Overview

TrojanDropper:Win32/PrepScram is a highly obfuscated, targeted trojan dropper utilized to securely deliver and execute secondary payloads while evading traditional antivirus defenses.

What is PrepScram?
For the end-user, PrepScram is entirely invisible, operating silently in the background. For threat intelligence analysts, PrepScram represents a sophisticated staging mechanism. It is heavily packed and utilizes dynamic API resolution to hide its true intentions from static scanners. Its sole purpose is to establish a foothold, decrypt a hidden payload (often embedded within its own binary or downloaded securely), and execute it directly in memory.

Infection Vectors & Threat Hunting
PrepScram is frequently utilized in highly targeted spearphishing campaigns, often dropped by weaponized Office documents containing malicious VBA macros. Upon execution, PrepScram performs extensive environment checks to ensure it is not running in a sandbox or debugger (e.g., checking for VMware/VirtualBox artifacts or specific EDR hooks). Once validated, it allocates memory in a legitimate process (like explorer.exe) and uses techniques like Process Hollowing to inject and execute the final payload, which is often a RAT or banking trojan.

Forensic Analysis & Impact
The impact of PrepScram is entirely dependent on the secondary payload it delivers. Incident responders should hunt for EDR alerts related to 'Process Hollowing' or 'Suspicious Memory Allocation'. Memory forensics is absolutely critical; analysts must dump the memory of the hollowed process to extract the unencrypted secondary payload, as it never touches the disk. Dropped, highly entropic (packed) files in the %AppData% directory are also strong IoCs.

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to the MITRE ATT&CK framework:

Technique	Name	Tactic
`T1055.012`	Process Injection: Process Hollowing	Defense Evasion
`T1027.002`	Obfuscated Files or Information: Software Packing	Defense Evasion
`T1497.001`	Virtualization/Sandbox Evasion: System Checks	Defense Evasion
`T1129`	Shared Modules	Execution
`T1105`	Ingress Tool Transfer	Command and Control

Generated Detections (Boilerplate)

These YARA and Sigma rules are auto-generated based on the family name and aliases. They must be heavily tuned before deployment in a production environment.

YARA Rule

rule MALWARE_WIN_PREPSCRAM {
    meta:
        description = "Detects Prepscram (trojan_generic)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "prepscram" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Prepscram Activity
id: fe4b6137ff8c30dd14cbed68b93fa64c
status: experimental
description: Detects generic indicators of the prepscram malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*prepscram*"
    condition: selection
level: medium

Containment & Response Steps

Ordered checklist for responders. Adapt to your environment and engage professional support for active incidents.

Isolate the endpoint immediately to prevent the secondary, memory-resident payload from establishing C2 communications or moving laterally.
Perform a live memory capture (e.g., using WinPmem) before powering down the machine to ensure the hollowed process payload can be extracted.
Analyze the initial infection vector (e.g., the spearphishing email) to determine the scope of the targeted attack.
Force a password reset for the compromised user and rebuild the OS from a known-good image.

What to Avoid

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

Do not reboot the machine before capturing memory; the secondary payload exists solely in RAM and will be lost, hindering the investigation.
Avoid relying on static file analysis of the PrepScram dropper, as the heavy packing and obfuscation will yield minimal intelligence.

Prepscram

Overview

MITRE ATT&CK Techniques

Generated Detections (Boilerplate)

YARA Rule

Sigma Rule

Containment & Response Steps

What to Avoid

References & External Analysis

Related Families (Category: trojan_generic)

Machine-readable

Ecosystem & Interactive Environments