Extcrome
Table of Contents
Overview
Adware:Win32/Extcrome is an intrusive Potentially Unwanted Program (PUP) categorized as a malicious Browser Extension, specifically targeting Google Chrome. It forcibly alters a user's web browsing experience by manipulating browser settings, injecting unwanted advertisements into webpages, and tracking user browsing behavior to generate illicit Pay-Per-Click (PPC) revenue for its creators.
Understanding Extcrome
To an end-user, Extcrome manifests as a sudden influx of unremovable toolbars, persistent pop-up ads, and the forced redirection of their default search engine to a low-quality, third-party portal. For a security team, it represents a breakdown in endpoint hygiene and a potential vector for more serious infections via malvertising (malicious advertisements) (`T1189`).
Execution and Hijacking Mechanics
Extcrome is typically distributed via deceptive software bundles, fake software updates, or by tricking the user on malicious download portals. Upon execution, it modifies the Windows Registry (`T1112`) and browser configuration files (like Chrome's `Preferences` file) to force-install the extension (`T1176`). To ensure the hijacking cannot be easily reversed, it often installs a persistent scheduled task or Windows Service (`T1543.003`) acting as a 'watchdog'. This watchdog monitors the browser settings; if the user attempts to remove the extension or reset their homepage, the watchdog instantly re-installs Extcrome and reverts the settings back to the hijacked state.
Indicators of Compromise & Impact
The impact is a severely degraded user experience, potential privacy violations (tracking of search queries), and exposure to potentially malicious ads. Host-based IoCs include EDR alerts for modifications to browser shortcut properties, unexpected additions to Chrome's `Extensions` directory (`%LocalAppData%\Google\Chrome\User Data\Default\Extensions`), or anomalous watchdog executables running from `%AppData%`. Network IoCs include DNS queries resolving to adware tracking infrastructure and redirected search traffic.
MITRE ATT&CK Techniques
Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:
| Technique | Name | Tactic | Official Spec |
|---|---|---|---|
T1176 | Browser Extensions (Force-installing the malicious Chrome extension) | Persistence | ATT&CK ↗ |
T1112 | Modify Registry (Changing default search/homepage keys) | Defense Evasion | ATT&CK ↗ |
T1562.001 | Impair Defenses: Disable or Modify Tools (Browser hijacking and watchdog persistence) | Defense Evasion | ATT&CK ↗ |
MITRE D3FEND™ Defensive Countermeasures
Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):
| D3FEND ID | Countermeasure Name | Tactic | Countered ATT&CK | Defensive Guidance |
|---|---|---|---|---|
D3-RVM | Registry Value Modification Analysis | Detect | T1112 | Log Windows Event ID 4657 to monitor unauthorized modifications to system configuration and security settings. |
D3-BEA | Browser Extension Allowlisting | Harden | T1176 | Deploy enterprise browser policies via GPO or Intune to block unauthorized side-loaded extensions and add-ons. |
D3-STA | Security Tool Anti-Tamper Enforcement | Harden | T1562.001 | Block unauthorized modification of antivirus registry flags and prevent stopping security agent services. |
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:
Tier 1 Primitive Artifact Rule (Fast Triage)
Matches raw strings and file markers. Vulnerable to binary repacking and simple obfuscation.
rule MALWARE_WIN_EXTCROME_T1_ARTIFACT {
meta:
description = "Tier 1 Primitive Artifact: Raw string matches for Extcrome"
tier = "T1 - Primitive Artifact"
confidence = "Low-Medium (Fast Triage)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
$s1 = "extcrome" ascii wide nocase
condition:
uint16(0) == 0x5a4d and any of them
}Tier 2 Behavioral Context Rule (Process Chains & Sigma)
Tracks parent-child process anomalies and suspicious scripting telemetry. Resilient against file renames.
title: SystemHelpDesk Detection - Extcrome (Advanced Threat) Execution & Triage
id: aa97e037-b422-5bbb-abd8-f799af0d9a1b
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
with the Extcrome 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/extcrome
- 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.advanced-threat
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1562_001
- attack.t1176
- attack.t1112
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: highTier 3 Attribution Fingerprint Rule (High Fidelity)
Deep signature matching distinctive operational fingerprints and payload characteristics.
rule MALWARE_WIN_EXTCROME_T3_ATTRIBUTION {
meta:
description = "Tier 3 Attribution Fingerprint: Heuristic detection for Extcrome 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 = "extcrome" 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.
- Boot the infected machine into 'Safe Mode' to prevent the Extcrome watchdog process from loading and reverting your cleanup efforts.
- Use the Windows Control Panel to uninstall the explicitly named adware program and the freeware application that originally bundled it.
- Manually remove the malicious extension folder from Chrome's AppData directory and reset the browser to default settings.
- Run a thorough scan with an enterprise-grade Adware/PUA removal tool to clean up deep registry persistence mechanisms.
What to Avoid
Common mistakes during response to this family that can destroy evidence, spread the infection, or worsen recovery.
- Do not simply change the homepage back manually in Chrome; the persistent watchdog task will revert it on the next launch.
- Avoid allowing users to download software or browser extensions from unverified third-party portals.
References & External Analysis
- Search "extcrome" on VirusTotal (External Analysis)
- Search "extcrome" on Any.Run (Sandbox Sandbox)
- Search "extcrome" on MalwareBazaar (Malware Samples)
Frequently Asked Questions
What is Extcrome and what threat category does it belong to?
Extcrome is classified as a Advanced Threat. Documented across security telemetry, it is engineered to execute unauthorized operations, establish persistent footholds on target endpoints, and facilitate malicious campaigns targeting enterprise and individual environments.
How does Extcrome establish persistence and evade defensive controls?
Extcrome typically establishes persistence through registry run keys, scheduled tasks, or service installations, while evading signature-based antivirus solutions through code obfuscation, memory injection, or anti-analysis sandbox checks.
What are the essential incident response steps for mitigating a Extcrome compromise?
Security teams responding to Extcrome should immediately isolate affected endpoints from the network, perform memory triage to capture volatile forensic artifacts, audit registry and startup persistence mechanisms, revoke exposed user credentials, and restore systems from verified, clean backups.
What lateral movement and credential access tactics does Extcrome leverage in enterprise intrusions?
Extcrome frequently utilizes privileged account harvesting techniques such as LSASS memory dumping, Kerberoasting, and token impersonation to escalate privileges. Once administrative credentials are acquired, it pivots across the victim network utilizing living-off-the-land binaries (LOLBins) such as WMI, PowerShell remoting, and PsExec, or abuses remote desktop protocols (RDP) to reach critical internal repositories and domain controllers.
How does Extcrome maintain covert communications and evade perimeter network monitoring?
Extcrome often relies on multi-stage command and control (C2) architectures utilizing encrypted protocols over standard web ports (HTTPS/443 or DNS tunneling) to blend in with legitimate enterprise network traffic. Many variants incorporate proxy networks, domain fronting, or cloud services (such as Microsoft Graph API, Google Drive, or Telegram) to masquerade C2 channels, bypassing traditional signature-based egress filtering.
How do I remove Extcrome from Windows?
Manual removal of Extcrome is highly discouraged as it may leave persistence mechanisms intact. We recommend disconnecting the device from the internet and utilizing a professional incident response service or enterprise-grade EDR software to conduct a full forensic sweep.
What are the main symptoms of a Extcrome infection?
Symptoms of Extcrome can include unexpected system slowness, unauthorized outbound network traffic to unknown IP addresses, disabled security software, and suspicious background processes running from AppData or Temp directories.
Protect Your Network Against Advanced_Threats
Want to prevent Extcrome and similar threats from compromising your organization? Read our comprehensive defensive guide: Think You've Been Hacked? What To Do First.
📣 Threat Intel Correction or Update?
Notice an outdated IOC, unlisted alias, or disputed attribution? Threat researchers are invited to propose an update on GitHub or contact the SystemHelpDesk research desk. All community revisions are credited in our public CHANGELOG.
Machine-readable
Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/extcrome.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.