Bypass UAC via Event Viewer

Identifies User Account Control (UAC) bypass via eventvwr.exe. Attackers bypass UAC to stealthily execute code with elevated permissions.

Elastic rule (View on GitHub)

  1[metadata]
  2creation_date = "2020/03/17"
  3integration = ["endpoint", "windows", "system"]
  4maturity = "production"
  5updated_date = "2024/05/21"
  6
  7[transform]
  8[[transform.osquery]]
  9label = "Osquery - Retrieve DNS Cache"
 10query = "SELECT * FROM dns_cache"
 11
 12[[transform.osquery]]
 13label = "Osquery - Retrieve All Services"
 14query = "SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services"
 15
 16[[transform.osquery]]
 17label = "Osquery - Retrieve Services Running on User Accounts"
 18query = """
 19SELECT description, display_name, name, path, pid, service_type, start_type, status, user_account FROM services WHERE
 20NOT (user_account LIKE '%LocalSystem' OR user_account LIKE '%LocalService' OR user_account LIKE '%NetworkService' OR
 21user_account == null)
 22"""
 23
 24[[transform.osquery]]
 25label = "Osquery - Retrieve Service Unsigned Executables with Virustotal Link"
 26query = """
 27SELECT concat('https://www.virustotal.com/gui/file/', sha1) AS VtLink, name, description, start_type, status, pid,
 28services.path FROM services JOIN authenticode ON services.path = authenticode.path OR services.module_path =
 29authenticode.path JOIN hash ON services.path = hash.path WHERE authenticode.result != 'trusted'
 30"""
 31
 32
 33[rule]
 34author = ["Elastic"]
 35description = """
 36Identifies User Account Control (UAC) bypass via eventvwr.exe. Attackers bypass UAC to stealthily execute code with
 37elevated permissions.
 38"""
 39from = "now-9m"
 40index = [
 41    "winlogbeat-*",
 42    "logs-endpoint.events.process-*",
 43    "logs-windows.*",
 44    "endgame-*",
 45    "logs-system.security*",
 46]
 47language = "eql"
 48license = "Elastic License v2"
 49name = "Bypass UAC via Event Viewer"
 50note = """## Triage and analysis
 51
 52### Investigating Bypass UAC via Event Viewer
 53
 54Windows User Account Control (UAC) allows a program to elevate its privileges (tracked as low to high integrity levels) to perform a task under administrator-level permissions, possibly by prompting the user for confirmation. UAC can deny an operation under high-integrity enforcement, or allow the user to perform the action if they are in the local administrators group and enter an administrator password when prompted.
 55
 56For more information about the UAC and how it works, check the [official Microsoft docs page](https://docs.microsoft.com/en-us/windows/security/identity-protection/user-account-control/how-user-account-control-works).
 57
 58During startup, `eventvwr.exe` checks the registry value of the `HKCU\\Software\\Classes\\mscfile\\shell\\open\\command` registry key for the location of `mmc.exe`, which is used to open the `eventvwr.msc` saved console file. If the location of another binary or script is added to this registry value, it will be executed as a high-integrity process without a UAC prompt being displayed to the user. This rule detects this UAC bypass by monitoring processes spawned by `eventvwr.exe` other than `mmc.exe` and `werfault.exe`.
 59
 60> **Note**:
 61> 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.
 62
 63#### Possible investigation steps
 64
 65- 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.
 66- Investigate other alerts associated with the user/host during the past 48 hours.
 67- Inspect the host for suspicious or abnormal behavior in the alert timeframe.
 68- Investigate any abnormal behavior by the subject process such as network connections, registry or file modifications, and any spawned child processes.
 69- Examine the host for derived artifacts that indicate suspicious activities:
 70  - Analyze the process executable using a private sandboxed analysis system.
 71  - Observe and collect information about the following activities in both the sandbox and the alert subject host:
 72    - Attempts to contact external domains and addresses.
 73      - Use the Elastic Defend network events to determine domains and addresses contacted by the subject process by filtering by the process' `process.entity_id`.
 74      - Examine the DNS cache for suspicious or anomalous entries.
 75        - $osquery_0
 76    - Use the Elastic Defend registry events to examine registry keys accessed, modified, or created by the related processes in the process tree.
 77    - Examine the host services for suspicious or anomalous entries.
 78      - $osquery_1
 79      - $osquery_2
 80      - $osquery_3
 81  - 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.
 82- Investigate potentially compromised accounts. Analysts can do this by searching for login events (for example, 4624) to the target host after the registry modification.
 83
 84
 85### False positive analysis
 86
 87- This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.
 88
 89### Response and remediation
 90
 91- Initiate the incident response process based on the outcome of the triage.
 92- Isolate the involved host to prevent further post-compromise behavior.
 93- If the triage identified malware, search the environment for additional compromised hosts.
 94  - Implement temporary network rules, procedures, and segmentation to contain the malware.
 95  - Stop suspicious processes.
 96  - Immediately block the identified indicators of compromise (IoCs).
 97  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
 98- Remove and block malicious artifacts identified during triage.
 99- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
100- 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.
101- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
102- 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).
103"""
104risk_score = 73
105rule_id = "31b4c719-f2b4-41f6-a9bd-fce93c2eaf62"
106setup = """## Setup
107
108If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2,
109events will not define `event.ingested` and default fallback for EQL rules was not added until version 8.2.
110Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate
111`event.ingested` to @timestamp.
112For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html
113"""
114severity = "high"
115tags = [
116    "Domain: Endpoint",
117    "OS: Windows",
118    "Use Case: Threat Detection",
119    "Tactic: Privilege Escalation",
120    "Tactic: Defense Evasion",
121    "Resources: Investigation Guide",
122    "Data Source: Elastic Endgame",
123    "Data Source: Elastic Defend",
124]
125timestamp_override = "event.ingested"
126type = "eql"
127
128query = '''
129process where host.os.type == "windows" and event.type == "start" and
130  process.parent.name : "eventvwr.exe" and
131  not process.executable :
132            ("?:\\Windows\\SysWOW64\\mmc.exe",
133             "?:\\Windows\\System32\\mmc.exe",
134             "?:\\Windows\\SysWOW64\\WerFault.exe",
135             "?:\\Windows\\System32\\WerFault.exe")
136'''
137
138
139[[rule.threat]]
140framework = "MITRE ATT&CK"
141[[rule.threat.technique]]
142id = "T1548"
143name = "Abuse Elevation Control Mechanism"
144reference = "https://attack.mitre.org/techniques/T1548/"
145[[rule.threat.technique.subtechnique]]
146id = "T1548.002"
147name = "Bypass User Account Control"
148reference = "https://attack.mitre.org/techniques/T1548/002/"
149
150
151
152[rule.threat.tactic]
153id = "TA0004"
154name = "Privilege Escalation"
155reference = "https://attack.mitre.org/tactics/TA0004/"
156[[rule.threat]]
157framework = "MITRE ATT&CK"
158[[rule.threat.technique]]
159id = "T1548"
160name = "Abuse Elevation Control Mechanism"
161reference = "https://attack.mitre.org/techniques/T1548/"
162[[rule.threat.technique.subtechnique]]
163id = "T1548.002"
164name = "Bypass User Account Control"
165reference = "https://attack.mitre.org/techniques/T1548/002/"
166
167
168
169[rule.threat.tactic]
170id = "TA0005"
171name = "Defense Evasion"
172reference = "https://attack.mitre.org/tactics/TA0005/"

Triage and analysis

Investigating Bypass UAC via Event Viewer

Windows User Account Control (UAC) allows a program to elevate its privileges (tracked as low to high integrity levels) to perform a task under administrator-level permissions, possibly by prompting the user for confirmation. UAC can deny an operation under high-integrity enforcement, or allow the user to perform the action if they are in the local administrators group and enter an administrator password when prompted.

For more information about the UAC and how it works, check the official Microsoft docs page.

During startup, eventvwr.exe checks the registry value of the HKCU\Software\Classes\mscfile\shell\open\command registry key for the location of mmc.exe, which is used to open the eventvwr.msc saved console file. If the location of another binary or script is added to this registry value, it will be executed as a high-integrity process without a UAC prompt being displayed to the user. This rule detects this UAC bypass by monitoring processes spawned by eventvwr.exe other than mmc.exe and werfault.exe.

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.
  • Inspect the host for suspicious or abnormal behavior in the alert timeframe.
  • Investigate any abnormal behavior by the subject process such as network connections, registry or file modifications, and any spawned child processes.
  • Examine the host for derived artifacts that indicate suspicious activities:
    • Analyze the process executable 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

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

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).

Related rules

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