FortiSIEM Rules

Windows: Suspicious Volume Shadow Copy VSS-PS.dll Load

Rule ID


Default Status



Detects the image load of vss_ps.dll by uncommon executables. This rule is adapted from







Impact consists of techniques that adversaries use to disrupt availability or compromise integrity by manipulating business and operational processes. Techniques used for impact can include destroying or tampering with data. In some cases, business processes can look fine, but may have been altered to benefit the adversaries’ goals. These techniques might be used by adversaries to follow through on their end goal or to provide cover for a confidentiality breach.

MITRE ATT&CK® Techniques


Inhibit System Recovery

Adversaries may delete or remove built-in operating system data and turn off services designed to aid in the recovery of a corrupted system to prevent recovery. Operating systems may contain features that can help fix corrupted systems, such as a backup catalog, volume shadow copies, and automatic repair features. Adversaries may disable or delete these system recovery features.



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-7-Image-Loaded" AND loadedProcName REGEXP "\\vss_ps\.dll$" AND ((procName NOT REGEXP "^C:\\Windows\\" OR procName NOT REGEXP "\\System32\\SystemPropertiesAdvanced\.exe$|\\WmiPrvSE\.exe$|\\clussvc\.exe$|\\dismhost\.exe$|\\dllhost\.exe$|\\inetsrv\\appcmd\.exe$|\\inetsrv\\iissetup\.exe$|\\msiexec\.exe$|\\rundll32\.exe$|\\searchindexer\.exe$|\\srtasks\.exe$|\\svchost\.exe$|\\taskhostw\.exe$|\\thor64\.exe$|\\thor\.exe$|\\tiworker\.exe$|\\vssvc\.exe$") AND (procName NOT REGEXP "^C:\\Program Files \(x86\)\\|^C:\\Program Files\\") AND (command NOT REGEXP "^C:\\\$WinREAgent\\Scratch\\" OR command NOT REGEXP ".*\\dismhost\.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,
loadedProcName = Filter.loadedProcName,
procName = Filter.procName