File Encryption/Decryption Via Gpg4win From Suspicious Locations

Severity: high
Author: Nasreddine Bencherchali (Nextron Systems), X__Junior (Nextron Systems)
Source: upstream

Detects usage of Gpg4win to encrypt/decrypt files located in potentially suspicious locations.

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_metadata`

or:
Description: 'GnuPG’s OpenPGP tool'
Image|endswith: '\gpg.exe'
Image|endswith: '\gpg2.exe'
Product: 'GNU Privacy Guard (GnuPG)'

Stage 2: `all of selection_cli`

CommandLine|contains: -passphrase

Stage 3: `all of selection_paths`

or:
CommandLine|contains: ':\PerfLogs\'
CommandLine|contains: ':\Temp\'
CommandLine|contains: ':\Users\Public\'
CommandLine|contains: ':\Windows\Temp\'
CommandLine|contains: '\AppData\Local\Temp\'
CommandLine|contains: '\AppData\Roaming\'

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	`-passphrase` `:\PerfLogs\` corpus 6 (sigma 6) `:\Temp\` corpus 14 (sigma 14) `:\Users\Public\` corpus 14 (sigma 14) `:\Windows\Temp\` corpus 15 (sigma 15) `\AppData\Local\Temp\` corpus 16 (sigma 16) `\AppData\Roaming\` corpus 10 (sigma 10)
`Description`	eq	`GnuPG’s OpenPGP tool` corpus 4 (sigma 4)
`Image`	ends_with	`\gpg.exe` corpus 5 (sigma 5) `\gpg2.exe` corpus 5 (sigma 5)
`Product`	eq	`GNU Privacy Guard (GnuPG)`