Detection rules › Sigma

Use of FSharp Interpreters

Severity
medium
Author
Christopher Peacock @SecurePeacock, SCYTHE @scythe_io
Source
upstream

Detects the execution of FSharp Interpreters "FsiAnyCpu.exe" and "FSi.exe" Both can be used for AWL bypass and to execute F# code via scripts or inline.

MITRE ATT&CK coverage

TacticTechniques
ExecutionT1059 Command and Scripting Interpreter

Event coverage

ProviderEvent IDTitle
Sysmon1Process creation

Stages and Predicates

Stage 1: selection

or:
Image|endswith: '\fsi.exe'
Image|endswith: '\fsianycpu.exe'
OriginalFileName: fsi.exe
OriginalFileName: fsianycpu.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.

FieldKindValues
Imageends_with
  • \fsi.exe
  • \fsianycpu.exe
OriginalFileNameeq
  • fsi.exe
  • fsianycpu.exe