerShell Keylogging Script - bd2c86a0-8b61-4457-ab38-96943984e889
- PowerShell Suspicious Script with Audio Capture Capabilities - 2f2f4939-0b34-40c2-a0a3-844eb7889f43
- Potential Process Injection via PowerShell - 2e29e96a-b67c-455a-afe4-de6183431d0d
- Suspicious .NET Reflection via PowerShell - e26f042e-c590-4e82-8e05-41e81bd822ad
- PowerShell Suspicious Payload Encoded and Compressed - 81fe9dc6-a2d7-4192-a2d8-eed98afc766a
- PowerShell Suspicious Script with Screenshot Capabilities - 959a7353-1129-4aa7-9084-30746b256a70

### Response and remediation

- Initiate the incident response process based on the outcome of the triage.
- Isolate the involved hosts to prevent further post-compromise behavior.
- Review the privileges assigned to the involved users to ensure that the least privilege principle is being followed.
- Restrict PowerShell usage outside of IT and engineering business units using GPOs, AppLocker, Intune, or similar software.
- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and
malware components.
- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
- 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).

## Setup

The 'PowerShell Script Block Logging' logging policy must be configured (Enable).

Steps to implement the logging policy with with Advanced Audit Configuration:

```
Computer Configuration >
Administrative Templates >
Windows PowerShell >
Turn on PowerShell Script Block Logging (Enable)
```

Steps to implement the logging policy via registry:

```
reg add "hklm\\SOFTWARE\\Policies\\Microsoft\\Windows\\PowerShell\\ScriptBlockLogging" /v EnableScriptBlockLogging /t REG_DWORD /d 1
```

If 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.
"""
references = [
    "https://admx.help/?Category=Windows_10_2016&Policy=Microsoft.Policies.PowerShell::EnableScriptBlockLogging",
]
risk_score = 47
rule_id = "818e23e6-2094-4f0e-8c01-22d30f3506c6"
severity = "medium"
tags = ["Elastic", "Host", "Windows", "Threat Detection", "Defense Evasion"]
timestamp_override = "event.ingested"
type = "eql"

query = '''
registry where event.type == "change" and
    registry.path :
        "HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows\\PowerShell\\ScriptBlockLogging\\EnableScriptBlockLogging"
    and registry.data.strings : ("0", "0x00000000")
'''


[[rule.threat]]
framework = "MITRE ATT&CK"
[[rule.threat.technique]]
id = "T1562"
name = "Impair Defenses"
reference = "https://attack.mitre.org/techniques/T1562/"
[[rule.threat.technique.subtechnique]]
id = "T1562.002"
name = "Disable Windows Event Logging"
reference = "https://attack.mitre.org/techniques/T1562/002/"



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