Chopper

Overview

Chopper (widely tracked across cybersecurity research, CISA advisories, and EDR platforms as China Chopper, Backdoor:Win32/Chopper, and Trojan:ASP/Chopper) is a legendary, ultra-compact webshell and remote administration platform first documented in 2012. Measuring as small as 4 kilobytes (or a single line of text, e.g., eval(request("cmd")) in ASPX or eval($_POST["cmd"]) in PHP), Chopper delivers full server management capabilities when paired with its specialized Windows GUI client (chopper.exe). The Windows client interacts with the server-side payload over standard HTTP POST requests, enabling operators to browse and manipulate the remote filesystem, execute interactive command-line commands, transfer files, dump database contents via embedded SQL query interfaces, and initiate lateral movement across corporate networks.

Known aliases

Threat reports may refer to this family under multiple names:

• Backdoor:Win32/Chopper
• China Chopper
• Trojan:ASP/Chopper
• Win32/Chopper
• China Chopper Web Shell

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:

• T1059: Restrict execution of scripting languages such as PowerShell, VBScript, or Python to authorized administrators. Enforce Script Block Logging.
• T1071.001: Implement web filtering and SSL/TLS inspection to detect malicious command and control (C2) traffic hiding in HTTP/HTTPS.

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_CHOPPER_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Chopper"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "chopper" ascii wide nocase
        $s2 = "backdoor:win32/chopper" ascii wide nocase
        $s3 = "china chopper" ascii wide nocase
        $s4 = "trojan:asp/chopper" ascii wide nocase
        $s5 = "win32/chopper" ascii wide nocase
        $s6 = "china chopper web shell" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Chopper (Backdoor) Execution & Triage
id: 71ce2624-55fc-5c9c-a85e-5a8bab540459
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Chopper 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/chopper
- 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.t1505_003
- attack.t1059_003
- attack.t1059_001
- attack.t1071_001
- attack.t1083
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_CHOPPER_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Chopper 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 = "chopper" 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 compromised web server from the internal network immediately to prevent lateral movement, but keep it online to capture live traffic logs.
2. Analyze IIS/Apache access logs to identify the exact file path of the web shell (look for high volumes of POST requests to a specific file).
3. Review the web server process execution logs (EDR) to identify what commands the attacker executed via `cmd.exe` or `powershell.exe`.
4. Once the shell is located, remove the malicious code, but more importantly, identify and patch the initial vulnerability that allowed the upload (e.g., an unpatched CMS plugin).

What to Avoid

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

1. Do not simply delete the web shell file and put the server back into production; the attacker will immediately exploit the same vulnerability to upload a new shell.
2. Avoid relying solely on file-based antivirus to find web shells; a one-line PHP `eval()` statement is often not flagged as malicious by static scanners.

References & External Analysis

• CISA Alert (AA21-200a) - China Chopper Web Shell Analysis
• Microsoft Defender Threat Encyclopedia - Backdoor:Win32/Chopper
• MITRE ATT&CK - Server Software Component: Web Shell (T1505.003)
• CISA Advisory: https://www.cisa.gov/news-events/cybersecurity-advisories/aa21-200a
• Search "chopper" on VirusTotal (External Analysis)
• Search "chopper" on Any.Run (Sandbox Sandbox)
• Search "chopper" on MalwareBazaar (Malware Samples)

North American Authority Advisory (CISA / NIST)

The Cybersecurity and Infrastructure Security Agency (CISA) has published an official US federal advisory on this family, which can be mapped to NIST Cybersecurity Framework (CSF) incident response controls: https://www.cisa.gov/news-events/cybersecurity-advisories/aa21-200a ↗

Frequently Asked Questions

Related Threats (Category: Backdoor)

Explore other documented threats in the same operational category:

• Orcus
• Redcap
• Xiclog
• Teamviewer
• Swrort
• Winvnc
• Back_Orifice
• Doublefantasy

Machine-readable

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