FortiSIEM Rules

Windows: Potential Persistence Via Microsoft Office Add-In

Rule ID


Default Status



Detects potential persistence activity via startup add-ins that load when Microsoft Office starts (.wll/.xll are simply .dll fit for Word or Excel). This rule is adapted from







Persistence consists of techniques that adversaries use to keep access to systems across restarts, changed credentials, and other interruptions that could cut off their access. Techniques used for persistence include any access, action, or configuration changes that let them maintain their foothold on systems, such as replacing or hijacking legitimate code or adding startup code.

MITRE ATT&CK® Techniques


Office Application Startup: Add-ins

Adversaries may abuse Microsoft Office add-ins to obtain persistence on a compromised system. Office add-ins can be used to add functionality to Office programs. There are different types of add-ins that can be used by the various Office products; including Word/Excel add-in Libraries (WLL/XLL), VBA add-ins, Office Component Object Model (COM) add-ins, automation add-ins, VBA Editor (VBE), Visual Studio Tools for Office (VSTO) add-ins, and Outlook add-ins. Add-ins can be used to obtain persistence because they can be set to execute code when an Office application starts.



Data Source

Windows Sysmon via FortiSIEM Agent



Remediation Guidance

No remediation guidance specified

Time Window

If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.

300 seconds

Trigger Conditions

If the following defined pattern/s occur within a 300 second time window.


SubPattern Definitions

SubPattern Name: Filter

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

eventType="Win-Sysmon-11-FileCreate" AND ((fileName REGEXP ".*\\Microsoft\\Word\\Startup\\.*" AND fileName REGEXP "\.wll$") OR (fileName REGEXP ".*\\Microsoft\\Excel\\Startup\\.*" AND fileName REGEXP "\.xll$") OR (fileName REGEXP ".*Microsoft\\Excel\\XLSTART\\.*" AND fileName REGEXP "\.xlam$") OR (fileName REGEXP ".*\\Microsoft\\Addins\\.*" AND fileName REGEXP "\.ppam$|\.xla$|\.xlam$"))

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID


Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

COUNT(*) >= 1

Incident Attribute Mapping

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

fileName = Filter.fileName,
hostName = Filter.hostName