Windows InstallUtil Credential Theft

SPLUNK detection rule by Michael Haag, Mauricio Velazo, Splunk · Apache-2.0

The following analytic detects instances where the Windows InstallUtil.exe binary loads `vaultcli.dll` and `Samlib.dll`. This detection leverages Sysmon EventCode 7 to identify these specific DLL loads. This activity is significant because it can indicate an attempt to execute code that bypasses application control and captures credentials using tools like Mimikatz. If confirmed malicious, this behavior could allow an attacker to steal credentials, potentially leading to unauthorized access and further compromise of the system.

name: Windows InstallUtil Credential Theft
id: ccfeddec-43ec-11ec-b494-acde48001122
version: 13
creation_date: '2021-11-12'
modification_date: '2026-05-13'
author: Michael Haag, Mauricio Velazo, Splunk
status: production
type: TTP
description: The following analytic detects instances where the Windows InstallUtil.exe binary loads `vaultcli.dll` and `Samlib.dll`. This detection leverages Sysmon EventCode 7 to identify these specific DLL loads. This activity is significant because it can indicate an attempt to execute code that bypasses application control and captures credentials using tools like Mimikatz. If confirmed malicious, this behavior could allow an attacker to steal credentials, potentially leading to unauthorized access and further compromise of the system.
data_source:
    - Sysmon EventID 7
search: '`sysmon` EventCode=7 process_name=installutil.exe loaded_file_path IN ("*\\samlib.dll", "*\\vaultcli.dll") | fillnull | stats count min(_time) as firstTime max(_time) as lastTime by Image ImageLoaded dest loaded_file loaded_file_path original_file_name process_exec process_guid process_hash process_id process_name process_path service_dll_signature_exists service_dll_signature_verified signature signature_id user_id vendor_product | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `windows_installutil_credential_theft_filter`'
how_to_implement: To successfully implement this search, you need to be ingesting logs with the process name, parent process, and module loads from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.
known_false_positives: Typically, this will not trigger because, by its very nature, InstallUtil does not require credentials. Filter as needed.
references:
    - https://gist.github.com/xorrior/bbac3919ca2aef8d924bdf3b16cce3d0
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search  dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
finding:
    title: An instance of process name [$process_name$] loading a file [$loaded_file$] was identified on endpoint- [$dest$] to potentially capture credentials in memory.
    entity:
        field: dest
        type: system
        score: 50
threat_objects:
    - field: process_name
      type: process_name
analytic_story:
    - Signed Binary Proxy Execution InstallUtil
asset_type: Endpoint
mitre_attack_id:
    - T1218.004
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1218.004/atomic_red_team/windows-sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit

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7061465b-93e7-4085-979b-cdd99c6279ba

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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