Name:Windows PowerShell Add Module to Global Assembly Cache id:3fc16961-97e5-4a5b-a079-e4ab0d9763eb version:3 date:2024-09-30 author:Michael Haag, Splunk status:production type:TTP Description:The following analytic detects the addition of a DLL to the Windows Global Assembly Cache (GAC) using PowerShell. It leverages PowerShell Script Block Logging to identify commands containing "system.enterpriseservices.internal.publish". This activity is significant because adding a DLL to the GAC allows it to be shared across multiple applications, potentially enabling an adversary to execute malicious code system-wide. If confirmed malicious, this could lead to widespread code execution, privilege escalation, and persistent access across the operating system, posing a severe security risk. Data_source:
-Powershell Script Block Logging 4104
search:`powershell` EventCode=4104 ScriptBlockText IN("*system.enterpriseservices.internal.publish*") | stats count min(_time) as firstTime max(_time) as lastTime by EventCode ScriptBlockText Computer user_id | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `windows_powershell_add_module_to_global_assembly_cache_filter`
how_to_implement:To successfully implement this analytic, you will need to enable PowerShell Script Block Logging on some or all endpoints. Additional setup here https://docs.splunk.com/Documentation/UBA/5.0.4.1/GetDataIn/AddPowerShell#Configure_module_logging_for_PowerShell. known_false_positives:False positives may be present based on developers or third party utilities adding items to the GAC. References: -https://www.microsoft.com/en-us/security/blog/2022/12/12/iis-modules-the-evolution-of-web-shells-and-how-to-detect-them/ -https://www.microsoft.com/en-us/security/blog/2022/07/26/malicious-iis-extensions-quietly-open-persistent-backdoors-into-servers/ drilldown_searches: name:'View the detection results for - "$Computer$"' search:'%original_detection_search% | search Computer = "$Computer$"' earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' name:'View risk events for the last 7 days for - "$Computer$"' search:'| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$Computer$") starthoursago=168 | 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:'$info_min_time$' latest_offset:'$info_max_time$' tags: analytic_story: - 'IIS Components' asset_type:Endpoint confidence:80 impact:80 message:PowerShell was used to install a module to the Global Assembly Cache on $Computer$. mitre_attack_id: - 'T1505' - 'T1505.004' observable: name:'Computer' type:'Hostname' - role: - 'Victim' product: - 'Splunk Enterprise' - 'Splunk Enterprise Security' - 'Splunk Cloud' required_fields: - '_time' - 'ScriptBlockText' - 'Computer' - 'EventCode' risk_score:64 security_domain:endpoint
