PH_Rule_SIGMA_635
Enabled
Extensible Stylesheet Language (XSL) files are commonly used to describe the processing and rendering of data within XML files. Rule detects when adversaries abuse this functionality to execute arbitrary files while potentially bypassing application whitelisting defenses. This rule is adapted from https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_wmic_xsl_script_processing.yml
5
Security
Defense Evasion
Defense Evasion consists of techniques that adversaries use to avoid detection throughout their compromise. Techniques used for defense evasion include uninstalling/disabling security software or obfuscating/encrypting data and scripts. Adversaries also leverage and abuse trusted processes to hide and masquerade their malware. Other tactics’ techniques are cross-listed here when those techniques include the added benefit of subverting defenses.
https://attack.mitre.org/tactics/TA0005T1220
XSL Script Processing
Adversaries may bypass application control and obscure execution of code by embedding scripts inside XSL files. Extensible Stylesheet Language (XSL) files are commonly used to describe the processing and rendering of data within XML files. To support complex operations, the XSL standard includes support for embedded scripting in various languages. Adversaries may abuse this functionality to execute arbitrary files while potentially bypassing application control.
https://attack.mitre.org/techniques/T1220Server
Windows Sysmon via FortiSIEM Agent
Correlation
No remediation guidance specified
If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.
300 seconds
If the following defined pattern/s occur within a 300 second time window.
Filter
This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.
This is the query logic that matches incoming events
eventType="Win-Sysmon-1-Create-Process" AND (((procName REGEXP "\\wmic\.exe$" AND command REGEXP ".*-format.*|.*/format.*") AND (command NOT REGEXP ".*Format:List.*|.*Format:csv.*|.*Format:hform.*|.*Format:htable.*|.*Format:mof.*|.*Format:rawxml.*|.*Format:table.*|.*Format:value.*|.*Format:xml.*")) OR procName REGEXP "\\msxsl\.exe$")
This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID
command,hostName,procName
This is most typically a numerical constraint that defines when the rule should trigger an incident
COUNT(*) >= 1
This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.
The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern
command = Filter.command,
hostName = Filter.hostName,
procName = Filter.procName