Site opening 500 error or blank page: Operation not permitted in Unknown on line 0

Symptoms

1. After WordPress domain migration site is not available with 500 error or a white page. The same may be applicable if main domain on a subscription was renamed.

2. Wordfence plugin is installed.

3. The following errors may be found in /var/www/vhosts/example.com/logs/error.log or /var/www/vhosts/main.domain/example.com/logs/error.log:

[Fri Aug 18 13:23:39 2017] [warn] [client 203.0.113.2] mod_fcgid: stderr: PHP Warning: Unknown: open_basedir restriction in effect. File(/var/www/vhosts/example.com/httpdocs/kc080517/wordfence-waf.php) is not within the allowed path(s): (/var/www/vhosts/example.com/:/tmp/) in Unknown on line 0
[Fri Aug 18 13:23:39 2017] [warn] [client 203.0.113.2] mod_fcgid: stderr: PHP Warning: Unknown: failed to open stream: Operation not permitted in Unknown on line 0
[Fri Aug 18 13:23:39 2017] [warn] [client 203.0.113.2] mod_fcgid: stderr: PHP Warning: Unknown: open_basedir restriction in effect. File(/var/www/vhosts/example.com/httpdocs/kc080517/wordfence-waf.php) is not within the allowed path(s): (/var/www/vhosts/example.com/:/tmp/) in Unknown on line 0
[Fri Aug 18 13:23:39 2017] [warn] [client 203.0.113.2] mod_fcgid: stderr: PHP Warning: Unknown: failed to open stream: Operation not permitted in Unknown on line 0
[Fri Aug 18 13:23:39 2017] [warn] [client 203.0.113.2] mod_fcgid: stderr: PHP Fatal error: Unknown: Failed opening required '/var/www/vhosts/example.com/httpdocs/kc080517/wordfence-waf.php' (include_path='.:/opt/plesk/php/7.0/share/pear') in Unknown on line 0

Cause

Wordfence firewall configuration has not migrated properly.

Resolution

Check Wordfence firewall configuration files and correct them accordingly.