UDP Port 123 – ntp

Network Time Protocol. Provides time synch between computers and network systems. Assists in database mgmt, auth schemes, and audit/logging accuracy. Security Concerns: It provides both info and an avenue of attack for intruders. Info gathered can include: system uptime, time since reset, time server pkt, I/O, & memory statistics, and ntp peer list. Further, if a host is susceptible to time altering via ntp, an attacker can: 1) Run replay attacks, using captured OTP and Kerberos tickets before they expire. 2) Stop security-related cron jobs from running or cause them to run at incorrect times. 3) Make system and audit logs unreliable, since time is alterable.

Port 123 carries NTP time synchronization, including the Windows Time service. Community reports note that blocking it prevents clock sync, and that Windows domain servers can drop communication with machines whose clocks drift; administrators typically allow at least one trusted NTP source through the firewall.

About UDP Port 123

Port 123 is registered with the Internet Assigned Numbers Authority (IANA) for ntp. The IANA description reads: ‘Network Time Protocol’.

Data Sources

This information is compiled from: IANA Service Name and Transport Protocol Port Number Registry.