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Detection rules › Sigma

Suspicious Calculator Usage

Status
test
Severity
high
Log source
product windows, category process_creation
Author
Florian Roth (Nextron Systems)
Source
github.com/SigmaHQ/sigma

Detects suspicious use of 'calc.exe' with command line parameters or in a suspicious directory, which is likely caused by some PoC or detection evasion.

MITRE ATT&CK coverage

TacticTechniques
StealthT1036 Masquerading

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation
Security-AuditingEvent ID 4688A new process has been created.

Rule body yaml

title: Suspicious Calculator Usage
id: 737e618a-a410-49b5-bec3-9e55ff7fbc15
status: test
description: |
    Detects suspicious use of 'calc.exe' with command line parameters or in a suspicious directory, which is likely caused by some PoC or detection evasion.
references:
    - https://twitter.com/ItsReallyNick/status/1094080242686312448
author: Florian Roth (Nextron Systems)
date: 2019-02-09
modified: 2023-11-09
tags:
    - attack.stealth
    - attack.t1036
logsource:
    category: process_creation
    product: windows
detection:
    selection_1:
        CommandLine|contains: '\calc.exe '
    selection_2:
        Image|endswith: '\calc.exe'
    filter_main_known_locations:
        Image|contains:
            - ':\Windows\System32\'
            - ':\Windows\SysWOW64\'
            - ':\Windows\WinSxS\'
    condition: selection_1 or ( selection_2 and not filter_main_known_locations )
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: condition

selection_1 or ( selection_2 and not filter_main_known_locations )

Stage 1: selection_1

selection_1:
    CommandLine|contains: '\calc.exe '

Stage 2: selection_2

selection_2:
    Image|endswith: '\calc.exe'

Stage 3: not filter_main_known_locations

filter_main_known_locations:
    Image|contains:
        - ':\Windows\System32\'
        - ':\Windows\SysWOW64\'
        - ':\Windows\WinSxS\'

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

FieldKindExcluded values
Imagematch:\Windows\SysWOW64\
Imagematch:\Windows\System32\
Imagematch:\Windows\WinSxS\

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
CommandLinematch
  • \calc.exe
Imageends_with
  • \calc.exe corpus 13 (sigma 13)