Windows: Renamed PAExec Execution

Rule ID

PH_Rule_SIGMA_1627

Default Status

Enabled

Description

Detects execution of renamed version of PAExec. PAExec is a remote administration tool designed as an alternative to Microsoft's PsExec. The tool is a small remote shell that includes functionality for copying files, remote execution, and fully interactive shell sessions with remote Windows machines without the need to install client software. It relies on the SMB protocol. The tool copies an executable to the hidden Admin$ share and then uses the Windows Service Control Manager API to start it as a service. The service uses named pipes, which connect back to the PAExec tool. PAExec is self-contained and doesn't use an installer. This rule is adapted from https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_renamed_paexec.yml

Severity

MITRE ATT&CK® Tactics

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/TA0005

MITRE ATT&CK® Techniques

T1202

Indirect Command Execution

Adversaries may abuse utilities that allow for command execution to bypass security restrictions that limit the use of command-line interpreters. Various Windows utilities may be used to execute commands, possibly without invoking cmd. Adversaries may abuse these features for Defense Evasion, specifically to perform arbitrary execution while subverting detections and/or mitigation controls (such as Group Policy) that limit/prevent the usage of cmd or file extensions more commonly associated with malicious payloads.

https://attack.mitre.org/techniques/T1202

Impacts

Server

Data Source

Windows Sysmon via FortiSIEM Agent

Detection

Correlation

Remediation Guidance

Investigate whether the user needs to really run PAExec or PsExec. Typically system administrators need these utilities to do their work. PAExec may be bundled with other software. In any case, running a renamed version of PAExec is unusual. If necessary, rebuild the host from a known, good source and have the user change their password.

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.

Filter

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 (description="PAExec Application" OR srcFileName="PAExec.exe" OR product REGEXP ".*PAExec.*" OR hashIMP IN ("11D40A7B7876288F919AB819CC2D9802","1a6cca4d5460b1710a12dea39e4a592c","6444f8a34e99b8f7d9647de66aabe516","dfd6aa3f7b2b1035b76b718f1ddc689f") OR hashCode REGEXP ".*IMPHASH=11D40A7B7876288F919AB819CC2D9802.*|.*IMPHASH=1a6cca4d5460b1710a12dea39e4a592c.*|.*IMPHASH=6444f8a34e99b8f7d9647de66aabe516.*|.*IMPHASH=dfd6aa3f7b2b1035b76b718f1ddc689f.*") AND (procName NOT REGEXP "\\paexec\.exe$" AND procName NOT REGEXP "^C:\\Windows\\PAExec-")

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

description,hashCode,hashIMP,hostName,procName,product,srcFileName

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

description = Filter.description,
hashCode = Filter.hashCode,
hashIMP = Filter.hashIMP,
hostName = Filter.hostName,
procName = Filter.procName,
product = Filter.product,
srcFileName = Filter.srcFileName

FortiSIEM Rules