Filefinder

Overview

Spyware:Win32/Filefinder is a specialized information-stealing trojan designed explicitly for data exfiltration and reconnaissance. Unlike broad stealers that grab browser passwords, Filefinder acts more like a targeted search engine for the attacker, silently scanning the compromised file system and network shares for specific documents, databases, or intellectual property, and uploading them to a remote server.

Understanding Filefinder (Spyware/Data Stealers)
To an end-user, Filefinder is invisible; it does not display ransom notes or degrade performance significantly. For an enterprise, it represents a critical data breach. Attackers deploy Filefinder after gaining initial access to map the network and extract high-value data (like `.docx`, `.pdf`, `.sql`, `.key`, or custom proprietary extensions) before deploying a louder payload like ransomware.

Execution and Data Exfiltration Mechanics
Filefinder is typically deployed manually by an attacker who has already achieved interactive access (e.g., via RDP or a backdoor). It is designed to run quietly in the background. It utilizes native Windows APIs (like `FindFirstFile` and `FindNextFile`) (`T1083`) to aggressively traverse local drives and mapped SMB shares (`T1039`). It is often configured with a specific list of target file extensions or keywords. When matching files are found, it copies them to a hidden staging directory (`T1074.001`), often compressing and encrypting them into a single archive (like a password-protected `.zip` or `.rar`) (`T1560.001`). Finally, it exfiltrates the archive to the attacker's C2 server using FTP, HTTP POST requests, or cloud storage APIs (`T1048.003`).

Indicators of Compromise & Impact
The impact is a severe breach of confidentiality and intellectual property theft. Host-based IoCs include EDR alerts for anomalous, high-volume file read operations by an unknown executable, the creation of large, encrypted archive files in temporary directories (staging), and unexpected scheduled tasks used for persistence. Network IoCs involve large outbound data transfers to unknown IP addresses or unrecognized cloud storage providers.

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to the MITRE ATT&CK framework:

Generated Detections (Boilerplate)

These YARA and Sigma rules are auto-generated based on the family name and aliases. They must be heavily tuned before deployment in a production environment.

YARA Rule

rule MALWARE_WIN_FILEFINDER {
    meta:
        description = "Detects Filefinder (ransomware)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "filefinder" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Filefinder Activity
id: 42d99e6763285b10d79cebdc73e05a3a
status: experimental
description: Detects generic indicators of the filefinder malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*filefinder*"
    condition: selection
level: medium

Containment & Response Steps

Ordered checklist for responders. Adapt to your environment and engage professional support for active incidents.

1. Isolate the endpoint immediately to halt any ongoing data exfiltration.
2. Analyze the memory or the configuration file of the Filefinder executable to determine exactly which file types and directories were targeted.
3. Review network egress logs to quantify the amount of data exfiltrated and identify the destination IP addresses/domains.
4. Initiate incident response protocols for a confirmed data breach, as sensitive intellectual property or PII has likely been compromised.

What to Avoid

Common mistakes during response to this family that can destroy evidence, spread the infection, or worsen recovery.

1. Do not simply delete the malware and assume the incident is over; the primary damage (data theft) has likely already occurred, requiring a full breach investigation.
2. Avoid rebooting the machine, as evidence of the staging directory or the active exfiltration connection may be lost.

References & External Analysis

• Search "filefinder" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: ransomware)

Explore other malware families in the same category:

• Genericrxfo
• Genx
• Zilix
• Winload
• Inservice

Machine-readable

Get this profile as JSON: https://jordanricky1604-ship-it.github.io/malware-families-catalog/api/filefinder.json

Ecosystem & Interactive Environments

This profile is part of the Malware Families Catalog, a public dataset of 2,899 malware families. The catalog is also published across our ecosystem: Hugging Face, Kaggle, Zenodo, Replit, StackBlitz, CodeSandbox, and CodePen.