FTP servers can allow an attacker to connect to arbitrary ports on machines other than the FTP client, aka FTP bounce.
https://exchange.xforce.ibmcloud.com/vulnerabilities/CVE-1999-0017
Source: Mitre, NVD
Published: 1997-12-10
Updated: 2022-08-17
Base Score: 7.5
Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:P
Severity: High
Base Score: 9.1
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Severity: Critical