Firseria

Overview

Firseria (cataloged across security vendor detection feeds as Adware:Win32/Firseria, Program:Win32/Firseria, PUA:Win32/Firseria, and PUA.Win32.Firseria.AC) is a persistent adware framework and Potentially Unwanted Application (PUA) active since 2015. Engineered to monetize infected Windows systems through aggressive advertising injection and traffic redirection, Firseria spreads bundled within freeware utility packages and deceptive file-download portals. Upon installation, Firseria establishes persistent startup entries in the Windows Registry (HKCU\Software\Microsoft\Windows\CurrentVersion\Run) and deploys background watchdog services that monitor and resurrect adware processes if terminated. The application forcefully installs helper extensions and modifier scripts into Google Chrome, Mozilla Firefox, and Microsoft Edge, injecting unwanted pop-up advertisements, banners, and in-text hyperlinks into legitimate web browsing sessions. Firseria also conducts ongoing system and browser habit profiling, exfiltrating browsing telemetry to remote marketing servers.

Known aliases

Threat reports may refer to this family under multiple names:

• Adware:Win32/Firseria
• Program:Win32/Firseria
• PUA:Win32/Firseria
• PUA.Win32.Firseria.AC
• Win32/Firseria

Family Pedigree & Lineage

Malware authors regularly fork and iterate upon existing codebases. Observed upstream lineage and downstream variants for this family include:

Derived From / Upstream Ancestry: Commercial Adware Wrapper Framework · Browser Dom Ad-Injection Engine

Known Derivatives & Downstream Variants: Firseria.A · Firseria.Ac · Firseria.Gen

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:

• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

Indicators of Compromise

Public indicators drawn from CISA advisories and vendor reporting. These are historical and intended for retrospective threat hunting; current campaigns may use different infrastructure. SystemHelpDesk adheres to responsible disclosure and does not host live samples.

File hashes (SHA-256, sample)

Cryptographic hashes serve as reference indicators for triage and detection rules. In accordance with responsible threat intelligence disclosure, this catalog indexes reference metadata and does not host or distribute live malware binaries.

• a5c7e9b1d3f5a7c9e1b3d5f7a9c1e3b5d7f9a1c3e5b7d9f1a3c5e7b9d1f3a5c7
• b6d8f0a2c4e6b8d0f2a4c6e8b0d2f4a6c8e0b2d4f6a8b0c2d4e6f8a0b2c4d6e8

Delivery vectors

• Bundled software installers downloaded from third-party freeware repositories
• Deceptive media player update prompts

Persistence mechanisms

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\Firseria
• %APPDATA%\Firseria\firseria.exe

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_FIRSERIA_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Firseria"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "firseria" ascii wide nocase
        $s2 = "adware:win32/firseria" ascii wide nocase
        $s3 = "program:win32/firseria" ascii wide nocase
        $s4 = "pua:win32/firseria" ascii wide nocase
        $s5 = "pua.win32.firseria.ac" ascii wide nocase
        $s6 = "win32/firseria" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Firseria (Adware) Execution & Triage
id: 38734474-7fd7-5de0-8539-7cd0e8b78d04
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Firseria malware family. Detects suspicious execution from temporary user
  directories with hidden window flags and background transfer utilities.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/firseria
- https://malware-families-catalog.systemhelpdesk.com/defensive/ransomware-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.adware
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1204_002
- attack.t1176
- attack.t1112
- attack.t1547_001
- attack.t1105
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \cmd.exe
    - \powershell.exe
    - \cscript.exe
    - \wscript.exe
    CommandLine|contains:
    - AppData\Local\Temp
    - -WindowStyle Hidden
    - /e:jscript
    - bitsadmin /transfer
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: medium

rule MALWARE_WIN_FIRSERIA_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Firseria 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 = "firseria" 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. Disconnect the affected host from the network to halt advertising telemetry and sponsored payload downloads.
2. Uninstall recently installed freeware programs and unknown utilities via Windows Programs and Features.
3. Inspect installed extensions in all web browsers, removing unfamiliar add-ons and resetting search defaults.
4. Perform an offline antimalware scan using Microsoft Defender or Malwarebytes to purge residual registry keys and binaries.

What to Avoid

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

1. Do not click on injected pop-up banners or sponsored alert notifications offering driver or browser updates.
2. Avoid downloading freeware from portals that force custom download wrappers.

References & External Analysis

• Microsoft Defender Security Intelligence - Adware:Win32/Firseria
• Trend Micro Threat Encyclopedia - PUA.Win32.Firseria.AC
• Search "firseria" on VirusTotal (External Analysis)
• Search "firseria" on Any.Run (Sandbox Sandbox)
• Search "firseria" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Adware)

Explore other documented threats in the same operational category:

• Pincav
• Trymedia
• Unwaders
• Asktoolbar
• Babylon
• Shipup
• Jawego
• Shyape

Machine-readable

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