Uncoder AIの意思決定ツリーを用いたMicrosoft Defenderにおけるclfs.sys脅威活動の可視化

DeviceImageLoadEvents | where (FolderPath endswith @'clfs.sys' and ((InitiatingProcessFolderPath contains @':Perflogs' or InitiatingProcessFolderPath contains @':UsersPublic' or InitiatingProcessFolderPath contains @'Temporary Internet' or InitiatingProcessFolderPath contains @'WindowsTemp') or (InitiatingProcessFolderPath contains @':Users' and InitiatingProcessFolderPath contains @'Favorites') or (InitiatingProcessFolderPath contains @':Users' and InitiatingProcessFolderPath contains @'Favourites') or (InitiatingProcessFolderPath contains @':Users' and InitiatingProcessFolderPath contains @'Contacts') or (InitiatingProcessFolderPath contains @':Users' and InitiatingProcessFolderPath contains @'Pictures')))

1. **Initial Condition**: The query starts by looking at all `DeviceImageLoadEvents` where the `FolderPath` ends with `clfs.sys`. This means it’s specifically interested in events involving the loading of the `clfs.sys` file, which is a system file related to the Common Log File System (CLFS) used by Windows.

2. **Main Conditional Branch**:
– The query then applies an OR condition to filter these events based on the `InitiatingProcessFolderPath`. This means it checks if any of the following conditions are true for the folder path of the process that initiated the loading of `clfs.sys`.

3. **Sub-Conditions for Initiating Process Folder Path**:
– The first set of sub-conditions checks if the `InitiatingProcessFolderPath` contains specific directories that could indicate potentially malicious or unauthorized activity, such as:
– `:Perflogs`
– `:UsersPublic`
– `Temporary Internet`
– `WindowsTemp`
– These paths are often associated with temporary files, public user data, internet cache, and system temporary files, respectively. Loading system files like `clfs.sys` from these contexts could be unusual or indicative of malicious activity.

– The next set of sub-conditions checks if the `InitiatingProcessFolderPath` contains specific user directories that might indicate unauthorized access to personal data:
– `:Users` combined with any of the following: `Favorites`, `Favourites`, `Contacts`, or `Pictures`.
– These conditions aim to identify scenarios where a process, potentially malicious, is accessing sensitive user data locations while loading system files.

4. **Decision Outcome**:
– If any of these sub-conditions are met (i.e., if the `InitiatingProcessFolderPath` matches any of the specified patterns), then the event is included in the query results.
– Essentially, the query is looking for instances where the loading of `clfs.sys` might be associated with potentially suspicious or unauthorized activity based on the initiating process’s location.

In summary, this Microsoft Defender for Endpoint Query uses a detailed decision tree to identify and flag `DeviceImageLoadEvents` involving the `clfs.sys` file loaded from specific folder paths that could indicate malicious or unusual system activity.