Extinstaller

Overview

Adware:Win32/Extinstaller is a classification for deceptive software components specifically designed to forcibly install unwanted, malicious, or ad-supported browser extensions into Chrome, Firefox, or Edge. It operates as a local privilege escalation and persistence mechanism, ensuring that even if a user deletes the extension from their browser, the local service will simply reinstall it (`T1189`).

Understanding Extinstaller (Browser Hijackers)
To an end-user, Extinstaller causes a highly frustrating browsing experience: homepages are changed, default search engines are hijacked, and web pages are injected with unwanted advertisements. For a security team, it represents a risk to corporate data, as these forced extensions often monitor all web traffic, capture search queries, and can potentially steal session cookies or credentials (`T1111`).

Execution and Persistence Mechanics
Extinstaller is typically bundled with freeware or pirated software. Upon execution, it does not rely on the browser's web store. Instead, it interacts directly with the browser's local configuration files or the Windows Registry. For Chrome, it often abuses the `ExtensionInstallForcelist` enterprise policy (`T1562.001`), locking the extension so the user cannot click 'Remove'. It establishes an OS-level persistence mechanism (a Scheduled Task or Registry Run key) (`T1547.001`) that constantly checks if the malicious extension is active and re-injects it if it has been removed.

Indicators of Compromise & Impact
The primary impact is privacy violation, browser hijacking, and exposure to malvertising. Host-based IoCs include unauthorized modifications to the `HKLM\Software\Policies\Google\Chrome\ExtensionInstallForcelist` registry key, the presence of anomalous scheduled tasks running scripts or unknown executables, and the physical presence of unpacked extension files in `%LocalAppData%` outside the normal browser extension directories. Network IoCs involve constant background beaconing to advertising affiliate networks.

MITRE ATT&CK Techniques

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

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_EXTINSTALLER {
    meta:
        description = "Detects Extinstaller (advanced_threat)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "extinstaller" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Extinstaller Activity
id: 2205ab1fa170e3d6e8219aab6bae4abc
status: experimental
description: Detects generic indicators of the extinstaller malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*extinstaller*"
    condition: selection
level: medium

Containment & Response Steps

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

1. Use an enterprise-grade Adware removal tool to locate and destroy the OS-level persistence mechanisms (the 'reinstaller' service).
2. Manually remove the malicious registry keys enforcing the `ExtensionInstallForcelist` policy in Windows.
3. Reset the affected web browsers to their default settings to clear out the malicious extension files and restore normal search behavior.
4. Implement endpoint application control to prevent users from executing unvetted, bundled software installers.

What to Avoid

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

1. Do not rely solely on removing the extension from within the browser's UI; Extinstaller is designed to defeat this action.
2. Avoid ignoring adware infections in a corporate environment; malicious extensions can easily capture sensitive web application data.

References & External Analysis

• Search "extinstaller" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: advanced_threat)

Explore other malware families in the same category:

• Spyboter
• Brosafe
• Invader
• Monder
• Stalk

Machine-readable

Get this profile as JSON: https://jordan123234-malware-families-explorer.static.hf.space/api/extinstaller.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.