ApostropheCMS is an open-source content management framework. Prior to version 3.5.3 of @apostrophecms/import-export, The extract() function in gzip.js constructs file-write paths using fs.createWriteStream(path.join(exportPath, header.name)). path.join() does not resolve or sanitise traversal segments such as ../. It concatenates them as-is, meaning a tar entry named ../../evil.js resolves to a path outside the intended extraction directory.

No canonical-path check is performed before the write stream is opened. This is a textbook Zip Slip vulnerability. Any user who has been granted the Global Content Modify permission, a role routinely assigned to content editors and site managers, can upload a crafted .tar.gz file through the standard CMS import UI and write attacker-controlled content to any path the Node.js process can reach on the host filesystem.

Version 3.5.3 of @apostrophecms/import-export fixes the issue.