PH_Rule_SIGMA_505
Enabled
Detects suspicious launch of a renamed version of the PSEXESVC service with, which is not often used by legitimate administrators. This rule is adapted from https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_renamed_sysinternals_psexec_service.yml
7
Security
Persistence
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.
https://attack.mitre.org/tactics/TA0003No Technique Specified
Server
Windows Sysmon via FortiSIEM Agent
Correlation
Investigate whether the user needs to really run PAExec or PsExec. Typically system administrators need these utilities to do their work. Investigate why legitimate PsExec needs to be renamed. PAExec may be bundled with other software. If necessary, rebuild the host from a known, good source and have the user change their password.
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 srcFileName="psexesvc.exe" AND (procName!="C:\\Windows\\PSEXESVC.exe")
This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID
hostName,procName,srcFileName
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
hostName = Filter.hostName,
procName = Filter.procName,
srcFileName = Filter.srcFileName