The vulnerability stems from insufficient path validation during ZIP extraction. The GitHub commit 32c9009 introduced the 'isBelow()' check in both extractCustom() and extractNative() methods, confirming these functions previously lacked path traversal safeguards. Before the patch, they concatenated user-controlled filenames (from ZIP entries) with the destination path without resolving absolute paths or checking for directory escapes. This allowed malicious ZIP entries with '../' sequences to write files outside the target directory.