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With Autoptimize 2.7.7 released on August the 23rd and having been pushed to all sites that were still on 2.7.0-2.7.6 by the WordPress plugins team on Aug. 30th and 31th, resulting in just under one million downloads in 8 days time, it is now the moment for a small debrief of the security issues that were fixed in this version.
2.7.7 fixed two vulnerabilities, one authenticated cross-site scripting and one arbitrary file upload.

1. XSS:
   1. Problem: administrator users were able leave JavaScript in the exclusion-fields for CSS and JS optimization, leading that JS to be executed when the page was (re-)loaded.
   2. Risk: This could be abused by one administrator to execute JS against another administrator.
   3. Solution: This was fixed by applying esc_html (to become esc_attr in the next version as suggested by George Stephanis) to escape the JS-code and avoid it getting executed.
2. Arbitrary File Upload:
   1. Problem: the code that processes Critical CSS settings imports did insufficient checks to ensure no malicious files were uploaded as it lacked a user capability check, did not check file extension of to uploaded file to be zip and did not check the contents of the zip-file. It did however check for a correct nonce for that specific action.
   2. Risk: this could lead to authenticated attackers uploading PHP-files that could be executed, but that risk was very much limited by the nonce-check (which all exploits I have seen happily ignore).
   3. Solution: the code has been updated to do a capability check, to make sure the file uploaded is a zip-file and most importantly to delete any unknown file found immediately after unzipping (based on an list of known-good files).

A big thank you to the two security researchers (Erin Germ for the XSS and an anonymous whitehatter for the file upload problem) who reported these vulnerabilities in a responsible manner and to the WordPress plugin team for their invaluable help in keeping our users safe.