Backup Migration before 2.1.8 Path Traversal via PclZip Restore Fallback

Backup Migration before 2.1.8 for WordPress contains a path traversal vulnerability in its PclZip restore fallback that allows an attacker to achieve arbitrary file write when an administrator restores a malicious backup archive on a server lacking the PHP zip extension. Attackers can craft a zip archive with entry names containing ".." sequences, which PclZip's extract() processes without the PCLZIP_OPT_EXTRACT_DIR_RESTRICTION option, writing a PHP file outside the intended extraction directory into the web-servable tree to achieve remote code execution.