Potential Privilege Escalation via InstallerFileTakeOver

Identifies a potential exploitation of InstallerTakeOver (CVE-2021-41379) default PoC execution. Successful exploitation allows an unprivileged user to escalate privileges to SYSTEM.

Elastic rule (View on GitHub)

  1[metadata]
  2creation_date = "2021/11/25"
  3integration = ["endpoint"]
  4maturity = "production"
  5min_stack_comments = "New fields added: required_fields, related_integrations, setup"
  6min_stack_version = "8.3.0"
  7updated_date = "2023/10/23"
  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 a potential exploitation of InstallerTakeOver (CVE-2021-41379) default PoC execution. Successful exploitation
 39allows an unprivileged user to escalate privileges to SYSTEM.
 40"""
 41from = "now-9m"
 42index = ["logs-endpoint.events.*"]
 43language = "eql"
 44license = "Elastic License v2"
 45name = "Potential Privilege Escalation via InstallerFileTakeOver"
 46note = """## Triage and analysis
 47
 48### Investigating Potential Privilege Escalation via InstallerFileTakeOver
 49
 50InstallerFileTakeOver is a weaponized escalation of privilege proof of concept (EoP PoC) to the CVE-2021-41379 vulnerability. Upon successful exploitation, an unprivileged user will escalate privileges to SYSTEM/NT AUTHORITY.
 51
 52This rule detects the default execution of the PoC, which overwrites the `elevation_service.exe` DACL and copies itself to the location to escalate privileges. An attacker is able to still take over any file that is not in use (locked), which is outside the scope of this rule.
 53
 54> **Note**:
 55> 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.
 56
 57#### Possible investigation steps
 58
 59- 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.
 60- Investigate other alerts associated with the user/host during the past 48 hours.
 61- Look for additional processes spawned by the process, command lines, and network communications.
 62- Assess whether this behavior is prevalent in the environment by looking for similar occurrences across hosts.
 63- Examine the host for derived artifacts that indicate suspicious activities:
 64  - Analyze the file using a private sandboxed analysis system.
 65  - Observe and collect information about the following activities in both the sandbox and the alert subject host:
 66    - Attempts to contact external domains and addresses.
 67      - Use the Elastic Defend network events to determine domains and addresses contacted by the subject process by filtering by the process' `process.entity_id`.
 68      - Examine the DNS cache for suspicious or anomalous entries.
 69        - $osquery_0
 70    - Use the Elastic Defend registry events to examine registry keys accessed, modified, or created by the related processes in the process tree.
 71    - Examine the host services for suspicious or anomalous entries.
 72      - $osquery_1
 73      - $osquery_2
 74      - $osquery_3
 75  - 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.
 76- Investigate potentially compromised accounts. Analysts can do this by searching for login events (for example, 4624) to the target host after the registry modification.
 77
 78### False positive analysis
 79
 80- Verify whether a digital signature exists in the executable, and if it is valid.
 81
 82### Related rules
 83
 84- Suspicious DLL Loaded for Persistence or Privilege Escalation - bfeaf89b-a2a7-48a3-817f-e41829dc61ee
 85
 86### Response and remediation
 87
 88- Initiate the incident response process based on the outcome of the triage.
 89- Isolate the involved host to prevent further post-compromise behavior.
 90- If the triage identified malware, search the environment for additional compromised hosts.
 91  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 92  - Stop suspicious processes.
 93  - Immediately block the identified indicators of compromise (IoCs).
 94  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 95- Remove and block malicious artifacts identified during triage.
 96- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
 97- 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.
 98- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
 99- 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).
100
101"""
102references = ["https://github.com/klinix5/InstallerFileTakeOver"]
103risk_score = 73
104rule_id = "58c6d58b-a0d3-412d-b3b8-0981a9400607"
105setup="""
106
107If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2,
108events will not define `event.ingested` and default fallback for EQL rules was not added until version 8.2.
109Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate
110`event.ingested` to @timestamp.
111For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html
112"""
113severity = "high"
114tags = ["Domain: Endpoint", "OS: Windows", "Use Case: Threat Detection", "Tactic: Privilege Escalation", "Resources: Investigation Guide", "Use Case: Vulnerability", "Data Source: Elastic Defend"]
115timestamp_override = "event.ingested"
116type = "eql"
117
118query = '''
119process where host.os.type == "windows" and event.type == "start" and
120    process.Ext.token.integrity_level_name : "System" and
121    (
122      (process.name : "elevation_service.exe" and
123       not process.pe.original_file_name == "elevation_service.exe") or
124      
125      (process.name : "elevation_service.exe" and
126       not process.code_signature.trusted == true) or
127
128      (process.parent.name : "elevation_service.exe" and
129       process.name : ("rundll32.exe", "cmd.exe", "powershell.exe"))
130    ) and
131    not
132    (
133      process.name : "elevation_service.exe" and process.code_signature.trusted == true and
134      process.pe.original_file_name == null
135    )
136'''
137
138
139[[rule.threat]]
140framework = "MITRE ATT&CK"
141[[rule.threat.technique]]
142id = "T1068"
143name = "Exploitation for Privilege Escalation"
144reference = "https://attack.mitre.org/techniques/T1068/"
145
146
147[rule.threat.tactic]
148id = "TA0004"
149name = "Privilege Escalation"
150reference = "https://attack.mitre.org/tactics/TA0004/"

Triage and analysis

Investigating Potential Privilege Escalation via InstallerFileTakeOver

InstallerFileTakeOver is a weaponized escalation of privilege proof of concept (EoP PoC) to the CVE-2021-41379 vulnerability. Upon successful exploitation, an unprivileged user will escalate privileges to SYSTEM/NT AUTHORITY.

This rule detects the default execution of the PoC, which overwrites the elevation_service.exe DACL and copies itself to the location to escalate privileges. An attacker is able to still take over any file that is not in use (locked), which is outside the scope of this rule.

Note: This investigation guide uses the Osquery Markdown Plugin introduced in Elastic Stack version 8.5.0. Older Elastic Stack versions will display 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.
  • Look for additional processes spawned by the process, command lines, and network communications.
  • Assess whether this behavior is prevalent in the environment by looking for similar occurrences across hosts.
  • Examine the host for derived artifacts that indicate 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_0
      • 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_1
        • $osquery_2
        • $osquery_3
    • 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.
  • Investigate potentially compromised accounts. Analysts can do this by searching for login events (for example, 4624) to the target host after the registry modification.

False positive analysis

  • Verify whether a digital signature exists in the executable, and if it is valid.
  • Suspicious DLL Loaded for Persistence or Privilege Escalation - bfeaf89b-a2a7-48a3-817f-e41829dc61ee

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.
  • Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
  • 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.
  • 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).

References

Related rules

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