{
  "family": "kuluoz",
  "sample_count": 22,
  "category": "ransomware",
  "description": "Trojan:Win32/Kuluoz (also known as Asprox) is a massive, highly resilient spam botnet and trojan downloader. Initially infamous for turning infected machines into spam-sending zombies, it evolved into a highly lucrative Initial Access Broker, using its massive infection base to download and install secondary payloads like ransomware (CryptoWall) and banking trojans (Zbot) for affiliate threat actors.<br><br><b>Understanding Kuluoz</b><br>To the victim, a Kuluoz infection might cause system slowdowns or network latency as the machine sends out thousands of spam emails in the background. For a security analyst, Kuluoz is a tier-one threat. If Kuluoz is on the network, it means the perimeter has been breached, the endpoint is actively participating in global malspam campaigns, and it is highly likely that a devastating secondary payload (like ransomware) is imminent.<br><br><b>Execution, Spamming, and Payload Delivery</b><br>Kuluoz is primarily distributed via highly convincing spearphishing campaigns (fake FedEx, UPS, or court subpoenas) containing weaponized ZIP files (`T1566.001`). Upon execution, it injects its core modules into `svchost.exe` (`T1055`) to hide its activity. It reaches out to a decentralized C2 infrastructure, often utilizing fast-flux DNS or DGA (Domain Generation Algorithms) (`T1568.002`), making its infrastructure highly resilient against takedowns. It receives a list of email addresses and spam templates, turning the endpoint into an SMTP relay (`T1583.003`). Crucially, the C2 server can issue a command to download and execute secondary EXEs (`T1105`), monetizing the infection by installing other malware.<br><br><b>Indicators of Compromise & Impact</b><br>The impact is severe network reputation damage (as the corporate IP is blacklisted for spamming) and high risk of ransomware deployment. Network logs will show massive amounts of outbound SMTP (port 25) traffic from a standard user workstation, which is highly anomalous. EDR platforms should alert on `svchost.exe` attempting to resolve DGA domains or dropping secondary unsigned executables.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [],
  "faq_count": 0,
  "mitre_attack": [
    "T1105",
    "T1055",
    "T1568.002",
    "T1583.003",
    "T1566.001"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1583.003",
      "name": "Acquire Infrastructure: Botnet",
      "tactic": "Resource Development"
    },
    {
      "id": "T1105",
      "name": "Ingress Tool Transfer",
      "tactic": "Command and Control"
    },
    {
      "id": "T1568.002",
      "name": "Dynamic Resolution: Domain Generation Algorithms",
      "tactic": "Command and Control"
    },
    {
      "id": "T1055",
      "name": "Process Injection",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1566.001",
      "name": "Phishing: Spearphishing Attachment",
      "tactic": "Initial Access"
    }
  ],
  "containment_steps": [
    "Instantly isolate the endpoint from the network to halt the outbound spam wave and prevent the downloading of secondary ransomware.",
    "Check corporate firewall and email gateway logs to determine how much spam was successfully sent and request delisting from IP reputation blocklists if necessary.",
    "Capture a forensic memory image (RAM dump) to extract the injected Kuluoz modules from svchost.exe and identify the DGA seed.",
    "Assume total compromise; perform a clean OS rebuild, as Kuluoz is known to act as a downloader for multiple other advanced threats."
  ],
  "what_to_avoid": [
    "Do not treat a Kuluoz alert as just a 'spam' issue; it is a critical indicator of compromise that frequently precedes ransomware.",
    "Avoid relying solely on static IP blocking; Kuluoz uses highly dynamic infrastructure (fast-flux and DGA) to evade simple blocklists."
  ],
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ]
}