TCP Port 873 – rsync

About TCP Port 873

Port 873 is registered with the Internet Assigned Numbers Authority (IANA) for rsync. The IANA description reads: ‘rsync’. This port appears in 8 IDS rules and does not have notable malware activity indicators in our data.

IDS Rule References

8 IDS / security rules reference TCP port 873. Treat that number as context, not a danger score. Many detection rules are written against groups of ports rather than one service, web ports especially, so common web alternate ports inherit large counts while genuinely sensitive services can show few rules or none. Presence in IDS rules does not mean traffic on this port is malicious.

Rule categories (top 4): attempted-admin (4), misc-activity (2), attempted-user (1), string-detect (1).

Sample rule descriptions for TCP port 873:

• SERVER-OTHER rsyncd module list access
• SERVER-OTHER rsync backup-dir directory traversal attempt
• ET EXPLOIT F5 BIG-IP rsync cmi access attempt
• ET EXPLOIT F5 BIG-IP rsync cmi authorized_keys access attempt
• ET EXPLOIT F5 BIG-IP rsync cmi authorized_keys successful exfiltration

Data Sources

This information is compiled from: IANA Service Name and Transport Protocol Port Number Registry, Emerging Threats Open Ruleset (BSD 2-Clause / GPLv2 per SID range), and Snort Community Rules (GPLv2).