MedusaHVNC Malware Uses Hidden Windows Desktops to Evade Detection

1. Executive summary

MedusaHVNC is a remote access trojan (RAT) offered as malware-as-a-service (MaaS) and promoted via a dedicated website and Telegram channel. The malware employs a 5-stage infection chain culminating in a payload that creates a hidden Windows desktop, from which it launches legitimate browsers (Chrome, Edge, Firefox) to conduct covert activity invisible to the logged-in user. Analysis by BlackFog (single-sourced; verify before enforcement) confirms a hardcoded C2 endpoint at 51.89.204.28:4444 and persistence via a .bat file in the Windows Startup folder. No CISA-KEV exploitation state or CVSS score applies to this item. EMEA financial services should treat this as a stealthy persistent threat where standard user-session monitoring will fail to detect operator activity.

2. Regulatory framing

No specific DORA/NIS2 article is directly engaged by this item. The existence of a malware threat does not, by itself, trigger a distinctive obligation under the articles in scope. If a MedusaHVNC infection is confirmed within a client environment, DORA Art. 18 (classification of ICT-related incidents and cyber threats) and DORA Art. 19 (reporting of major ICT-related incidents to competent authorities) would be engaged by the incident itself — but that trigger is contingent on confirmation, not on this advisory.

3. Technical analysis & attack chain

Attribution caveat: No named threat actor is identified in the source material. No MITRE ATT&CK profile is available. The MaaS operation is promoted through its own website and a Telegram channel; the technical analysis originates solely from BlackFog (single-sourced; verify before enforcement).

Attack chain (confirmed from source)

1. Initial execution: wscript.exe executes a JScript launcher. The script waits approximately 7.5 seconds before proceeding.
2. Staging: The script writes embedded files to %TEMP%\Nx2981Okkr2\, including an encrypted payload and a .bat file placed in the Windows Startup folder for persistence.
3. Decryption via AutoIT: Windows AutoIT is invoked to decrypt the payload and launch charmap.exe (legitimate Windows Character Map). The loader now runs inside the charmap.exe process.
4. In-memory decryption (two layers): - Layer 1: 16-byte repeating XOR applied to 1,009,152 bytes from the .data section. - Layer 2: ChaCha20 decryption of 998,912 bytes of ciphertext using a 32-byte key, a 12-byte nonce, and an initial counter value of 1.
5. Final payload: An unsigned PE32+ x86-64 console executable containing a .pay section and the family string MedusaHVNC. The payload communicates with a hardcoded C2 at 51.89.204.28:4444.

Malware capabilities (from the HVNC module)

• Creates a hidden Windows desktop and launches a legitimate browser (Chrome, Edge, or Firefox) within it. All browser activity is invisible to the user on the active desktop.
• Screen/window capture: Uses Win32 API functions BitBlt, EnumWindows, and PrintWindow.
• Synthetic input: Uses SendInput and SetWindowsHookExW for simulated keystrokes/mouse interaction.
• Clipboard manipulation: Uses OpenClipboard, GetClipboardData, and SetClipboardData to move data into or out of the session.
• C2 communication: Hardcoded IP and port (51.89.204.28:4444); protocol not specified in the source.

Persistence: .bat file in the Windows Startup folder ensures the malware survives reboot.

Key evasion characteristic: Because all operator activity occurs on a hidden desktop using legitimate browser and Windows binaries, endpoint user-session monitoring and screen-capture-based surveillance will not observe the attacker's actions. The source notes that the only obvious detection surface is unexpected data exfiltration leaving the network.

4. Mitigation & containment

P1 — Within 24 hours

• Block C2: Add 51.89.204.28 to firewall egress deny rules and EDR network containment lists. Block outbound traffic to port 4444 where feasible.
• Hunt for persistence: Check all endpoints for unexpected .bat files in the Startup folder (%APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup\ and C:\ProgramData\Microsoft\Windows\Start Menu\Programs\StartUp\).
• Hunt for staging directory: Search for %TEMP%\Nx2981Okkr2\ across endpoints.
• Monitor for process abuse: Alert on wscript.exe spawning charmap.exe and on charmap.exe making outbound network connections — this is anomalous behaviour for the Windows Character Map utility.

P2 — Within 72 hours

• EDR detection rules: Deploy detection for charmap.exe loading AutoIT-related modules or exhibiting network activity. charmap.exe is a GUI utility with no legitimate need for network connectivity.
• Restrict wscript.exe: Where business requirements allow, disable or restrict wscript.exe via Application Control / WDAC / AppLocker to prevent JScript launcher execution.
• Monitor clipboard API abuse: Alert on unexpected processes calling SetClipboardData and GetClipboardData in sequence, particularly from processes that should not interact with the clipboard.
• Network egress monitoring: The source explicitly identifies data exfiltration detection as the primary mitigation. Review NetFlow/proxy logs for unexpected outbound data transfers, particularly from workstations during non-business hours.

P3 — Within 7 days

• AutoIT restriction: If AutoIT is not a business requirement, block autoit3.exe execution via application whitelisting.
• HVNC detection: Alert on processes calling CreateDesktop / SetThreadDesktop Win32 APIs followed by browser process creation — this is indicative of hidden virtual desktop creation.
• Threat hunt: Search endpoint telemetry for the 5-stage chain signature: wscript.exe → file write to %TEMP% → .bat creation in Startup → charmap.exe execution with network activity.

5. Indicators of compromise

ipv4  51.89.204.28
port  4444
filepath  %TEMP%\Nx2981Okkr2\
file  .bat in Windows Startup folder
process  wscript.exe executing JScript
process  charmap.exe with network activity
pe_section  .pay
string  MedusaHVNC

Behavioural indicators

6. Detection

rule MedusaHVNC_RAT {
    meta:
        author = "Adverse Trace"
        date = "2026-07-27"
        reference = "https://www.securityweek.com/medusahvnc-malware-uses-hidden-windows-desktops-to-evade-detection/"
        description = "Detects MedusaHVNC RAT payload by family string and .pay section"

    strings:
        $family = "MedusaHVNC" ascii
        $section = ".pay" ascii

    condition:
        $family and $section
}

title: MedusaHVNC Infection Chain - wscript.exe Spawning charmap.exe
id: 7a3c1f2e-4b5d-4a8e-9c1f-0a6b2c3d4e5f
status: experimental
description: Detects wscript.exe spawning charmap.exe, consistent with the MedusaHVNC 5-stage infection chain
author: Adverse Trace
date: 2026/07/27
references:

    - https://www.securityweek.com/medusahvnc-malware-uses-hidden-windows-desktops-to-evade-detection/
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        ParentImage|endswith: '\wscript.exe'
        Image|endswith: '\charmap.exe'
    condition: selection
level: high

title: MedusaHVNC C2 Communication - charmap.exe Network Connection
id: 8b4d2g3f-5c6e-4b9f-0d2g-1b7c3d4e5f6a
status: experimental
description: Detects charmap.exe making network connections to the hardcoded MedusaHVNC C2
author: Adverse Trace
date: 2026/07/27
references:

    - https://www.securityweek.com/medusahvnc-malware-uses-hidden-windows-desktops-to-evade-detection/
logsource:
    category: network_connection
    product: windows
detection:
    selection_process:
        Image|endswith: '\charmap.exe'
    selection_c2:
        DestinationIp: '51.89.204.28'
        DestinationPort: 4444
    condition: selection_process and selection_c2
level: critical

title: MedusaHVNC Persistence - BAT File in Startup Folder
id: 9c5e3h4g-6d7f-4c0a-1e3h-2c8d4e5f6a7b
status: experimental
description: Detects .bat file creation in Windows Startup folder, consistent with MedusaHVNC persistence
author: Adverse Trace
date: 2026/07/27
references:

    - https://www.securityweek.com/medusahvnc-malware-uses-hidden-windows-desktops-to-evade-detection/
logsource:
    category: file_event
    product: windows
detection:
    selection:
        TargetFilename|contains:

            - '\Microsoft\Windows\Start Menu\Programs\Startup\'
        TargetFilename|endswith: '.bat'
    condition: selection
level: high

7. Sources

• SecurityWeek, "MedusaHVNC Malware Uses Hidden Windows Desktops to Evade Detection," https://www.securityweek.com/medusahvnc-malware-uses-hidden-windows-desktops-to-evade-detection/, 2026-07-27

8. Adverse Trace position

MedusaHVNC presents a moderate-to-high risk to EMEA financial services endpoints. Its use of legitimate Windows binaries (charmap.exe, wscript.exe, AutoIT) and a hidden desktop makes it inherently difficult to detect through user-session monitoring or behavioural analytics focused on the active desktop. The hardcoded C2 (51.89.204.28:4444) provides an immediate, actionable block, but the MaaS distribution model means the C2 address is likely to rotate across campaigns. The 5-stage infection chain offers multiple detection opportunities at the process-creation and file-write layers, which we have codified in the Sigma rules above. Attribution is unconfirmed — no actor is named in the source material, and the technical analysis is single-sourced from BlackFog. We will monitor for additional corroboration, new C2 infrastructure, and any IOCs from active deployments. Clients should prioritise P1 network blocking and endpoint hunting for the staging path and Startup-folder persistence mechanism.

Read the original source →

Published via PulseTrace — Adverse Trace threat intelligence.