XWiki Platform WebJars API is a package for XWiki, a generic wiki platform. Starting with version 9.6-rc-1 and prior to versions 16.10.17, 17.4.9, and 17.10.3, a potential path traversal vulnerability allow an attacker who manages to get a malicious WebJar extension installed on the wiki to write arbitrary files. While the consequences could be severe like overriding configuration files and setting the superadmin password, the attack first requires that the attacker already has admin access to at least a subwiki to be able to install a malicious extension. Further, the attacker needs to publish a malicious extension in an extension repository that is configured in the instance. This vulnerability has been patched in XWiki 16.10.17, 17.4.9, 17.10.3, and 18.0.0RC1. XWiki is not aware of any workarounds except for being careful whom developers grant script and admin rights to.