Jackservn

Overview

Jackservn (classified in antimalware definitions under Trojan:Win32/Jackservn, TrojanDownloader:Win32/Jackservn, and Backdoor:Win32/Jackservn) is a stealthy modular trojan downloader and stager engineered to establish a persistent bridgehead on Windows systems and retrieve follow-on malicious packages. Disseminated primarily through malicious email attachments, deceptive software installers, and drive-by download vectors, Jackservn executes initial environment reconnaissance upon initial execution. It interrogates the operating system version, processor architecture, active defensive processes, and checks for virtualized hypervisors or debugger hooks to evade sandbox analysis. Once evasion checks succeed, Jackservn drops an executable binary into `%APPDATA%` or `%LOCALAPPDATA%` and creates a persistent Windows service or Scheduled Task for survivability across reboots. The trojan subsequently initiates HTTPS POST beacons to remote command-and-control servers, transmitting endpoint telemetry and receiving encrypted instructions to download, unpack, and launch secondary payloads, including banking trojans, info-stealers, and cryptominers.

Known aliases

Threat reports may refer to this family under multiple names:

• Trojan:Win32/Jackservn
• TrojanDownloader:Win32/Jackservn
• Win32/Jackservn
• Jackservn Loader
• Trojan.Jackservn

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):

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_JACKSERVN_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Jackservn"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "jackservn" ascii wide nocase
        $s2 = "trojan:win32/jackservn" ascii wide nocase
        $s3 = "trojandownloader:win32/jackservn" ascii wide nocase
        $s4 = "win32/jackservn" ascii wide nocase
        $s5 = "jackservn loader" ascii wide nocase
        $s6 = "trojan.jackservn" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Jackservn (Trojan Downloader) Execution & Triage
id: 5f50fa2a-2bec-56ff-8a83-7e5d2a89e2e8
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Jackservn 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/jackservn
- https://malware-families-catalog.systemhelpdesk.com/defensive/ransomware-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-downloader
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1105
- attack.t1059_003
- attack.t1543_003
- attack.t1053_005
- attack.t1497_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_JACKSERVN_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Jackservn 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 = "jackservn" 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. Isolate the endpoint immediately to prevent Jackservn from downloading and executing its secondary payloads (e.g., ransomware).
2. Audit the Windows Task Scheduler and Registry Run keys to identify and remove the Jackservn persistence mechanisms.
3. Review firewall and proxy logs to identify the C2 domains Jackservn attempted to contact, and block them enterprise-wide.
4. Capture a live memory image (RAM dump) to extract the injected Jackservn modules and identify the secondary payloads.

What to Avoid

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

1. Do not close an incident simply because the initial Jackservn dropper was quarantined; always verify if secondary payloads were downloaded.
2. Avoid relying solely on manual file deletion, as the injected processes will likely just recreate the dropped binaries.

References & External Analysis

• Microsoft Defender Security Intelligence - Trojan:Win32/Jackservn
• Sophos Threat Center - Trojan.Jackservn Analysis
• MITRE ATT&CK - Ingress Tool Transfer (T1105)
• Search "jackservn" on VirusTotal (External Analysis)
• Search "jackservn" on Any.Run (Sandbox Sandbox)
• Search "jackservn" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan Downloader)

Explore other documented threats in the same operational category:

• Centrumdownloader
• Centrumloader
• Stubrc
• Bsdownloader
• Pidgeon
• Scrop
• Zippyloader
• Slugin

Machine-readable

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