Backdrop CMS 1.12.x before 1.12.8 and 1.13.x before 1.13.3 allows the upload of entire-site configuration archives through the user interface or command line. It does not sufficiently check uploaded archives for invalid data, potentially allowing non-configuration scripts to be uploaded to the server. (This attack is mitigated by the attacker needing the "Synchronize, import, and export configuration" permission, a permission that only trusted administrators should be given. Other preventative measures in Backdrop CMS prevent the execution of PHP scripts, so another server-side scripting language must be accessible on the server to execute code.)

In Backdrop CMS 1.12.x before 1.12.8 and 1.13.x before 1.13.3, some menu links within the administration bar may be crafted to execute JavaScript when the administrator is logged in and uses the search functionality. (This issue is mitigated by the attacker needing permissions to create administrative menu links, such as by creating a content type or layout. Such permissions are usually restricted to trusted or administrative users.)