Potential PowerShell Obfuscation Via Reversed Commands

Severity: high
Author: Teymur Kheirkhabarov (idea), Vasiliy Burov (rule), oscd.community, Tim Shelton
Source: upstream

Detects the presence of reversed PowerShell commands in the CommandLine. This is often used as a method of obfuscation by attackers

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell
Defense Evasion	`T1027` Obfuscated Files or Information

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_cli`

or:
CommandLine|contains: 46esab
CommandLine|contains: daolnwod
CommandLine|contains: dnammoc
CommandLine|contains: eddih
CommandLine|contains: ekovn
CommandLine|contains: eliFd
CommandLine|contains: elifotevas
CommandLine|contains: esnopser
CommandLine|contains: etirw
CommandLine|contains: golon
CommandLine|contains: hcaerof
CommandLine|contains: hctac
CommandLine|contains: htaPpmeTteG
CommandLine|contains: kaerb
CommandLine|contains: llehsrewop
CommandLine|contains: maerts
CommandLine|contains: ptth
CommandLine|contains: rahc
CommandLine|contains: retupmoc
CommandLine|contains: ssecorp
CommandLine|contains: tcejbO
CommandLine|contains: tneilCbeW
CommandLine|contains: tneilc
CommandLine|contains: tninon
CommandLine|contains: tpircS

Stage 3: `not 1 of filter_main_encoded_keyword`

or:
CommandLine|contains: ' -EncodedCommand '
CommandLine|contains: ' -enc '

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	`-EncodedCommand` corpus 2 (sigma 2) `-enc` corpus 6 (sigma 6) `46esab` `daolnwod` `dnammoc` `eddih` `ekovn` `eliFd` `elifotevas` `esnopser` `etirw` `golon` `hcaerof` `hctac` `htaPpmeTteG` `kaerb` `llehsrewop` `maerts` `ptth` `rahc` `retupmoc` `ssecorp` `tcejbO` `tneilCbeW` `tneilc` `tninon` `tpircS`
`Image`	ends_with	`\powershell.exe` corpus 143 (sigma 143) `\pwsh.exe` corpus 140 (sigma 140)
`OriginalFileName`	eq	`PowerShell.EXE` corpus 64 (sigma 60, splunk 4) `pwsh.dll` corpus 72 (sigma 68, splunk 4)