ID | Technique | Tactic |
---|---|---|
T1564 | Hide Artifacts | Defense Evasion |
T1564.004 | NTFS File Attributes | Defense Evasion |
Detection: Windows Alternate DataStream - Base64 Content
Description
The following analytic detects the creation of Alternate Data Streams (ADS) with Base64 content on Windows systems. It leverages Sysmon EventID 15, which captures file creation events, including the content of named streams. ADS can conceal malicious payloads, making them significant for SOC monitoring. This detection identifies hidden streams that may contain executables, scripts, or configuration data, often used by malware to evade detection. If confirmed malicious, this activity could allow attackers to hide and execute payloads, persist in the environment, or access sensitive information without being easily detected.
Search
1`sysmon` EventCode=15 NOT Contents IN ("-","[ZoneTransfer]*")
2| regex TargetFilename="(?<!\/)\b\w+(\.\w+)?:\w+(\.\w+)?$"
3| regex Contents="(?:[A-Za-z0-9+/]{128,})(?:[A-Za-z0-9+/]{2}==
4|[A-Za-z0-9+/]{3}=)?$"
5| eval file_name = replace(TargetFilename,"(.*\\\)",""), process = Image , file_path = TargetFilename , base64 = Contents, file_hash = coalesce(SHA256,SHA1,MD5,Hash)
6| stats count min(_time) as firstTime max(_time) as lastTime values(user) as user by dest, process, process_guid, file_name, file_path, file_hash, base64
7| `base64decode(base64)`
8| fields - base64
9| rename base64_decode as command
10| `security_content_ctime(firstTime)`
11| `security_content_ctime(lastTime)`
12| `windows_alternate_datastream___base64_content_filter`
Data Source
Name | Platform | Sourcetype | Source | Supported App |
---|---|---|---|---|
Sysmon EventID 15 | Windows | 'xmlwineventlog' |
'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational' |
N/A |
Macros Used
Name | Value |
---|---|
base64decode | `eval b64x_split=split($b64in$,"") |
windows_alternate_datastream___base64_content_filter | search * |
windows_alternate_datastream___base64_content_filter
is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Annotations
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 Notable | Yes |
Rule Title | %name% |
Rule Description | %description% |
Notable Event Fields | user, dest |
Creates Risk Event | True |
Implementation
Target environment must ingest sysmon data, specifically Event ID 15.
Known False Positives
Unknown
Associated Analytic Story
Risk Based Analytics (RBA)
Risk Message | Risk Score | Impact | Confidence |
---|---|---|---|
Base64 content written to an NTFS alternate data stream by $user$, see command field for details. | 80 | 100 | 80 |
References
-
https://gist.github.com/api0cradle/cdd2d0d0ec9abb686f0e89306e277b8f
-
https://github.com/trustedsec/SysmonCommunityGuide/blob/master/chapters/file-stream-creation-hash.md
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: 3