MyBB Improper Neutralization of Input During Web Page Generation (Cross-site Scripting) Vulnerability - CVE-2020-15139

In MyBB before version 1.8.24 the custom MyCode (BBCode) for the visual editor doesn39t escape input properly when rendering HTML resulting in a DOM-based XSS vulnerability. The weakness can be exploited by pointing a victim to a page where the visual editor is active (e.g. as a post or Private Message) and operates on a maliciously crafted MyCode message. This may occur on pages where message content is pre-filled using a GET/POST parameter or on reply pages where a previously saved malicious message is quoted. After upgrading MyBB to 1.8.24 make sure to update the version attribute in the codebuttons template for non-default themes to serve the latest version of the patched jscripts/bbcodes_sceditor.js file.