An issue was discovered in inc/class_feedgeneration.php in MyBB 1.8.17. On the forum RSS Syndication page, one can generate a URL such as http://localhost/syndication.php?fid=&type=atom1.0&limit=15. The thread titles (within title elements of the generated XML documents) aren't sanitized, leading to XSS.

The New Threads plugin before 1.2 for MyBB has XSS.

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 1.8.15, when accessed with Microsoft Edge, mishandles 'target="_blank" rel="noopener"' in A elements, which makes it easier for remote attackers to conduct redirection attacks.

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.

The installer in MyBB before 1.8.13 has XSS.

The installer in MyBB before 1.8.13 allows remote attackers to execute arbitrary code by writing to the configuration file.

In MyBB before 1.8.11, the smilie module allows Directory Traversal via the pathfolder parameter.