Bypass UAC via Event Viewer

[metadata]
creation_date = "2020/03/17"
integration = ["endpoint", "windows", "system", "m365_defender", "sentinel_one_cloud_funnel", "crowdstrike"]
maturity = "production"
updated_date = "2026/05/03"

[rule]
author = ["Elastic"]
description = """
Identifies User Account Control (UAC) bypass via eventvwr.exe. Attackers bypass UAC to stealthily execute code with
elevated permissions.
"""
from = "now-9m"
index = [
    "endgame-*",
    "logs-crowdstrike.fdr*",
    "logs-endpoint.events.process-*",
    "logs-m365_defender.event-*",
    "logs-sentinel_one_cloud_funnel.*",
    "logs-system.security*",
    "logs-windows.forwarded*",
    "logs-windows.sysmon_operational-*",
    "winlogbeat-*",
]
language = "eql"
license = "Elastic License v2"
name = "Bypass UAC via Event Viewer"
risk_score = 73
rule_id = "31b4c719-f2b4-41f6-a9bd-fce93c2eaf62"
severity = "high"
tags = [
    "Domain: Endpoint",
    "OS: Windows",
    "Use Case: Threat Detection",
    "Tactic: Privilege Escalation",
    "Resources: Investigation Guide",
    "Data Source: Elastic Endgame",
    "Data Source: Elastic Defend",
    "Data Source: Microsoft Defender XDR",
    "Data Source: Windows Security Event Logs",
    "Data Source: Sysmon",
    "Data Source: SentinelOne",
    "Data Source: Crowdstrike",
]
timestamp_override = "event.ingested"
type = "eql"

query = '''
process where host.os.type == "windows" and event.type == "start" and
  process.parent.name : "eventvwr.exe" and
  not process.executable : (
        "?:\\Windows\\SysWOW64\\mmc.exe",
        "?:\\Windows\\System32\\mmc.exe",
        "?:\\Windows\\SysWOW64\\WerFault.exe",
        "?:\\Windows\\System32\\WerFault.exe",

        /* Crowdstrike specific exclusion as it uses NT Object paths */
        "\\Device\\HarddiskVolume*\\Windows\\Sys?????\\mmc.exe",
        "\\Device\\HarddiskVolume*\\Windows\\Sys?????\\WerFault.exe"
  )
'''

note = """## Triage and analysis

### Investigating Bypass UAC via Event Viewer

#### Possible investigation steps

- What did Event Viewer launch in the alert?
  - Focus: alert time, host/user scope, `process.parent.executable`, `process.executable`, `process.command_line`, and integrity level.
  - Implication: escalate when eventvwr.exe launches an unexpected high-integrity child or script/LOLBIN command instead of the normal console or error-reporting helper; lower suspicion only when path normalization proves helper behavior or fields match controlled UAC testing.

- Does the child payload identity and command line fit helper behavior or payload execution?
  - Focus: `process.executable`, `process.hash.sha256`, `process.code_signature.subject_name`, `process.code_signature.trusted`, and `process.command_line`.
  - Hint: use `process.pe.original_file_name` when path, filename, or signer conflicts suggest masquerading.
  - Implication: escalate when the child is unsigned, rare, user-writable, signer-mismatched, or runs PowerShell, cmd.exe, rundll32.exe, mshta.exe, wscript.exe, regsvr32.exe, remote retrieval, encoded content, or admin-path writes; lower suspicion only when identity, signer, hash history, and command intent fit controlled testing or helper behavior.

- What started Event Viewer, and did the session fit an interactive admin task?
  - Focus: recover the Event Viewer start using `host.id` + `process.parent.entity_id`, then review executable, command line, and logon type. $investigate_0
  - Hint: if `process.parent.entity_id` is absent, use `host.id` + `process.parent.pid` in a tight `@timestamp` window; PID-only recovery is weaker. Inspect `process.Ext.ancestry` only when direct lineage is incomplete.
  - Implication: escalate when Office, browser, archive, scripting, RMM, or remote/noninteractive activity launched Event Viewer; lower suspicion only when launcher and session also support controlled testing or helper behavior. Routine Event Viewer use should open Microsoft Management Console, not an arbitrary child.

- Is there corroborating current-user mscfile hijack evidence when process evidence stays suspicious?
  - Focus: if registry telemetry exists, review current-user mscfile shell-open command content, creator/deleter process, and timing; HKCU may render as HKEY_USERS\\<user SID>\\Software\\Classes\\mscfile\\shell\\open\\command.
  - Hint: use this as corroboration, not as a prerequisite for escalation. Missing registry telemetry is unresolved, not benign; absence of the key after the alert can mean cleanup.
  - Implication: escalate or raise confidence when the value points to the alert child, a script interpreter, a temp/user path, or was created or removed around the alert; lower suspicion only when artifact evidence fits the same confirmed test or helper behavior already supported by process evidence.

- What did the elevated child do next?
  - Focus: child process events where `process.parent.entity_id` matches `process.entity_id`; review executable, command line, and integrity level. $investigate_1
  - Hint: prefer entity-ID matches; if only PID matches are available, keep them tightly anchored to `@timestamp`.
  - Implication: escalate when the elevated child spawns shells, discovery, credential tools, droppers, installers, persistence helpers, or network-capable tooling; do not close on absent follow-on children when the original command, lineage, or mscfile evidence remains suspicious.

- Does the same Event Viewer payload pattern recur beyond this host?
  - Range: run only when local process, command, artifact, or lineage evidence remains suspicious or unresolved.
  - Focus: `process.hash.sha256`, stable command-line fragments, and `process.executable`, scoped by host and user.
    - $investigate_2
    - $investigate_3
  - Implication: broaden when the same payload or Event Viewer child pattern appears for unrelated hosts or users; keep locally scoped when recurrence is limited to the same confirmed test cohort and no contradictory local evidence remains.

- Based on the evidence gathered, what disposition is supported?
  - Escalate on strong local abuse signals across child behavior, payload identity, command intent, launcher/session, mscfile artifacts, follow-on children, or scope; close only when process evidence and recovery prove helper normalization or controlled testing; preserve evidence and escalate when registry corroboration is unavailable or evidence is mixed.

### False positive analysis

- This behavior is an operational anti-pattern. Realistic benign paths are controlled UAC testing or a sensor/path-normalization miss for expected Microsoft Management Console (mmc.exe) or Windows Error Reporting (WerFault.exe) child activity. Confirm identity, launcher/session context, command line, and any recovered mscfile artifact support the same benign explanation; if any dimension contradicts it, do not close as benign.
- Build exceptions from the minimum confirmed pattern: stable child hash or signer, exact Event Viewer parent-child relationship, bounded `user.id` and `host.id`, and test or normalization evidence. Avoid exceptions on `process.parent.name`, `process.name`, or `user.name` alone.

### Response and remediation

- If confirmed benign, document the exact evidence that resolved the alert, reverse temporary containment, and keep any exception scoped to the confirmed child identity, parent-child pattern, and host/user cohort.
- If suspicious but unconfirmed, preserve the alert, process event exports, Event Viewer parent and child entity IDs, command lines, hashes/signers, recovered mscfile value/history, child process tree, and process-scoped file or network indicators when available.
- After preservation, apply reversible containment tied to the findings, such as endpoint isolation for non-critical hosts or temporary egress restrictions for confirmed suspicious destinations. Weigh host criticality before isolation.
- If confirmed malicious, preserve the confirmed hashes/domains/destinations and elevated child process details, then isolate the host as needed, block confirmed malicious indicators, and suspend or terminate malicious processes only after recording their evidence.
- Eradicate only the artifacts found during triage: remove malicious payloads, restore the current-user mscfile handler to the expected mmc.exe behavior or remove the malicious override, clean related persistence, and remediate the entry vector that launched Event Viewer.
- Reset credentials or disable accounts only when process/session evidence shows credential exposure, explicit misuse, or attacker use of the affected `user.id`.
- After eradication, reduce repeat exposure by reviewing local administrator membership, using the highest feasible UAC prompt level, and patching affected Windows builds.
"""

setup = """## Setup

This rule is designed for data generated by [Elastic Defend](https://www.elastic.co/security/endpoint-security), which provides native endpoint detection and response, along with event enrichments designed to work with our detection rules.

Setup instructions: https://ela.st/install-elastic-defend

### Additional data sources

This rule also supports the following third-party data sources. For setup instructions, refer to the links below:

- [CrowdStrike](https://ela.st/crowdstrike-integration)
- [Microsoft Defender XDR](https://ela.st/m365-defender)
- [SentinelOne Cloud Funnel](https://ela.st/sentinel-one-cloud-funnel)
- [Sysmon Event ID 1 - Process Creation](https://ela.st/sysmon-event-1-setup)
- [Windows Process Creation Logs](https://ela.st/audit-process-creation)
"""

[rule.investigation_fields]
field_names = [
    "@timestamp",
    "host.id",
    "user.id",
    "process.entity_id",
    "process.pid",
    "process.name",
    "process.executable",
    "process.command_line",
    "process.hash.sha256",
    "process.code_signature.trusted",
    "process.Ext.token.integrity_level_name",
    "process.parent.entity_id",
    "process.parent.pid",
    "process.parent.name",
    "process.parent.executable",
]

[transform]

[[transform.investigate]]
label = "Event Viewer parent process event"
description = ""
providers = [
  [
    { excluded = false, field = "event.category", queryType = "phrase", value = "process", valueType = "string" },
    { excluded = false, field = "host.id", queryType = "phrase", value = "{{host.id}}", valueType = "string" },
    { excluded = false, field = "process.entity_id", queryType = "phrase", value = "{{process.parent.entity_id}}", valueType = "string" }
  ],
  [
    { excluded = false, field = "event.category", queryType = "phrase", value = "process", valueType = "string" },
    { excluded = false, field = "event.type", queryType = "phrase", value = "start", valueType = "string" },
    { excluded = false, field = "host.id", queryType = "phrase", value = "{{host.id}}", valueType = "string" },
    { excluded = false, field = "process.pid", queryType = "phrase", value = "{{process.parent.pid}}", valueType = "string" }
  ]
]
relativeFrom = "now-1h"
relativeTo = "now"

[[transform.investigate]]
label = "Process starts from the elevated child"
description = ""
providers = [
  [
    { excluded = false, field = "event.category", queryType = "phrase", value = "process", valueType = "string" },
    { excluded = false, field = "event.type", queryType = "phrase", value = "start", valueType = "string" },
    { excluded = false, field = "host.id", queryType = "phrase", value = "{{host.id}}", valueType = "string" },
    { excluded = false, field = "process.parent.entity_id", queryType = "phrase", value = "{{process.entity_id}}", valueType = "string" }
  ],
  [
    { excluded = false, field = "event.category", queryType = "phrase", value = "process", valueType = "string" },
    { excluded = false, field = "event.type", queryType = "phrase", value = "start", valueType = "string" },
    { excluded = false, field = "host.id", queryType = "phrase", value = "{{host.id}}", valueType = "string" },
    { excluded = false, field = "process.parent.pid", queryType = "phrase", value = "{{process.pid}}", valueType = "string" }
  ]
]
relativeFrom = "now"
relativeTo = "now"

[[transform.investigate]]
label = "Recent process starts with the same child identity"
description = ""
providers = [
  [
    { excluded = false, field = "event.category", queryType = "phrase", value = "process", valueType = "string" },
    { excluded = false, field = "event.type", queryType = "phrase", value = "start", valueType = "string" },
    { excluded = false, field = "process.hash.sha256", queryType = "phrase", value = "{{process.hash.sha256}}", valueType = "string" }
  ],
  [
    { excluded = false, field = "event.category", queryType = "phrase", value = "process", valueType = "string" },
    { excluded = false, field = "event.type", queryType = "phrase", value = "start", valueType = "string" },
    { excluded = false, field = "process.executable", queryType = "phrase", value = "{{process.executable}}", valueType = "string" }
  ]
]
relativeFrom = "now-48h/h"
relativeTo = "now"

[[transform.investigate]]
label = "Alerts associated with the user or host"
description = ""
providers = [
  [
    { excluded = false, field = "event.kind", queryType = "phrase", value = "signal", valueType = "string" },
    { excluded = false, field = "user.id", queryType = "phrase", value = "{{user.id}}", valueType = "string" }
  ],
  [
    { excluded = false, field = "event.kind", queryType = "phrase", value = "signal", valueType = "string" },
    { excluded = false, field = "host.id", queryType = "phrase", value = "{{host.id}}", valueType = "string" }
  ]
]
relativeFrom = "now-48h/h"
relativeTo = "now"

[[rule.threat]]
framework = "MITRE ATT&CK"

[[rule.threat.technique]]
id = "T1548"
name = "Abuse Elevation Control Mechanism"
reference = "https://attack.mitre.org/techniques/T1548/"

[[rule.threat.technique.subtechnique]]
id = "T1548.002"
name = "Bypass User Account Control"
reference = "https://attack.mitre.org/techniques/T1548/002/"

[rule.threat.tactic]
id = "TA0004"
name = "Privilege Escalation"
reference = "https://attack.mitre.org/tactics/TA0004/"

[[rule.threat]]
framework = "MITRE ATT&CK"

[[rule.threat.technique]]
id = "T1548"
name = "Abuse Elevation Control Mechanism"
reference = "https://attack.mitre.org/techniques/T1548/"

[[rule.threat.technique.subtechnique]]
id = "T1548.002"
name = "Bypass User Account Control"
reference = "https://attack.mitre.org/techniques/T1548/002/"

[rule.threat.tactic]
id = "TA0005"
name = "Defense Evasion"
reference = "https://attack.mitre.org/tactics/TA0005/"