Windows Unusual Process Load Mozilla NSS-Mozglue Module

Name:Windows Unusual Process Load Mozilla NSS-Mozglue Module
id:1a7e7650-b81d-492e-99d4-d5ab633afbdd
version:1
date:2025-07-16
author:Teoderick Contreras, Splunk
status:production
type:Anomaly
Description:The following analytic identifies processes loading Mozilla NSS-Mozglue libraries such as mozglue.dll and nss3.dll. It leverages Sysmon Event logs, specifically monitoring EventCode 7, which tracks image loaded events. This activity is significant because it can indicate unauthorized access or manipulation of these libraries, which are commonly used by Mozilla applications like Firefox and Thunderbird. If confirmed malicious, this could lead to data exfiltration, credential theft, or further compromise of the system.
Data_source:

• -Sysmon EventID 7

search:`sysmon` EventCode=7 ImageLoaded IN ("*\\mozglue.dll", "*\\nss3.dll") NOT(process_path IN("*:\\Program Files\Mozilla Firefox\\firefox.exe", "*:\\Program Files (x86)\Mozilla Firefox\\firefox.exe", "*:\\Program Files\\Mozilla Thunderbird\\thunderbird.exe", "*:\\Program Files (x86)\\Mozilla Thunderbird\\thunderbird.exe", "*\\Tor Browser\\Browser\\firefox.exe","*:\\Program Files\\Code42\\CrashPlan\\Code42Service.exe", "*:\\Program Files (x86)\\Code42\\CrashPlan\\Code42Service.exe", "*:\\Program Files\\Pale Moon\\palemoon.exe", "*:\\Program Files (x86)\\Pale Moon\\palemoon.exe", "*:\\Program Files\\Waterfox\\waterfox.exe","*:\\Program Files (x86)\\Waterfox\\waterfox.exe", "*:\\Program Files\\Cyberfox\cyberfox.exe", "*:\\Program Files (x86)\\Cyberfox\\cyberfox.exe", "*\\AppData\\Local\\slack\\slack.exe", "*:\\Program Files (x86)\\VMware\\VMware Horizon View Client\\vmware-view.exe", "*:\\Program Files (x86)\\Dropbox\\Client\\Dropbox.exe", "*:\\Program Files\\Google\\Google Earth Pro\\client\\googleearth.exe"))
| 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_unusual_process_load_mozilla_nss_mozglue_module_filter`

how_to_implement:To successfully implement this search, you need to be ingesting logs with the process name and imageloaded executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.
known_false_positives:Legitimate windows application that are not on the list loading this dll. Filter as needed.
References:
  -https://www.trendmicro.com/vinfo/nz/threat-encyclopedia/malware/trojanspy.win32.vidar.yxdftz
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 ("$dest$") 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:
    - 'Quasar RAT'
  asset_type:Endpoint
  mitre_attack_id:
    - 'T1218.003'
  product:
    - 'Splunk Enterprise'
    - 'Splunk Enterprise Security'
    - 'Splunk Cloud'
  security_domain:endpoint

tests:
 name:'True Positive Test'
 attack_data:
  data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1218.003/moz_lib_loaded/mozilla_lib.log
  source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
  sourcetype: XmlWinEventLog
manual_test:None