Frethog

Overview

Executive Summary

Infection Vector and Technical Capabilities

• Targeted Credential Extraction: Frethog actively searches for and parses the local credential databases of major web browsers (Chrome, Firefox, Internet Explorer). It is also notoriously known for specifically targeting the configuration files of popular online games (like World of Warcraft or Steam) and FTP clients to steal session tokens and passwords.
• Keylogging Capabilities: Some variants incorporate API hooking (e.g., `SetWindowsHookEx`) to record keystrokes, ensuring they capture passwords even if they are not permanently saved in the browser or application.
• Data Exfiltration: The harvested credentials, along with basic system reconnaissance data, are compressed and rapidly exfiltrated to the attacker's Command and Control (C2) server, usually via HTTP POST requests or sometimes via automated email (SMTP).

Threat Assessment

Incident Response and Remediation

• Immediate Endpoint Isolation: The highest priority is to disconnect the infected endpoint from the network to halt the active exfiltration of the stolen credentials.
• Global Credential and Session Reset: It must be assumed that all passwords and session tokens present on the machine have been stolen. A mandatory, immediate reset of all associated enterprise passwords is required. The user must be advised to reset all personal accounts as well.
• Complete Re-imaging: To ensure no hidden persistence mechanisms or secondary backdoors remain, the compromised endpoint must undergo a complete bare-metal wipe and re-image from a trusted baseline.

Known aliases

Threat reports may refer to this family under multiple names:

• PWS:Win32/Frethog
• Trojan.PWS.Frethog
• Infostealer.Frethog

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:

Tactical Mitigations

Based on the techniques used by this family, consider the following defensive strategies:

• T1056.001: Implement Endpoint Detection and Response (EDR) to monitor for suspicious API calls related to keystroke interception. Enforce Multi-Factor Authentication (MFA) to render stolen passwords useless.

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

Tiered Detection Rules (Cisco CAIRN Model)

Modern threat detection requires multi-layered rule engineering. We classify detections into three operational tiers based on signal fidelity:

rule MALWARE_WIN_FRETHOG_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Frethog"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "frethog" ascii wide nocase
        $s2 = "pws:win32/frethog" ascii wide nocase
        $s3 = "trojan.pws.frethog" ascii wide nocase
        $s4 = "infostealer.frethog" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Frethog (Trojan) Execution & Triage
id: 6aa5d5f8-34fd-59ea-87e7-84ec5272369b
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Frethog malware family. Detects suspicious execution from temporary user
  directories with hidden window flags and background transfer utilities.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/frethog
- https://malware-families-catalog.systemhelpdesk.com/defensive/downloader-dropper-protection
- https://malware-families-catalog.systemhelpdesk.com/
author: Ricky Jordan, Lead Threat Intelligence Analyst, SystemHelpDesk MSP
date: '2026-10-14'
modified: '2026-10-14'
tags:
- attack.trojan
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1555_003
- attack.t1056_001
- attack.t1005
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \cmd.exe
    - \powershell.exe
    - \cscript.exe
    - \wscript.exe
    CommandLine|contains:
    - AppData\Local\Temp
    - -WindowStyle Hidden
    - /e:jscript
    - bitsadmin /transfer
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: medium

rule MALWARE_WIN_FRETHOG_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Frethog tradecraft"
        tier = "T3 - Attribution Fingerprint"
        confidence = "High (Confirmed Family Signature)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        // Core family identifier & heuristic payload signatures
        $attrib_str = "frethog" ascii wide nocase
        $pe_magic = "MZ" ascii
        $net_marker = "http" ascii nocase
    condition:
        uint16(0) == 0x5a4d and ($attrib_str and $net_marker) and filesize < 15MB
}

Containment & Response Steps

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

1. Sever network connectivity for the flagged endpoint to terminate persistent command-and-control (C2) communication channels and stop Frethog from retrieving secondary stage payloads.
2. Capture process memory triage to detect and terminate malicious threads injected by Frethog into legitimate system processes such as explorer.exe or svchost.exe.
3. Audit Windows Registry Run keys (HKCU\Software\Microsoft\Windows\CurrentVersion\Run) and Task Scheduler entries to locate and purge Frethog persistence hooks.
4. Deploy updated enterprise EDR detection signatures and conduct an out-of-band endpoint scan to isolate dropped binaries and staged payloads.
5. Rotate all credentials, domain user passwords, and session cookies active on the system during the Frethog execution timeframe.

What to Avoid

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

1. Do not assume the incident is resolved simply because an antivirus tool removed the initial Frethog dropper; always verify that secondary payloads and persistence hooks have been eradicated.
2. Avoid logging in with Domain Admin or privileged credentials on a machine suspected of running Frethog until memory triage is complete.
3. Do not delay host isolation; automated lateral movement and credential dumping can occur within minutes of initial execution.

References & External Analysis

• Search "frethog" on VirusTotal (External Analysis)
• Search "frethog" on Any.Run (Sandbox Sandbox)
• Search "frethog" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Mmxmr
• Rvrat
• Socstealer
• Xxybvi
• Casinoonline
• Mozla
• Volt
• Vbcryptent

Machine-readable

Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/frethog.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.