Detection rules › Elastic

Potential PowerShell Obfuscation via Special Character Overuse

Author
Elastic
Source
upstream

Detects PowerShell scripts dominated by whitespace and special characters with low symbol diversity, a profile often produced by formatting or encoding obfuscation. Attackers use symbol-heavy encoding or formatting (for example, SecureString-style blobs or character-level transforms) to hide payloads and evade static analysis and AMSI.

MITRE ATT&CK coverage

TacticTechniques
ExecutionT1059 Command and Scripting Interpreter, T1059.001 Command and Scripting Interpreter: PowerShell
Defense EvasionT1027 Obfuscated Files or Information, T1027.010 Obfuscated Files or Information: Command Obfuscation, T1140 Deobfuscate/Decode Files or Information

Event coverage

ProviderEvent IDTitle
PowerShell4104Creating Scriptblock text (MessageNumber of MessageTotal).

Stages and Predicates

Stage 1: esql:from

Stage 2: esql:where

Stage 3: esql:where

powershell.file.script_block_unique_symbols < 50

Stage 4: esql:eval

Stage 5: esql:eval

Stage 6: esql:where

Esql.script_block_length > 1000

Stage 7: esql:eval

Stage 8: esql:eval

Stage 9: esql:eval

Stage 10: esql:keep

Stage 11: esql:where

Esql.script_block_ratio >= 0.75

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.

FieldKindValues
Esql.script_block_lengthgt
  • 1000 corpus 2 (elastic 2)
Esql.script_block_ratioge
  • 0.75
powershell.file.script_block_unique_symbolslt
  • 50

Neighbors

Stricter alternatives (narrower than this rule)

The rules below may be useful if you find the current rule is too noisy / lacks specificity.