sigma-rules/rules/windows/persistence_startup_folder_scripts.toml

[metadata]
creation_date = "2020/11/18"
maturity = "production"
updated_date = "2022/11/04"
min_stack_comments = "New fields added: required_fields, related_integrations, setup"
min_stack_version = "8.3.0"

[rule]
author = ["Elastic"]
description = """
Identifies script engines creating files in the Startup folder, or the creation of script files in the Startup folder.
Adversaries may abuse this technique to maintain persistence in an environment.
"""
from = "now-9m"
index = ["winlogbeat-*", "logs-endpoint.events.*", "logs-windows.*"]
language = "eql"
license = "Elastic License v2"
name = "Persistent Scripts in the Startup Directory"
note = """## Triage and analysis

### Investigating Persistent Scripts in the Startup Directory

The Windows Startup folder is a special folder in Windows. Programs added to this folder are executed during account
logon, without user interaction, providing an excellent way for attackers to maintain persistence.

This rule looks for shortcuts created by wscript.exe or cscript.exe, or js/vbs scripts created by any process.

> **Note**:
> This investigation guide uses the [Osquery Markdown Plugin](https://www.elastic.co/guide/en/security/master/invest-guide-run-osquery.html) introduced in Elastic stack version 8.5.0. Older Elastic stacks versions will see unrendered markdown in this guide.

#### Possible investigation steps

- 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.
- Validate the activity is not related to planned patches, updates, network administrator activity, or legitimate
software installations.
- Assess whether this behavior is prevalent in the environment by looking for similar occurrences across hosts.
- Examine the host for derived artifacts that indicates suspicious activities:
  - Analyze the file using a private sandboxed analysis system.
  - Observe and collect information about the following activities in both the sandbox and the alert subject host:
    - Attempts to contact external domains and addresses.
      - Use the Elastic Defend network events to determine domains and addresses contacted by the subject process by
      filtering by the process' `process.entity_id`.
      - Examine the DNS cache for suspicious or anomalous entries.
        - !{osquery{"query":"SELECT * FROM dns_cache", "label":"Osquery - Retrieve DNS Cache"}}
    - Use the Elastic Defend registry events to examine registry keys accessed, modified, or created by the related
    processes in the process tree.
    - Examine the host services for suspicious or anomalous entries.
      - !{osquery{"query":"SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services","label":"Osquery - Retrieve All Services"}}
      - !{osquery{"query":"SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services WHERE NOT (user_account LIKE \"%LocalSystem\" OR user_account LIKE \"%LocalService\" OR user_account LIKE \"%NetworkService\" OR user_account == null)","label":"Osquery - Retrieve Services Running on User Accounts"}}
      - !{osquery{"query":"SELECT concat('https://www.virustotal.com/gui/file/', sha1) AS VtLink, name, description, start_type, status, pid, services.path FROM services JOIN authenticode ON services.path = authenticode.path OR services.module_path = authenticode.path JOIN hash ON services.path = hash.path WHERE authenticode.result != \"trusted\"","label":"Osquery - Retrieve Service Unsigned Executables with Virustotal Link"}}
  - Retrieve the files' SHA-256 hash values using the PowerShell `Get-FileHash` cmdlet and search for the existence and
  reputation of the hashes in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.

### False positive analysis

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

### Related rules

- Suspicious Startup Shell Folder Modification - c8b150f0-0164-475b-a75e-74b47800a9ff
- Startup Folder Persistence via Unsigned Process - 2fba96c0-ade5-4bce-b92f-a5df2509da3f

### Response and remediation

- Initiate the incident response process based on the outcome of the triage.
- Isolate the involved host to prevent further post-compromise behavior.
- If the triage identified malware, search the environment for additional compromised hosts.
  - Implement temporary network rules, procedures, and segmentation to contain the malware.
  - Stop suspicious processes.
  - Immediately block the identified indicators of compromise (IoCs).
  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that
  attackers could use to reinfect the system.
- Remove and block malicious artifacts identified during triage.
- Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are
identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business
systems, and web services.
- 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

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.
"""
risk_score = 47
rule_id = "f7c4dc5a-a58d-491d-9f14-9b66507121c0"
severity = "medium"
tags = ["Elastic", "Host", "Windows", "Threat Detection", "Persistence", "Investigation Guide"]
timestamp_override = "event.ingested"
type = "eql"

query = '''
file where event.type != "deletion" and user.domain != "NT AUTHORITY" and

  /* detect shortcuts created by wscript.exe or cscript.exe */
  (file.path : "C:\\*\\Programs\\Startup\\*.lnk" and
     process.name : ("wscript.exe", "cscript.exe")) or

  /* detect vbs or js files created by any process */
  file.path : ("C:\\*\\Programs\\Startup\\*.vbs",
               "C:\\*\\Programs\\Startup\\*.vbe",
               "C:\\*\\Programs\\Startup\\*.wsh",
               "C:\\*\\Programs\\Startup\\*.wsf",
               "C:\\*\\Programs\\Startup\\*.js")
'''


[[rule.threat]]
framework = "MITRE ATT&CK"
[[rule.threat.technique]]
id = "T1547"
name = "Boot or Logon Autostart Execution"
reference = "https://attack.mitre.org/techniques/T1547/"
[[rule.threat.technique.subtechnique]]
id = "T1547.001"
name = "Registry Run Keys / Startup Folder"
reference = "https://attack.mitre.org/techniques/T1547/001/"



[rule.threat.tactic]
id = "TA0003"
name = "Persistence"
reference = "https://attack.mitre.org/tactics/TA0003/"