GitHub Repo

Detection: Windows Suspicious Defender Update Activity in INetCache

Updated Date: 2026-04-27 ID: 3e25f906-6319-44ad-ab9a-22d162eb3925 Author: Raven Tait, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

Detects a non-Defender process writing mpam-fe*.exe to the Windows Internet Cache (INetCache). BlueHammer downloads the WD signature update package directly using WinINet as a low-privileged user. The [1].exe naming suffix is produced by Windows HTTP caching and is a reliable artifact of this download method.

 1`sysmon`
 2EventID IN ("11","23")
 3TargetFilename="*\\INetCache*"
 4TargetFilename="*\\mpam-fe[1].exe*"
 5NOT Image IN (
 6    "*:\\Program Files\\Windows Defender*",
 7    "*:\\ProgramData\\Microsoft\\Windows Defender*",
 8    "*:\\Windows\\System32\\MpSigStub.exe*"
 9)
10
11| fillnull
12
13| rename Computer as dest
14
15| stats count by dest TargetFilename Image EventID
16                 action file_name file_path process_guid
17                 process_id user vendor_product
18
19| `security_content_ctime(firstTime)`
20
21| `security_content_ctime(lastTime)`
22
23| `windows_suspicious_defender_update_activity_in_inetcache_filter`

Data Source

Name Platform Sourcetype Source
Sysmon EventID 23 Windows icon Windows 'XmlWinEventLog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
Sysmon EventID 11 Windows icon Windows 'XmlWinEventLog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'

Macros Used

Name Value
sysmon (source=WinEventLog:Microsoft-Windows-Sysmon/Operational OR source=XmlWinEventLog:Microsoft-Windows-Sysmon/Operational OR source=Syslog:Linux-Sysmon/Operational)
windows_suspicious_defender_update_activity_in_inetcache_filter search *
windows_suspicious_defender_update_activity_in_inetcache_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1068 Exploitation for Privilege Escalation Privilege Escalation
T1105 Ingress Tool Transfer Command and Control
Exploitation
Command and Control
DE.AE
CIS 10

CVE

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Finding (Notable) No
Creates Intermediate Finding (Risk Event) Yes
Anomaly detections generate Intermediate Findings (Risk Events). They do not generate a Finding (Notable) directly.

Implementation

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Processes node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

Some legitimate system maintenance tools or security scanners may download updates using WinINet and write to INetCache with similar naming patterns. Filter alerts when these tools are verified and approved.

Associated Analytic Story

Intermediate Findings

Message Entity Field Entity Type Risk Score
Defender Update package $file_path$ downloaded to INetCache by unexpected process $Image$ on $dest$. dest system 20

Threat Objects

Field Type
Image process

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational XmlWinEventLog
Integration ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational XmlWinEventLog

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 1