Suspicious PowerShell Encoded Command Patterns

Severity: high
Author: Florian Roth (Nextron Systems)
Source: upstream

Detects PowerShell command line patterns in combincation with encoded commands that often appear in malware infection chains

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\powershell.exe'
Image|endswith: '\pwsh.exe'
OriginalFileName: PowerShell.Exe
OriginalFileName: pwsh.dll

Stage 2: `all of selection_flags`

or:
CommandLine|contains: ' -e '
CommandLine|contains: ' -en '
CommandLine|contains: ' -enc '
CommandLine|contains: ' -enco'

Stage 3: `all of selection_encoded`

or:
CommandLine|contains: ' IAB'
CommandLine|contains: ' JAB'
CommandLine|contains: ' PAA'
CommandLine|contains: ' SQBFAFgA'
CommandLine|contains: ' SUVYI'
CommandLine|contains: ' aQBlAHgA'
CommandLine|contains: ' aWV4I'

Stage 4: `not 1 of filter_gcworker`

or:
ParentImage|contains: 'C:\Packages\Plugins\Microsoft.GuestConfiguration.ConfigurationforWindows\'
ParentImage|contains: '\gc_worker.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	`-e` corpus 5 (sigma 5) `-en` corpus 3 (sigma 3) `-enc` corpus 6 (sigma 6) `-enco` corpus 2 (sigma 2) `IAB` corpus 2 (sigma 2) `JAB` corpus 2 (sigma 2) `PAA` `SQBFAFgA` corpus 2 (sigma 2) `SUVYI` corpus 2 (sigma 2) `aQBlAHgA` corpus 2 (sigma 2) `aWV4I` corpus 2 (sigma 2)
`Image`	ends_with	`\powershell.exe` corpus 143 (sigma 143) `\pwsh.exe` corpus 140 (sigma 140)
`OriginalFileName`	eq	`PowerShell.Exe` corpus 2 (sigma 2) `pwsh.dll` corpus 72 (sigma 68, splunk 4)
`ParentImage`	match	`C:\Packages\Plugins\Microsoft.GuestConfiguration.ConfigurationforWindows\` corpus 2 (sigma 2) `\gc_worker.exe` corpus 2 (sigma 2)

Suspicious PowerShell Encoded Command Patterns

MITRE ATT&CK coverage

Event coverage

Stages and Predicates

Stage 1: all of selection_img

Stage 2: all of selection_flags

Stage 3: all of selection_encoded

Stage 4: not 1 of filter_gcworker

Indicators

Stage 1: `all of selection_img`

Stage 2: `all of selection_flags`

Stage 3: `all of selection_encoded`

Stage 4: `not 1 of filter_gcworker`