TCP Port 991 – nas

About TCP Port 991

The Internet Assigned Numbers Authority (IANA) registers port 991 for nas. The IANA description reads: ‘Netnews Administration System’. This port appears in 3 IDS rules and does not have notable malware activity indicators in our data.

IDS Rule References

3 IDS / security rules reference TCP port 991. 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 1): bad-unknown (3).

Sample rule descriptions for TCP port 991:

• ET EXPLOIT Possible OpenSSL HeartBleed Large HeartBeat Response from Common SSL Port (Outbound from Server)
• ET EXPLOIT Possible OpenSSL HeartBleed Large HeartBeat Response from Common SSL Port (Outbound from Client)
• ET EXPLOIT FREAK Weak Export Suite From Server (CVE-2015-0204)

Data Sources

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