Joomla!: [20190502] - Core - By-passing protection of Phar Stream Wrapper Interceptor

In Joomla 3.9.3, the vulnerability of insecure deserialization when executing Phar archives was addressed by removing the known attack vector in the Joomla core. In order to intercept file invocations like file_exists or stat on compromised Phar archives the base name has to be determined and checked before allowing to be handled by PHP Phar stream handling. The used implementation however is vulnerable to path traversal leading to scenarios where the Phar archive to be assessed is not the actual (compromised) file.