Windows Unsigned MS DLL Side-Loading

SPLUNK detection rule by Teoderick Contreras, Splunk · Apache-2.0

The following analytic identifies potential DLL side-loading instances involving unsigned DLLs mimicking Microsoft signatures. It detects this activity by analyzing Sysmon logs for Event Code 7, where both the `Image` and `ImageLoaded` paths do not match system directories like `system32`, `syswow64`, and `programfiles`. This behavior is significant as adversaries often exploit DLL side-loading to execute malicious code via legitimate processes. If confirmed malicious, this activity could allow attackers to execute arbitrary code, potentially leading to privilege escalation, persistence, and unauthorized access to sensitive information.

name: Windows Unsigned MS DLL Side-Loading
id: 8d9e0e06-ba71-4dc5-be16-c1a46d58728c
version: 16
creation_date: '2024-04-17'
modification_date: '2026-05-13'
author: Teoderick Contreras, Splunk
status: production
type: Anomaly
description: The following analytic identifies potential DLL side-loading instances involving unsigned DLLs mimicking Microsoft signatures. It detects this activity by analyzing Sysmon logs for Event Code 7, where both the `Image` and `ImageLoaded` paths do not match system directories like `system32`, `syswow64`, and `programfiles`. This behavior is significant as adversaries often exploit DLL side-loading to execute malicious code via legitimate processes. If confirmed malicious, this activity could allow attackers to execute arbitrary code, potentially leading to privilege escalation, persistence, and unauthorized access to sensitive information.
data_source:
    - Sysmon EventID 7
search: |
    `sysmon`
    EventCode=7
    Company="Microsoft Corporation"
    Signed=false
    SignatureStatus!= Valid
    NOT (Image IN (
                  "C:\\Program Files \(x86\)\\*",
                  "C:\\Program Files\\*",
                  "C:\\Windows\\System32\\*",
                  "C:\\Windows\\SysWow64\\*"
                  )
        )
    NOT (ImageLoaded IN (
                        "C:\\Program Files \(x86\)\\*",
                        "C:\\Program Files\\*",
                        "C:\\Windows\\System32\\*",
                        "C:\\Windows\\SysWow64\\*"
                        )
        )
    | rex field=Image "(?<ImageFolderPath>.+\\\)"
    | rex field=ImageLoaded "(?<ImageLoadedFolderPath>.+\\\)"
    | where ImageFolderPath = ImageLoadedFolderPath
    | 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_unsigned_ms_dll_side_loading_filter`
how_to_implement: The analytic is designed to be run against Sysmon event logs collected from endpoints. The analytic requires the Sysmon event logs to be ingested into Splunk. The analytic searches for EventCode 7 where the Image is either SQLDumper.exe or SQLWriter.exe and the ImageLoaded is vcruntime140.dll. The search also filters out the legitimate loading of vcruntime140.dll from the System32 directory to reduce false positives. The analytic can be modified to include additional known good paths for vcruntime140.dll to further reduce false positives.
known_false_positives: False positives are possible if legitimate processes are loading vcruntime140.dll from non-standard directories. It is recommended to investigate the context of the process loading vcruntime140.dll to determine if it is malicious or not. Modify the search to include additional known good paths for vcruntime140.dll to reduce false positives.
references:
    - https://www.mandiant.com/resources/blog/apt29-wineloader-german-political-parties
    - https://www.zscaler.com/blogs/security-research/european-diplomats-targeted-spikedwine-wineloader
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"
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: An instance of $Image$ loading Unsigned $ImageLoaded$ was detected on $dest$.
threat_objects:
    - field: Image
      type: file_name
analytic_story:
    - China-Nexus Threat Activity
    - Derusbi
    - APT29 Diplomatic Deceptions with WINELOADER
    - Salt Typhoon
    - Earth Alux
    - XWorm
threat_group:
    - APT29
    - Cozy Bear
    - Midnight Blizzard
asset_type: Endpoint
mitre_attack_id:
    - T1574.001
    - T1547
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/T1574.002/unsigned_dll_load/wineloader_dll_sideload.log
          sourcetype: XmlWinEventLog
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
      test_type: unit

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4646d4c0-c465-4d43-9798-58366805af2e

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