Portable Gpg.EXE Execution

Status: test
Severity: medium
Log source: category process_creation, product windows
Author: frack113, Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects the execution of "gpg.exe" from uncommon location. Often used by ransomware and loaders to decrypt/encrypt data.

MITRE ATT&CK coverage

Tactic	Techniques
Impact	`T1486` Data Encrypted for Impact

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation

Rule body

title: Portable Gpg.EXE Execution
id: 77df53a5-1d78-4f32-bc5a-0e7465bd8f41
status: test
description: Detects the execution of "gpg.exe" from uncommon location. Often used by ransomware and loaders to decrypt/encrypt data.
references:
    - https://www.trendmicro.com/vinfo/vn/threat-encyclopedia/malware/ransom.bat.zarlock.a
    - https://securelist.com/locked-out/68960/
    - https://github.com/redcanaryco/atomic-red-team/blob/c4097dc7ed14d7f7d08c89d148c4307097e8c294/atomics/T1486/T1486.md
author: frack113, Nasreddine Bencherchali (Nextron Systems)
date: 2023-08-06
modified: 2023-11-10
tags:
    - attack.impact
    - attack.t1486
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        - Image|endswith:
              - '\gpg.exe'
              - '\gpg2.exe'
        - OriginalFileName: 'gpg.exe'
        - Description: 'GnuPG’s OpenPGP tool'
    filter_main_legit_location:
        Image|contains:
            - ':\Program Files (x86)\GNU\GnuPG\bin\'
            - ':\Program Files (x86)\GnuPG VS-Desktop\'
            - ':\Program Files (x86)\GnuPG\bin\'
            - ':\Program Files (x86)\Gpg4win\bin\'
    condition: selection and not 1 of filter_main_*
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    - Image|endswith:
          - '\gpg.exe'
          - '\gpg2.exe'
    - OriginalFileName: 'gpg.exe'
    - Description: 'GnuPG’s OpenPGP tool'

Stage 2: `not filter_main_legit_location`

filter_main_legit_location:
    Image|contains:
        - ':\Program Files (x86)\GNU\GnuPG\bin\'
        - ':\Program Files (x86)\GnuPG VS-Desktop\'
        - ':\Program Files (x86)\GnuPG\bin\'
        - ':\Program Files (x86)\Gpg4win\bin\'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Image`	match	`:\Program Files (x86)\GNU\GnuPG\bin\`	`excludes:Image` `field:"Image" value:":\Program Files (x86)\GNU\GnuPG\bin\"`
`Image`	match	`:\Program Files (x86)\GnuPG VS-Desktop\`	`excludes:Image` `field:"Image" value:":\Program Files (x86)\GnuPG VS-Desktop\"`
`Image`	match	`:\Program Files (x86)\GnuPG\bin\`	`excludes:Image` `field:"Image" value:":\Program Files (x86)\GnuPG\bin\"`
`Image`	match	`:\Program Files (x86)\Gpg4win\bin\`	`excludes:Image` `field:"Image" value:":\Program Files (x86)\Gpg4win\bin\"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Description`	eq	`GnuPG’s OpenPGP tool` corpus 4 (sigma 4)	`field:"Description" kind:eq value:"GnuPG’s OpenPGP tool"`
`Image`	ends_with	`\gpg.exe` corpus 4 (sigma 4) `\gpg2.exe` corpus 4 (sigma 4)	`field:"Image" kind:ends_with`
`OriginalFileName`	eq	`gpg.exe` corpus 2 (sigma 2)	`field:"OriginalFileName" kind:eq value:"gpg.exe"`