Insensitive Subfolder Search Via Findstr.EXE

Severity: low
Author: Furkan CALISKAN, @caliskanfurkan_, @oscd_initiative, Nasreddine Bencherchali (Nextron Systems)
Source: upstream

Detects execution of findstr with the "s" and "i" flags for a "subfolder" and "insensitive" search respectively. Attackers sometimes leverage this built-in utility to search the system for interesting files or filter through results of commands.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218` System Binary Proxy Execution, `T1564.004` Hide Artifacts: NTFS File Attributes
Credential Access	`T1552.001` Unsecured Credentials: Credentials In Files
Command & Control	`T1105` Ingress Tool Transfer

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `selection_findstr`

or:
CommandLine|contains: findstr
Image|endswith: findstr.exe
OriginalFileName: FINDSTR.EXE

Stage 2: `all of selection_cli_search_subfolder`

CommandLine|contains: ' -s '

Stage 3: `all of selection_cli_search_insensitive`

CommandLine|contains: ' -i '

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	`-i` corpus 3 (sigma 3) `-s` corpus 2 (sigma 2) `findstr` corpus 3 (sigma 3)
`Image`	ends_with	`findstr.exe` corpus 2 (sigma 2)
`OriginalFileName`	eq	`FINDSTR.EXE` corpus 10 (sigma 10)