PEAR Archive_Tar allows an unserialization attack because phar: is blocked but PHAR: is not blocked. PEAR stands for PHP Extension and Application Repository and it is an open-source framework and distribution system for reusable PHP components with known usage in third-party products such as Drupal Core and Red Hat Linux.
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CWE-74
https://pear.php.net/bugs/bug.php?id=27002, https://www.drupal.org/sa-core-2020-013, https://access.redhat.com/security/cve/cve-2020-28949