Fleercivet
Table of Contents
Overview
Adware:Win32/Fleercivet is a persistent adware family focused on click fraud and silent ad-injection. Unlike traditional adware that constantly bothers the user with visible pop-ups, Fleercivet is designed to operate more stealthily, generating revenue by simulating clicks on background advertisements or by quietly replacing legitimate ads on websites with those belonging to the attacker's affiliate network (`T1499`).
Understanding Fleercivet (Ad Injection)
To an end-user, the infection might manifest as slow browser performance or noticing that ads on familiar websites look strangely off-brand or lower quality. For a security team, Fleercivet is a network nuisance that indicates a failure in endpoint controls regarding Potentially Unwanted Programs (PUPs) and introduces the risk of malvertising.
Execution and Injection Mechanics
Fleercivet is distributed primarily via software bundling. Upon execution, it establishes persistence, often utilizing a Scheduled Task or modifying the `AppInit_DLLs` registry key (`T1546.010`) to ensure its DLL is loaded into every new process (specifically targeting browsers). Once hooked into the browser process (Chrome, Firefox, or Edge), Fleercivet uses Man-in-the-Browser (MitB) techniques to intercept web traffic. It parses the HTML of incoming web pages and dynamically injects its own JavaScript, which replaces existing ad banners or creates invisible iframes to click on ads silently in the background.
Indicators of Compromise & Impact
The impact is degraded system performance and exposure to untrusted advertising networks. Host-based IoCs include EDR alerts for DLL injection into browser processes (e.g., `chrome.exe`), unauthorized modifications to `AppInit_DLLs`, and unexpected Scheduled Tasks. Network IoCs include DNS requests and HTTP traffic directed towards known affiliate marketing and tracking domains that occur independently of user navigation.
MITRE ATT&CK Techniques
Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:
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-RBI | Remote Browser Isolation | Isolate | T1189 | Execute untrusted web browsing sessions in disposable cloud containers to isolate drive-by exploits from local endpoints. |
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_FLEERCIVET_T1_ARTIFACT {
meta:
description = "Tier 1 Primitive Artifact: Raw string matches for Fleercivet"
tier = "T1 - Primitive Artifact"
confidence = "Low-Medium (Fast Triage)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
$s1 = "fleercivet" 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 - Fleercivet (Advanced Threat) Execution & Triage
id: 395ca041-119f-5970-933e-417c59d00e00
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
with the Fleercivet 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/fleercivet
- 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.t1546_010
- attack.t1499
- attack.t1189
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_FLEERCIVET_T3_ATTRIBUTION {
meta:
description = "Tier 3 Attribution Fingerprint: Heuristic detection for Fleercivet 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 = "fleercivet" 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.
- Use a robust anti-malware tool (like Malwarebytes or AdwCleaner) to locate and remove the Fleercivet DLLs and the associated injection registry keys.
- Verify and clean the `AppInit_DLLs` registry key (`HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows`).
- Reset all web browsers to default settings to ensure no malicious extensions were also dropped.
- Educate users on the risks of 'Express Installations' when downloading freeware.
What to Avoid
Common mistakes during response to this family that can destroy evidence, spread the infection, or worsen recovery.
- Do not assume the browser is secure just because no new toolbars are visible; Fleercivet operates largely via injected code, not UI extensions.
- Avoid relying solely on traditional antivirus signatures, as the ad-injection scripts are frequently updated.
References & External Analysis
- Search "fleercivet" on VirusTotal (External Analysis)
- Search "fleercivet" on Any.Run (Sandbox Sandbox)
- Search "fleercivet" on MalwareBazaar (Malware Samples)
Frequently Asked Questions
What is Fleercivet and what threat category does it belong to?
Fleercivet 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 Fleercivet establish persistence and evade defensive controls?
Fleercivet 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 Fleercivet compromise?
Security teams responding to Fleercivet 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 Fleercivet leverage in enterprise intrusions?
Fleercivet 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 Fleercivet maintain covert communications and evade perimeter network monitoring?
Fleercivet 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 Fleercivet from Windows?
Manual removal of Fleercivet 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 Fleercivet infection?
Symptoms of Fleercivet 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 Fleercivet 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/fleercivet.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.