Dorifel

Overview

Dorifel (also known as Quervar and classified across antivirus vendors under signatures including Trojan:Win32/Dorifel, Virus:Win32/Dorifel.A, and Worm:Win32/Dorifel) is a landmark polymorphic file infector, worm, and banking downloader first discovered in 2012 targeting European financial and government networks. Propagated via spearphishing emails containing malicious Word documents, network shares, and removable USB drives, Dorifel infects existing Microsoft Office documents (Word .doc and Excel .xls) and executable files. It prepends or encrypts original file content, embedding a malicious loader stub so that opening a legitimate document executes the trojan. Dorifel establishes encrypted communications with remote command-and-control servers, downloading secondary banking trojans such as Citadel and Zeus to capture financial credentials.

Known aliases

Threat reports may refer to this family under multiple names:

• Trojan:Win32/Dorifel
• Virus:Win32/Dorifel
• Worm:Win32/Dorifel
• Win32/Quervar
• Virus:Win32/Dorifel.A

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:

• T1059.003: Restrict execution of Windows Command Shell (cmd.exe) and block unauthorized batch scripts.
• T1071.001: Implement web filtering and SSL/TLS inspection to detect malicious command and control (C2) traffic hiding in HTTP/HTTPS.
• T1566.001: Scan email attachments for malicious macros, scripts, or suspicious archive files.

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_DORIFEL_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Dorifel"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "dorifel" ascii wide nocase
        $s2 = "trojan:win32/dorifel" ascii wide nocase
        $s3 = "virus:win32/dorifel" ascii wide nocase
        $s4 = "worm:win32/dorifel" ascii wide nocase
        $s5 = "win32/quervar" ascii wide nocase
        $s6 = "virus:win32/dorifel.a" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Dorifel (Trojan) Execution & Triage
id: 2ad68977-fc90-5e83-9e7f-c9e972e36b23
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Dorifel 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/dorifel
- 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.t1566_001
- attack.t1059_003
- attack.t1055
- attack.t1547_001
- attack.t1071_001
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_DORIFEL_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Dorifel 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 = "dorifel" 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. Immediately disconnect infected hosts from local networks to prevent file infection spread across network shares.
2. Kill active Dorifel loader processes and quarantine newly created executable stubs.
3. Remove Run keys under HKCU\Software\Microsoft\Windows\CurrentVersion\Run pointing to Dorifel.
4. Deploy specialized file disinfection utilities or restore documents from immutable clean backups.
5. Block identified C2 IP addresses and exfiltration domains across firewalls and web proxies.

What to Avoid

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

1. Do not open Word or Excel documents on unverified endpoints without macro execution protections.
2. Do not simply delete infected documents if user data can be recovered using disinfection tools or backups.

References & External Analysis

• Microsoft Defender Threat Encyclopedia - Trojan:Win32/Dorifel
• Kaspersky Lab - Dorifel (Quervar) Malware Analysis
• Trend Micro Threat Encyclopedia - Worm_Dorifel
• Search "dorifel" on VirusTotal (External Analysis)
• Search "dorifel" on Any.Run (Sandbox Sandbox)
• Search "dorifel" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Shelma
• Hostspatcher
• Agen
• Tibs
• Trjgen
• Wirelessnetview
• Hpursnif
• Ntkrnl

Machine-readable

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