Detection: Windows RDP Bitmap Cache File Creation

Updated Date: 2025-07-30 ID: 5f8671b6-07a7-425d-b3da-c39a53f2a6ae Author: Teoderick Contreras, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

This detection identifies the creation of Remote Desktop Protocol (RDP) bitmap cache files on a Windows system, typically located in the user’s profile under the Terminal Server Client cache directory. These files (.bmc, cache.bin) are generated when a user initiates an RDP session using the built-in mstsc.exe client. Their presence can indicate interactive remote access activity and may be useful in detecting lateral movement or unauthorized RDP usage. Monitoring this behavior is especially important, as attackers may attempt to delete or suppress these artifacts to evade forensic analysis.

Search

1
2| tstats `security_content_summariesonly` count  min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.file_path IN ("*\\Terminal Server Client\\Cache\\*.bmc", "*\\Terminal Server Client\\Cache\\cache*.bin") by Filesystem.action Filesystem.dest Filesystem.file_access_time Filesystem.file_create_time Filesystem.file_hash Filesystem.file_modify_time Filesystem.file_name Filesystem.file_path Filesystem.file_acl Filesystem.file_size Filesystem.process_guid Filesystem.process_id Filesystem.user Filesystem.vendor_product 
3| `security_content_ctime(lastTime)` 
4| `security_content_ctime(firstTime)` 
5|`drop_dm_object_name(Filesystem)` 
6| `windows_rdp_bitmap_cache_file_creation_filter`

Data Source

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

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
windows_rdp_bitmap_cache_file_creation_filter	`search *`

windows_rdp_bitmap_cache_file_creation_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
T1021.001	Remote Desktop Protocol	Lateral Movement

Exploitation

DE.AE

CIS 10

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 Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

To successfully implement this search, you must ingest logs that include the process name, TargetFilename, and ProcessID executions from your endpoints. If you are utilizing Sysmon, ensure you have at least version 2.0 of the Sysmon TA installed.

Known False Positives

False positives will be present, filter as needed or restrict to critical assets on the perimeter.

Associated Analytic Story

Windows RDP Artifacts and Defense Evasion

Risk Based Analytics (RBA)

Risk Message:

A rdp bitmap cache has been identified on $dest$.

Risk Object	Risk Object Type	Risk Score	Threat Objects
dest	system	20	No Threat Objects

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