Suspicious Startup Shell Folder Modification

  1[metadata]
  2creation_date = "2021/03/15"
  3integration = ["endpoint"]
  4maturity = "production"
  5updated_date = "2024/03/28"
  6min_stack_comments = "New fields added: required_fields, related_integrations, setup"
  7min_stack_version = "8.3.0"
  8
  9[transform]
 10[[transform.osquery]]
 11label = "Osquery - Retrieve DNS Cache"
 12query = "SELECT * FROM dns_cache"
 13
 14[[transform.osquery]]
 15label = "Osquery - Retrieve All Services"
 16query = "SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services"
 17
 18[[transform.osquery]]
 19label = "Osquery - Retrieve Services Running on User Accounts"
 20query = """
 21SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services WHERE
 22NOT (user_account LIKE '%LocalSystem' OR user_account LIKE '%LocalService' OR user_account LIKE '%NetworkService' OR
 23user_account == null)
 24"""
 25
 26[[transform.osquery]]
 27label = "Osquery - Retrieve Service Unsigned Executables with Virustotal Link"
 28query = """
 29SELECT concat('https://www.virustotal.com/gui/file/', sha1) AS VtLink, name, description, start_type, status, pid,
 30services.path FROM services JOIN authenticode ON services.path = authenticode.path OR services.module_path =
 31authenticode.path JOIN hash ON services.path = hash.path WHERE authenticode.result != 'trusted'
 32"""
 33
 34
 35[rule]
 36author = ["Elastic"]
 37description = """
 38Identifies suspicious startup shell folder modifications to change the default Startup directory in order to bypass
 39detections monitoring file creation in the Windows Startup folder.
 40"""
 41from = "now-9m"
 42index = ["logs-endpoint.events.registry-*", "endgame-*", "logs-windows.sysmon_operational-*"]
 43language = "eql"
 44license = "Elastic License v2"
 45name = "Suspicious Startup Shell Folder Modification"
 46note = """## Triage and analysis
 47
 48### Investigating Suspicious Startup Shell Folder Modification
 49
 50Techniques 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. These programs may also run with higher privileges which can be ideal for an attacker.
 51
 52> **Note**:
 53> 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 Stack versions will display unrendered Markdown in this guide.
 54
 55#### Possible investigation steps
 56
 57- 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.
 58- Review the source process and related file tied to the Windows Registry entry.
 59- Validate if the activity is not related to planned patches, updates, network administrator activity, or legitimate software installations.
 60- Assess whether this behavior is prevalent in the environment by looking for similar occurrences across hosts.
 61- Examine the host for derived artifacts that indicate suspicious activities:
 62  - Analyze the file using a private sandboxed analysis system.
 63  - Observe and collect information about the following activities in both the sandbox and the alert subject host:
 64    - Attempts to contact external domains and addresses.
 65      - Use the Elastic Defend network events to determine domains and addresses contacted by the subject process by filtering by the process' `process.entity_id`.
 66      - Examine the DNS cache for suspicious or anomalous entries.
 67        - $osquery_0
 68    - Use the Elastic Defend registry events to examine registry keys accessed, modified, or created by the related processes in the process tree.
 69    - Examine the host services for suspicious or anomalous entries.
 70      - $osquery_1
 71      - $osquery_2
 72      - $osquery_3
 73  - 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.
 74- Investigate potentially compromised accounts. Analysts can do this by searching for login events (for example, 4624) to the target host after the registry modification.
 75
 76### False positive analysis
 77
 78- 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 other network administrator activity. Before undertaking further investigation, it should be verified that this activity is not benign.
 79
 80### Related rules
 81
 82- Startup or Run Key Registry Modification - 97fc44d3-8dae-4019-ae83-298c3015600f
 83- Persistent Scripts in the Startup Directory - f7c4dc5a-a58d-491d-9f14-9b66507121c0
 84
 85### Response and remediation
 86
 87- Initiate the incident response process based on the outcome of the triage.
 88- Isolate the involved host to prevent further post-compromise behavior.
 89- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 90- If the malicious file was delivered via phishing:
 91  - Block the email sender from sending future emails.
 92  - Block the malicious web pages.
 93  - Remove emails from the sender from mailboxes.
 94  - Consider improvements to the security awareness program.
 95- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
 96- 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).
 97"""
 98risk_score = 73
 99rule_id = "c8b150f0-0164-475b-a75e-74b47800a9ff"
100severity = "high"
101tags = ["Domain: Endpoint", "OS: Windows", "Use Case: Threat Detection", "Tactic: Persistence", "Tactic: Defense Evasion", "Resources: Investigation Guide", "Data Source: Elastic Endgame", "Data Source: Elastic Defend", "Data Source: Sysmon"]
102timestamp_override = "event.ingested"
103type = "eql"
104
105query = '''
106registry where host.os.type == "windows" and
107 registry.path : (
108     "HKLM\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\User Shell Folders\\Common Startup",
109     "HKLM\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Shell Folders\\Common Startup",
110     "HKEY_USERS\\*\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\User Shell Folders\\Startup",
111     "HKEY_USERS\\*\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Shell Folders\\Startup",
112     "HKU\\*\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\User Shell Folders\\Startup",
113     "HKU\\*\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Shell Folders\\Startup",
114     "\\REGISTRY\\MACHINE\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\User Shell Folders\\Common Startup",
115     "\\REGISTRY\\MACHINE\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Shell Folders\\Common Startup",
116     "\\REGISTRY\\USER\\*\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\User Shell Folders\\Startup",
117     "\\REGISTRY\\USER\\*\\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Shell Folders\\Startup"
118     ) and
119  registry.data.strings != null and
120  /* Normal Startup Folder Paths */
121  not registry.data.strings : (
122           "C:\\ProgramData\\Microsoft\\Windows\\Start Menu\\Programs\\Startup",
123           "%ProgramData%\\Microsoft\\Windows\\Start Menu\\Programs\\Startup",
124           "%USERPROFILE%\\AppData\\Roaming\\Microsoft\\Windows\\Start Menu\\Programs\\Startup",
125           "C:\\Users\\*\\AppData\\Roaming\\Microsoft\\Windows\\Start Menu\\Programs\\Startup"
126           )
127'''
128
129
130[[rule.threat]]
131framework = "MITRE ATT&CK"
132[[rule.threat.technique]]
133id = "T1547"
134name = "Boot or Logon Autostart Execution"
135reference = "https://attack.mitre.org/techniques/T1547/"
136[[rule.threat.technique.subtechnique]]
137id = "T1547.001"
138name = "Registry Run Keys / Startup Folder"
139reference = "https://attack.mitre.org/techniques/T1547/001/"
140
141
142
143[rule.threat.tactic]
144id = "TA0003"
145name = "Persistence"
146reference = "https://attack.mitre.org/tactics/TA0003/"
147
148
149
150[[rule.threat]]
151framework = "MITRE ATT&CK"
152[[rule.threat.technique]]
153id = "T1112"
154name = "Modify Registry"
155reference = "https://attack.mitre.org/techniques/T1112/"
156
157[rule.threat.tactic]
158id = "TA0005"
159name = "Defense Evasion"
160reference = "https://attack.mitre.org/tactics/TA0005/"