FileCatalyst can run on any port. Administrators routinely change ports to avoid conflicts, bypass firewalls, or even hide transfers. If your detection strategy is “look for port 33000,” you’re already missing the majority of traffic.
Why standard file transfer monitoring fails, and the three telltale signs of FileCatalyst in flight FileCatalyst isn’t your average file transfer protocol. Built for high-speed, long-distance, and high-latency links, it’s a favorite in media, defense, and energy sectors. But that same efficiency makes it a blind spot for many security and network teams. filecatalyst detection
On the wire: TCP segments with payload size 24 or 32 bytes, repeating with millisecond precision. Normal background noise doesn’t do that. | Layer | Tool | What to look for | |-------|------|------------------| | Flow | ntopng, ElastiFlow | Asymmetric byte ratio >100:1 + constant packet gap | | Packet | tshark | tcp.payload_length == 24 and frame.time_delta between 5–15 sec | | IDS | Suricata | Custom rule matching TLS JA3S hash (ask me for the hash list) | | Logs | Zeek | ssl log with server_name containing unusual subdomains + cipher suite 0x1301 | Pro tip: FileCatalyst often coexists with Aspera or Signiant in media networks. Don’t confuse the two — Aspera uses FASP‑UDP with a different initial window and congestion signature. 4. Two Real‑World Detection Scenarios Scenario 1 – Unauthorized server in R&D Your NDR platform alerts on a workstation sending 800 Mbps to an unknown cloud IP on UDP/443. Standard inspection shows “QUIC” — but the packet size distribution doesn’t match QUIC. You pull a PCAP and see the 24‑byte control probe. It’s FileCatalyst Direct tunneling over port 443. FileCatalyst can run on any port
A backup server initiates an outbound TCP connection to a partner IP on port 8080. The connection stays alive for 14 hours but only transfers data in three short bursts. That’s the FileCatalyst “hot folder” pattern — idle control channel, then scheduled bursts. 5. Don’t Forget The Blind Spot: UDP‑only mode In some high‑performance setups, FileCatalyst runs without TCP at all — no handshake, no keep‑alive, pure UDP data + UDP control. Most security tools assume a TCP control channel and will miss this entirely. Why standard file transfer monitoring fails, and the
Monitor for UDP flows with a stable packet‑per‑second rate above 5,000 pps for more than 10 seconds and a matching low‑rate reverse UDP flow (the control channel). Very few legitimate apps behave that way. Final thought FileCatalyst is not malicious. But undetected FileCatalyst is a policy problem, a data governance risk, and occasionally a security gap (exfiltration tools love fast UDP).
Have you found FileCatalyst hiding on non‑standard ports in your environment? Let me know below.
Beyond the Blink: How to Detect FileCatalyst Traffic on Your Network