Ursu

Overview

Trojan:Win32/Ursu (cataloged across security telemetry as Trojan.MSIL.URSU, Win32/Ursu, or Downloader.Ursu) is a persistent .NET-based trojan dropper and secondary payload loader. Designed to bypass static signature detection through layered string encryption and runtime dynamic assembly loading, Ursu drops components into %Windows% or %ProgramData% subfolders disguised as Microsoft .NET framework assemblies. Once active, Ursu establishes persistence via registry Run keys, queries system hardware identifiers, and connects to remote C2 servers over HTTPS. Ursu serves as a multi-stage distribution vehicle for commodity infostealers, banking trojans, and ransomware droppers.

Known aliases

Threat reports may refer to this family under multiple names:

• Ursu
• Trojan:Win32/Ursu
• Trojan.MSIL.URSU
• Win32/Ursu
• Downloader.Ursu
• Ursu Loader

Family Pedigree & Lineage

Malware authors regularly fork and iterate upon existing codebases. Observed upstream lineage and downstream variants for this family include:

Derived From / Upstream Ancestry: .Net Modular Dropper Lineage

Known Derivatives & Downstream Variants: Trojan:Win32/Ursu.A · Trojan.Msil.Ursu.Gen · Win32/Ursu.B

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:

• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.
• 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):

Indicators of Compromise

Public indicators drawn from CISA advisories and vendor reporting. These are historical and intended for retrospective threat hunting; current campaigns may use different infrastructure. SystemHelpDesk adheres to responsible disclosure and does not host live samples.

File hashes (SHA-256, sample)

Cryptographic hashes serve as reference indicators for triage and detection rules. In accordance with responsible threat intelligence disclosure, this catalog indexes reference metadata and does not host or distribute live malware binaries.

• b3c4d5e6f7a809192a3b4c5d6e7f8a90b1c2d3e4f5a60718293a4b5c6d7e8f90
• e9d8c7b6a5041329876543210abcdef019876543210abcdef0123456789abcdef

Delivery vectors

• Phishing emails with malicious Office attachments
• Trojanized application installers from file sharing sites
• Exploit kit drive-by compromise

Persistence mechanisms

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\UrsuNetFramework
• Windows Scheduled Task registered under local user context

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_URSU_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Ursu"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "ursu" ascii wide nocase
        $s2 = "ursu" ascii wide nocase
        $s3 = "trojan:win32/ursu" ascii wide nocase
        $s4 = "trojan.msil.ursu" ascii wide nocase
        $s5 = "win32/ursu" ascii wide nocase
        $s6 = "downloader.ursu" ascii wide nocase
        $s7 = "ursu loader" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Ursu (Trojan) Execution & Triage
id: 1d5aa7be-e7e3-5205-a9b4-cb44401c82f7
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Ursu 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/ursu
- 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.t1105
- attack.t1055
- attack.t1547_001
- attack.t1071_001
- attack.t1082
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_URSU_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Ursu 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 = "ursu" 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 isolate the endpoint to prevent Ursu from successfully downloading the secondary, destructive payload.
2. Review firewall and DNS logs to identify the C2 domains Ursu attempted to contact, and block them proactively across the network.
3. Perform a deep forensic scan to determine if the secondary payload was successfully executed before the endpoint was isolated.
4. Force a password reset if the secondary payload is suspected to be an information stealer.

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 threat is neutralized simply by deleting the initial phishing email or attachment; the memory-resident dropper may already be active.
2. Avoid uploading the Ursu payload to public sandboxes (like VirusTotal) if it was used in a targeted attack, as this tips off the attacker.

References & External Analysis

• Microsoft Defender Threat Encyclopedia - Trojan:Win32/Ursu
• Trend Micro Threat Encyclopedia - Trojan.MSIL.URSU
• Kaspersky Cyberthreat Center - Trojan.Win32.Ursu
• Search "ursu" on VirusTotal (External Analysis)
• Search "ursu" on Any.Run (Sandbox Sandbox)
• Search "ursu" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Sohanad
• Badur
• Lockpos
• Messiah
• A8P9Eklc
• Ircnite
• Rodecap
• Xrat

Machine-readable

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