FortiSIEM Rules

Windows: Suspicious Double Extension File Execution

Rule ID


Default Status



Detects suspicious use of an .exe extension after a non-executable file extension like .pdf.exe, a set of spaces or underlines to cloak the executable file in spear phishing campaigns. This rule is adapted from






Initial Access

Initial Access consists of techniques that use various entry vectors to gain their initial foothold within a network. Techniques used to gain a foothold include targeted spearphishing and exploiting weaknesses on public-facing web servers. Footholds gained through initial access may allow for continued access, like valid accounts and use of external remote services, or may be limited-use due to changing passwords.

MITRE ATT&CK® Techniques


Phishing: Spearphishing Attachment

Adversaries may send spearphishing emails with a malicious attachment in an attempt to elicit sensitive information and/or gain access to victim systems. Spearphishing attachment is different from other forms of spearphishing in that it employs the use of malware attached to an email. Upon opening the attachment (and potentially clicking past protections), the adversary's payload exploits a vulnerability or directly executes on the user's system. Adversaries frequently manipulate file extensions and icons in order to make attached executables appear to be document files, or files exploiting one application appear to be a file for a different one.



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-1-Create-Process" AND procName REGEXP "      \.exe$|\.doc\.exe$|\.doc\.js$|\.docx\.exe$|\.docx\.js$|\.pdf\.exe$|\.pdf\.js$|\.ppt\.exe$|\.ppt\.js$|\.pptx\.exe$|\.pptx\.js$|\.rtf\.exe$|\.rtf\.js$|\.txt\.exe$|\.txt\.js$|\.xls\.exe$|\.xls\.js$|\.xlsx\.exe$|\.xlsx\.js$|______\.exe$" AND command REGEXP ".*      \.exe.*|.*\.doc\.exe.*|.*\.doc\.js.*|.*\.docx\.exe.*|.*\.docx\.js.*|.*\.pdf\.exe.*|.*\.pdf\.js.*|.*\.ppt\.exe.*|.*\.ppt\.js.*|.*\.pptx\.exe.*|.*\.pptx\.js.*|.*\.rtf\.exe.*|.*\.rtf\.js.*|.*\.txt\.exe.*|.*\.txt\.js.*|.*\.xls\.exe.*|.*\.xls\.js.*|.*\.xlsx\.exe.*|.*\.xlsx\.js.*|.*______\.exe.*"

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

command = Filter.command,
hostName = Filter.hostName,
procName = Filter.procName