Description:
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Tested on PHP 7.2.10, there might be memory leak while using ftp_login function and maybe other functions with FTPS (FTP over SSL).

To reproduce the memory leak, you should open a connection to a FTP server with SSL and then try to login with ftp_login. The test script uses a public FTP that supports SSL for testing but I could reproduce with other FTP servers with valid or invalid credentials.

I also provided another test script (for Unix/Linux) that uses an infinite loop to have a better view of the memory increasing at every turn just after ftp_login is called, see:

https://gist.githubusercontent.com/guenard/6fca07e5c99f959de42dbed67628acf9/raw/b1c97d732a3e8acf249cf415e067b7f0e94075ae/lopp-ftp-with-ssl-login-memory-leak.php

The closest issue I found was https://bugs.php.net/bug.php?id=65228 but it looks like the patch has made it from PHP 5.5.x to PHP 7.2.x.

Test script:
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<?php
$conn = @ftp_ssl_connect('test.rebex.net', 21);
@ftp_login($conn, '', '');
@ftp_close($conn);

Expected result:
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No memory leak.

Actual result:
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==9752== LEAK SUMMARY:
==9752==    definitely lost: 947 bytes in 6 blocks
==9752==    indirectly lost: 15,057 bytes in 219 blocks
==9752==      possibly lost: 0 bytes in 0 blocks
==9752==    still reachable: 4,267 bytes in 26 blocks
==9752==         suppressed: 0 bytes in 0 blocks