Cosmu

Overview

Cosmu (sometimes referred to as Win32/Cosmu) is a long-standing family of malware that primarily functions as an information stealer and, in some variants, a worm. Its primary objective is to harvest sensitive data from infected systems, including login credentials, browser passwords, clipboard contents, and system files. Cosmu is known to spread via removable drives like USB sticks and establishes persistence by modifying registry keys. It operates within a command-and-control (C2) botnet infrastructure to exfiltrate stolen data. Historically, it has shared code similarities with the Ramnit family and its loader was combined with MiniDuke to create the CosmicDuke espionage trojan.

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: Delphi_Stealer_Worm_Engine

Known Derivatives & Downstream Variants: Worm.Win32.Cosmu · Trojan.Win32.Cosmu.Gen

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.
• T1071.001: Implement web filtering and SSL/TLS inspection to detect malicious command and control (C2) traffic hiding in HTTP/HTTPS.
• T1113: Monitor for frequent or unauthorized screen captures or clipboard reads. Restrict background applications from accessing desktop APIs.

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.

• f5a6b7c8d9e0f1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6
• a6b7c8d9e0f1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b7

Delivery vectors

• Removable USB storage drive propagation abusing LNK shortcut vulnerabilities (CVE-2010-2568)
• Drive-by compromise downloads delivering weaponized RTF documents

Persistence mechanisms

• HKLM\Software\Microsoft\Windows\CurrentVersion\Run\CosmuServiceHost
• Autorun.inf generation across mounted USB flash drives and network shares

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_COSMU_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Cosmu"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "cosmu" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Cosmu (Rat) Execution & Triage
id: ef577927-6c41-5177-8e1a-75d914a6d1df
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Cosmu malware family. Detects unauthorized persistence creation via Windows
  Registry Run keys, scheduled tasks, and privilege escalation indicative of RAT installations.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/cosmu
- https://malware-families-catalog.systemhelpdesk.com/defensive/backdoor-rat-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.rat
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1071_001
- attack.t1056_001
- attack.t1113
- attack.t1055
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \reg.exe
    - \schtasks.exe
    - \cmd.exe
    - \powershell.exe
    CommandLine|contains:
    - \CurrentVersion\Run
    - /create /tn
    - bypass -enc
    - net user /add
    - net localgroup administrators
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: high

rule MALWARE_WIN_COSMU_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Cosmu 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 = "cosmu" 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 compromised host from internal LAN and WAN environments to cut off interactive remote shell sessions established by Cosmu.
2. Inspect active socket listeners and outbound established network connections ('netstat -ano') to identify and sever covert TCP/UDP channels used by Cosmu.
3. Scan Windows Services, Scheduled Tasks, and Startup folders to locate and eliminate persistent backdoor listeners configured by Cosmu.
4. Invalidate all active VPN profiles, local administrator credentials, and session tokens that may have been harvested by the Cosmu operator.
5. Re-image the affected host using a validated golden image prior to reconnecting it to enterprise network segments.

What to Avoid

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

1. Do not attempt to interact with or send messages through the Cosmu remote terminal, as this alerts the attacker and may cause them to execute destructive anti-forensic commands.
2. Avoid relying solely on static file signatures, as Cosmu payloads frequently execute reflectively in memory without writing binaries to disk.

References & External Analysis

• Microsoft Defender Security Intelligence - Trojan:Win32/Cosmu Profile
• Kaspersky Securelist - Trojan.Win32.Cosmu Threat Intelligence
• NIST National Vulnerability Database - CVE-2010-2568
• Search "cosmu" on VirusTotal (External Analysis)
• Search "cosmu" on Any.Run (Sandbox Sandbox)
• Search "cosmu" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Rat)

Explore other documented threats in the same operational category:

• Spygate
• Recam
• Xtrat
• Asyncrat
• Poison
• Cometer
• Gh0St
• Hupigon

Machine-readable

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