Hosts

Overview

BrowserModifier:Win32/Hosts (or simply 'Hosts file hijacker') is a generic heuristic detection for malware or adware that maliciously modifies the Windows HOSTS file to redirect web traffic, block security updates, or facilitate phishing.

What is a HOSTS Hijack?
For general consumers, a modified HOSTS file results in bizarre browsing behavior: attempting to visit google.com might redirect to a fake search engine, or attempting to visit microsoft.com simply times out. For incident responders, HOSTS hijacking is a rudimentary but highly effective DNS override technique. The Windows OS checks the local HOSTS file (C:\Windows\System32\drivers\etc\hosts) before querying external DNS servers. Malware exploits this to sinkhole security traffic or redirect banking URLs to attacker-controlled phishing infrastructure.

Infection Vectors & Threat Hunting
Malware variants (ranging from simple adware to severe banking trojans) require local Administrator privileges to modify the HOSTS file. Upon execution, the malware appends hundreds of entries to the file. Commonly, it maps AV update domains (like liveupdate.symantec.com or update.microsoft.com) to 127.0.0.1 (localhost), effectively blinding the endpoint's security software. Alternatively, it maps financial domains (chase.com) to malicious IP addresses. Threat hunters can trivially detect this by monitoring the integrity and size of the HOSTS file.

Forensic Analysis & Impact
The impact ranges from simple annoyance (adware redirection) to severe financial loss (banking phishing) and compromised security posture. Incident responders should immediately open the HOSTS file in Notepad and review the entries. EDR tools frequently trigger alerts when processes other than svchost.exe or authorized admin tools attempt to write to the \drivers\etc\ directory.

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:

• T1566: Implement email filtering, Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM), and DMARC. Conduct user phishing awareness training.

MITRE D3FEND™ Defensive Countermeasures

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

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_HOSTS_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Hosts"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "hosts" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Hosts (Trojan Generic) Execution & Triage
id: e67534b9-099c-522b-8158-644b47178a5a
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Hosts 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/hosts
- 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.trojan-generic
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1566
- attack.t1498
- attack.t1562_001
- attack.t1584
- attack.t1112
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_HOSTS_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Hosts 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 = "hosts" 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. Open the Windows HOSTS file (<code>C:\Windows\System32\drivers\etc\hosts</code>) with administrative privileges and delete all unauthorized entries.
2. Reset the HOSTS file to the Windows default (typically just comments and a localhost mapping).
3. Investigate how the malware gained administrative privileges to modify the file in the first place; a larger infection is likely present.
4. Run a full EDR sweep to identify the parent executable (often adware or a banking trojan) that orchestrated the modification.

What to Avoid

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

1. Do not assume the endpoint is clean just by fixing the HOSTS file; the malware that modified it is almost certainly still active.
2. Avoid deleting the HOSTS file entirely; while Windows can recreate it, it is best practice to restore it to the Microsoft default template.

References & External Analysis

• Search "hosts" on VirusTotal (External Analysis)
• Search "hosts" on Any.Run (Sandbox Sandbox)
• Search "hosts" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Zlob
• Adwind
• Xxybzx
• Genericrxgh
• Siscos
• Aenjaris
• Premium
• Frethog

Machine-readable

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