{
  "family": "sasfis",
  "sample_count": 5,
  "category": "trojan",
  "description": "TrojanDownloader:Win32/Sasfis is a prevalent, highly active botnet component and downloader trojan. It is primarily utilized by cybercriminal syndicates as a 'first-stage' loader. Once a machine is infected with Sasfis, it effectively becomes a node in a vast botnet, quietly waiting for commands from a C2 server to download and execute secondary, more damaging payloads, typically massive spamming engines or aggressive banking trojans.<br><br><b>Understanding the Sasfis Downloader</b><br>To an end-user, Sasfis operates entirely in the background; they may only notice a slight decrease in network performance. For an enterprise, a Sasfis detection is a major red flag indicating a total failure of email filtering and endpoint protection, and strongly suggests that the machine has already downloaded subsequent malware families.<br><br><b>Execution and Payload Delivery</b><br>Sasfis is notoriously spread via massive, generic malspam campaigns (e.g., fake invoices, shipping alerts) containing weaponized ZIP files or Office macros (`T1566.001`). Upon execution, the malware copies itself to the Windows `%AppData%` or `%System32%` directory and creates a Registry Run key for persistence (`T1547.001`). It then initiates a beacon to its C2 infrastructure using standard HTTP/HTTPS over port 80/443, making it difficult to distinguish from normal web traffic (`T1071.001`). The C2 server responds with encrypted URLs pointing to secondary payloads. Sasfis downloads these payloads, decrypts them in memory, and injects them into legitimate processes (`T1055`) to evade detection.<br><br><b>Indicators of Compromise & Impact</b><br>The impact is a guaranteed secondary infection. Host-based IoCs include EDR alerts for unknown executables in `AppData` initiating outbound HTTP GET requests to known malicious domains or raw IP addresses. Network IoCs include consistent, high-frequency beaconing traffic. Security analysts should closely examine process execution logs to see what child processes the Sasfis executable spawned after its initial network connection.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [],
  "faq_count": 0,
  "mitre_attack": [
    "T1547.001",
    "T1566.001",
    "T1071.001",
    "T1105"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1105",
      "name": "Ingress Tool Transfer (Downloading secondary payloads)",
      "tactic": "Command and Control"
    },
    {
      "id": "T1071.001",
      "name": "Application Layer Protocol: Web Protocols (C2 Beaconing)",
      "tactic": "Command and Control"
    },
    {
      "id": "T1547.001",
      "name": "Boot or Logon Autostart Execution: Registry Run Keys",
      "tactic": "Persistence"
    },
    {
      "id": "T1566.001",
      "name": "Phishing: Spearphishing Attachment",
      "tactic": "Initial Access"
    }
  ],
  "containment_steps": [
    "Immediately isolate the infected endpoint from the network to sever the C2 connection and halt the downloading of secondary payloads.",
    "Assume the machine is fully compromised; wiping and reimaging the system is highly recommended over attempting to manually clean a botnet node.",
    "Analyze proxy and DNS logs to identify the C2 domains Sasfis contacted, and block them at the network perimeter to protect other endpoints.",
    "If manual cleaning is attempted, heavily scrutinize the registry Run keys and Scheduled Tasks for persistence hooks."
  ],
  "what_to_avoid": [
    "Do not assume the threat is mitigated if only the Sasfis dropper is quarantined; the secondary payloads it downloaded will likely still be running.",
    "Avoid relying on standard, offline AV scans, as the payloads are often heavily packed and injected directly into the memory of legitimate processes."
  ],
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ]
}