Suspicious AgentExecutor PowerShell Execution

Severity: high
Author: Nasreddine Bencherchali (Nextron Systems), memory-shards
Source: upstream

Detects execution of the AgentExecutor.exe binary. Which can be abused as a LOLBIN to execute powershell scripts with the ExecutionPolicy "Bypass" or any binary named "powershell.exe" located in the path provided by 6th positional argument

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218` System Binary Proxy Execution

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\AgentExecutor.exe'
OriginalFileName: AgentExecutor.exe

Stage 2: `all of selection_cli`

or:
CommandLine|contains: ' -powershell'
CommandLine|contains: ' -remediationScript'

Stage 3: `not 1 of filter_main_*`

or:
CommandLine|contains: 'C:\Windows\SysWOW64\WindowsPowerShell\v1.0\'
CommandLine|contains: 'C:\Windows\System32\WindowsPowerShell\v1.0\'
ParentImage|endswith: '\Microsoft.Management.Services.IntuneWindowsAgent.exe'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`CommandLine`	match	`-powershell` corpus 2 (sigma 2) `-remediationScript` corpus 2 (sigma 2) `C:\Windows\SysWOW64\WindowsPowerShell\v1.0\` `C:\Windows\System32\WindowsPowerShell\v1.0\`
`Image`	ends_with	`\AgentExecutor.exe`
`OriginalFileName`	eq	`AgentExecutor.exe` corpus 2 (sigma 2)
`ParentImage`	ends_with	`\Microsoft.Management.Services.IntuneWindowsAgent.exe` corpus 2 (sigma 2)