An CSRF issue was discovered in the JN-Jones MyBB-2FA plugin through 2014-11-05 for MyBB. An attacker can forge a request to an installed mybb2fa plugin to control its state via usercp.php?action=mybb2fa&do=deactivate (or usercp.php?action=mybb2fa&do=activate). A deactivate operation lowers the security of the targeted account by disabling two factor authentication.

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.

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.

MyBB 1.8.19 has XSS in the resetpassword function.

MyBB 1.8.19 allows remote attackers to obtain sensitive information because it discloses the username upon receiving a password-reset request that lacks the code parameter.

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.

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.

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.