{
  "family": "hostmodifier",
  "sample_count": 3,
  "category": "advanced_threat",
  "description": "Behavior:Win32/Hostmodifier is a specific **Heuristic Detection** that flags unauthorized modification of the Windows `hosts` file (`C:\\Windows\\System32\\drivers\\etc\\hosts`). The `hosts` file is a local text file used by the operating system to map hostnames to IP addresses, superseding DNS lookups. Malware, Adware, and Rogue Antivirus programs frequently hijack this file to redirect web traffic, block security updates, or facilitate phishing attacks.<br><br><b>Understanding Hostmodifier (DNS Hijacking)</b><br>To an end-user, a modified `hosts` file results in strange browser behavior: attempting to visit Google might redirect to an ad-filled search page, or attempting to visit a banking site might load a pixel-perfect phishing replica. For a security analyst, this alert indicates an Impair Defenses (`T1562.004`) tactic or an active attempt to manipulate the user's network routing.<br><br><b>Execution and Hijacking Mechanics</b><br>Malware typically requires Administrator privileges to modify the `hosts` file. Once executed (`T1204.002`), the malware opens the file and appends malicious entries. A common tactic is 'sinkholing' security vendors by adding entries like `127.001 update.microsoft.com` or `127.0.0.1 www.symantec.com`, which forces the local machine to route those requests to itself, effectively blocking the AV from downloading new signature definitions. Alternatively, Adware might add entries to redirect popular search engines to their own monetized portals.<br><br><b>Indicators of Compromise & Impact</b><br>The impact ranges from the inability to update security software to catastrophic credential theft via local phishing redirection. Host-based IoCs include EDR alerts monitoring changes to the `hosts` file, and manual inspection revealing long lists of unfamiliar domains mapped to `127.0.0.1` or unexpected external IP addresses. Network IoCs may involve user traffic destined for legitimate domains unexpectedly routing to unknown or malicious IP subnets.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [],
  "faq_count": 0,
  "mitre_attack": [
    "T1562.004",
    "T1566.002",
    "T1112"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1562.004",
      "name": "Impair Defenses: Disable or Modify System Firewall (Blocking AV updates)",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1566.002",
      "name": "Phishing: Spearphishing Link (Redirecting to phishing sites)",
      "tactic": "Initial Access"
    },
    {
      "id": "T1112",
      "name": "Modify Registry / System Files",
      "tactic": "Defense Evasion"
    }
  ],
  "containment_steps": [
    "Open the `C:\\Windows\\System32\\drivers\\etc\\hosts` file using a text editor (as Administrator) and review the entries.",
    "Delete any unauthorized or suspicious mappings, particularly those redirecting security vendors to `127.0.0.1` or popular sites to unknown IPs.",
    "Run a full system antimalware scan to locate and remove the executable that made the modifications in the first place.",
    "Ensure that standard users do not have local Administrator privileges, which prevents unauthorized software from altering system files."
  ],
  "what_to_avoid": [
    "Do not simply fix the `hosts` file and ignore the alert; if the malware is still running, it will re-modify the file on the next reboot.",
    "Avoid assuming a phishing alert is a false positive if the user claims they typed the URL correctly; the `hosts` file may be routing them maliciously."
  ],
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ]
}