The command port for PGP Certificate Server 2.5.0 and 2.5.1 allows remote attackers to cause a denial of service if their hostname does not have a reverse DNS entry and they connect to port 4000.
https://exchange.xforce.ibmcloud.com/vulnerabilities/4695
http://www.securityfocus.com/bid/1343
Source: Mitre, NVD
Published: 2000-06-14
Updated: 2017-12-19
Base Score: 5
Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:N/A:P
Severity: Medium
Base Score: 7.5
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Severity: High