In MyBB before version 1.8.24, the custom MyCode (BBCode) for the visual editor doesn't 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.

MyBB before 1.8.22 allows an open redirect on login.

In MyBB before 1.8.21, an attacker can abuse a default behavior of MySQL on many systems (that leads to truncation of strings that are too long for a database column) to create a PHP shell in the cache directory of a targeted forum via a crafted XML import, as demonstrated by truncation of aaaaaaaaaaaaaaaaaaaaaaaaaa.php.css to aaaaaaaaaaaaaaaaaaaaaaaaaa.php with a 30-character limit, aka theme import stylesheet name RCE.

In MyBB before 1.8.21, an attacker can exploit a parsing flaw in the Private Message / Post renderer that leads to [video] BBCode persistent XSS to take over any forum account, aka a nested video MyCode issue.

A reflected XSS vulnerability in index.php in MyBB 1.8.x through 1.8.19 allows remote attackers to inject JavaScript via the 'upsetting[bburl]' parameter.

A reflected XSS vulnerability in the ModCP Profile Editor in MyBB before 1.8.20 allows remote attackers to inject JavaScript via the 'username' parameter.

A Persistent XSS issue was discovered in the Visual Editor in MyBB before 1.8.19 via a Video MyCode.

MyBB Group MyBB contains a Incorrect Access Control vulnerability in Private forums that can result in Users can view posts from private forums without having the password. This attack appear to be exploitable via Subscribe to a forum through IDOR. This vulnerability appears to have been fixed in 1.8.15.

MyBB Group MyBB contains a File Inclusion vulnerability in Admin panel (Tools and Maintenance -> Task Manager -> Add New Task) that can result in Allows Local File Inclusion on modern PHP versions and Remote File Inclusion on ancient PHP versions. This attack appear to be exploitable via Must have access to admin panel. This vulnerability appears to have been fixed in 1.8.15.

MyBB 1.8.14 is not checking for a valid CSRF token, leading to arbitrary deletion of user accounts.

MyBB 1.8.14 has XSS via the Title or Description field on the Edit Forum screen.

SQL injection vulnerability in userbarsettings.php in the Userbar plugin 2.2 for MyBB Forum allows remote attackers to execute arbitrary SQL commands via the image2 parameter.