# tcp\_123 **Explanation** The tcp\_123 NDM flags interactive connections leaving the customer's network to destinations on TCP port 123. The Network Time Protocol service uses UDP port 123, but does not use TCP. In some cases malware will connect out to servers on TCP port 123 in order to evade detection. You may also see inbound TCP connections sourced from port 123 because this can evade poorly written firewall rules. **What to Look For** The use of TCP port 123 is almost never expected or authorized. Hosts initiating these connections should be checked to make sure that they are not infected with malware. **Related MITRE ATT\&CK Categories** [Command and Control: Protocol Tunneling, Technique T1572 - Enterprise](https://attack.mitre.org/techniques/T1572) --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.fusion.vectra.ai/detection-models/library/post-compromise/tcp_123.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.