Bersek

Overview

Bersek is an intricate malware strain primarily characterized by its capabilities as a backdoor and information stealer. It infiltrates systems typically via social engineering campaigns, malicious email attachments, or drive-by downloads. Once inside, Bersek immediately establishes a hidden presence, often manipulating system services to ensure it runs continuously. The malware is designed to harvest sensitive data, including login credentials, financial information, and personal documents, which it then exfiltrates to attacker-controlled servers. Furthermore, Bersek has the capacity to download and execute secondary payloads, effectively turning the compromised machine into a node for further malicious activities, such as participating in botnets or distributing spam. Its modular nature and use of strong encryption for command and control communications make it a persistent and dangerous threat to enterprise environments.

Known aliases

Threat reports may refer to this family under multiple names:

• Bersek Backdoor

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: Win32_Bersek_Backdoor_Engine

Known Derivatives & Downstream Variants: Bersek.A · Bersek.Gen · Win32.Bersek

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: Monitor for unauthorized keylogging, screen capturing, or web browser API hooking. Deploy EDR to detect API hooking.
• T1059: Restrict execution of scripting languages such as PowerShell, VBScript, or Python to authorized administrators. Enforce Script Block Logging.
• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.

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.

• 29e0f1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b7c8d9e0
• 3af1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b7c8d9e0f1

Delivery vectors

• Compromised freeware distribution mirrors and malicious email attachments
• Automated exploitation of unpatched Windows RPC interfaces (CVE-2003-0352)

Persistence mechanisms

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\BersekService
• System registry Shell spawning hook under Winlogon

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_BERSEK_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Bersek"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "bersek" ascii wide nocase
        $s2 = "bersek backdoor" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Bersek (Backdoor) Execution & Triage
id: de90e7a6-ccb1-5137-a4e3-80d109311a24
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Bersek malware family. Detects proxy execution, reflective DLL loading,
  and remote command injection associated with modular enterprise backdoors.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/bersek
- 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.backdoor
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1056
- attack.t1059
- attack.t1543
- attack.t1105
- attack.t1043
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \powershell.exe
    - \cmd.exe
    - \rundll32.exe
    - \regsvr32.exe
    CommandLine|contains:
    - DownloadString
    - IEX(
    - '/s /n /u /i:'
    - sc create
    - start-process
  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_BERSEK_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Bersek 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 = "bersek" 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 affected endpoints from the network immediately to sever unauthorized command and control communication.
2. Identify and terminate active Bersek binaries and associated parent-child process chains.
3. Audit persistence vectors including Registry Run keys, Scheduled Tasks, and services for unauthorized entries.
4. Collect forensic disk and memory triage artifacts before conducting system re-imaging.

What to Avoid

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

1. Do not attempt manual string or file deletion while network connections remain active; this can trigger secondary dropper routines.
2. Avoid restoring from backups without verifying that the backup snapshot predates initial Bersek installation.

References & External Analysis

• Kaspersky Cyberthreat Glossary - Backdoor.Win32.Bersek
• NIST National Vulnerability Database - CVE-2004-0120
• Search "bersek" on VirusTotal (External Analysis)
• Search "bersek" on Any.Run (Sandbox Sandbox)
• Search "bersek" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Backdoor)

Explore other documented threats in the same operational category:

• Werpoapt
• Opanki
• Keydoor
• Tick
• Zxshell
• Shadowhammer
• Noancooe
• Adodb

Machine-readable

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