Cross-site scripting (XSS) vulnerability in includes/startup.php in phpBB before 3.0.13 allows remote attackers to inject arbitrary web script or HTML via vectors related to "Relative Path Overwrite."
https://wiki.phpbb.com/Release_Highlights/3.0.13
https://tracker.phpbb.com/browse/PHPBB3-13531
https://security.gentoo.org/glsa/201701-25
https://github.com/phpbb/phpbb/pull/3316
https://github.com/phpbb/phpbb/commit/eaeb88133f1f028fa06f0ebe5639668436fd469e
https://exchange.xforce.ibmcloud.com/vulnerabilities/100670