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Suspicious Startup Shell Folder Modification

Elastic Stack Serverless Security

Identifies suspicious startup shell folder modifications to change the default Startup directory in order to bypass detections monitoring file creation in the Windows Startup folder.

Rule type: eql

Rule indices:

  • winlogbeat-*
  • logs-endpoint.events.*
  • logs-windows.*

Severity: high

Risk score: 73

Runs every: 5m

Searches indices from: now-9m (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[Date Math format], see also Additional look-back time)

Maximum alerts per execution: 100

References: None

Tags:

  • Elastic
  • Host
  • Windows
  • Threat Detection
  • Persistence

Version: 2

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guide

Techniques used within malware and by adversaries often leverage the Windows registry to store malicious programs for
persistence. Startup shell folders are often targeted as they are not as prevalent as normal Startup folder paths so this
behavior may evade existing AV/EDR solutions. Another preference is that these programs might run with higher privileges
which can be ideal for an attacker.

  • Review the source process and related file tied to the Windows Registry entry
  • Validate the activity is not related to planned patches, updates, network administrator activity or legitimate software
    installations
  • Determine if activity is unique by validating if other machines in same organization have similar entry
  • There is a high possibility of benign legitimate programs being added to Shell folders. This activity could be based
    on new software installations, patches, or any kind of network administrator related activity. Before entering further
    investigation, this activity should be validated that is it not related to benign activity
  • Startup or Run Key Registry Modification
  • Persistent Scripts in the Startup Directory
  • Activity should first be validated as a true positive event if so then immediate response should be taken to review,
    investigate and potentially isolate activity to prevent further post-compromise behavior
  • The respective binary or program tied to this persistence method should be further analyzed and reviewed to understand
    it's behavior and capabilities
  • Since this activity is considered post-exploitation behavior, it's important to understand how the behavior was first
    initialized such as through a macro-enabled document that was attached in a phishing email. By understanding the source
    of the attack, this information can then be used to search for similar indicators on other machines in the same environment.

Rule query

registry where
 registry.path : (
     "HKLM\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\User Shell Folders\\Common Startup",
     "HKLM\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Shell Folders\\Common Startup",
     "HKEY_USERS\\*\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\User Shell Folders\\Startup",
     "HKEY_USERS\\*\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Shell Folders\\Startup"
     ) and
  registry.data.strings != null and
  /* Normal Startup Folder Paths */
  not registry.data.strings : (
           "C:\\ProgramData\\Microsoft\\Windows\\Start Menu\\Programs\\Startup",
           "%ProgramData%\\Microsoft\\Windows\\Start Menu\\Programs\\Startup",
           "%USERPROFILE%\\AppData\\Roaming\\Microsoft\\Windows\\Start Menu\\Programs\\Startup",
           "C:\\Users\\*\\AppData\\Roaming\\Microsoft\\Windows\\Start Menu\\Programs\\Startup"
           )

Framework: MITRE ATT&CKTM