{
  "family": "brontok",
  "sample_count": 57,
  "category": "advanced_threat",
  "description": "Worm:Win32/Brontok is a historic, highly prolific mass-mailing worm originating from Indonesia (circa 2005) that rapidly spreads via email and removable drives, utilizing aggressive self-defense mechanisms to disable antivirus software and alter system settings.<br><br><b>Understanding Brontok</b><br>To the end-user, a Brontok infection is highly disruptive. The system may suddenly reboot when attempting to run the command prompt, web browsers are forced to open specific Indonesian web pages, and the machine rapidly emails copies of the worm to everyone in the address book. For incident responders, Brontok is a classic, noisy mass-mailer. While not typically associated with data theft, its aggressive propagation and system modifications make it a severe nuisance capable of crippling network bandwidth.<br><br><b>Execution and Evasion Strategies</b><br>Brontok primarily spreads via email (spoofing the sender address to appear legitimate) or by copying itself to USB drives as an executable disguised as a folder (e.g., using a folder icon). Upon execution, Brontok copies itself to the `%AppData%` and `%SystemRoot%` directories. It establishes persistence via the Registry Run keys and scheduled tasks. It aggressively defends itself by disabling the Windows Registry Editor (`regedit.exe`), the Command Prompt (`cmd.exe`), and modifying the `HOSTS` file to block access to major antivirus vendors. It uses its own SMTP engine to harvest emails from the local drive and blast out copies of itself.<br><br><b>Indicators of Compromise & Impact</b><br>The impact is network congestion (from mass mailing) and localized system disruption. Incident responders will observe massive spikes in outbound TCP port 25 (SMTP) traffic. EDR platforms will flag multiple unauthorized registry modifications (`T1112`), specifically those disabling system utilities (`DisableRegistryTools`). The presence of oddly named executables (often resembling folder names) on USB drives or network shares is a hallmark Brontok IoC.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [],
  "faq_count": 0,
  "mitre_attack": [
    "T1091",
    "T1114.001",
    "T1566.001",
    "T1562.001",
    "T1036.005"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1566.001",
      "name": "Phishing: Spearphishing Attachment",
      "tactic": "Initial Access"
    },
    {
      "id": "T1091",
      "name": "Replication Through Removable Media",
      "tactic": "Lateral Movement"
    },
    {
      "id": "T1114.001",
      "name": "Email Collection: Local Email Collection",
      "tactic": "Collection"
    },
    {
      "id": "T1562.001",
      "name": "Impair Defenses: Disable or Modify Tools",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1036.005",
      "name": "Masquerading: Match Legitimate Name or Location",
      "tactic": "Defense Evasion"
    }
  ],
  "containment_steps": [
    "Quarantine the endpoint immediately to halt the outbound mass-mailing campaign and prevent the worm from traversing mapped network shares.",
    "Enforce egress firewall rules blocking outbound TCP port 25 from all endpoints, forcing all email traffic through authorized corporate mail relays.",
    "Disable AutoRun/AutoPlay enterprise-wide via Group Policy to halt Brontok's propagation via USB drives.",
    "Utilize offline registry editing tools or EDR to reverse the registry modifications that disabled `regedit.exe` and `cmd.exe`."
  ],
  "what_to_avoid": [
    "Do not insert a clean USB drive into the infected machine to transfer tools; Brontok will immediately infect the drive.",
    "Avoid assuming the threat is contained just by stopping the spam; the worm actively disables AV, leaving the machine vulnerable."
  ],
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ]
}