The Simple JWT Login WordPress plugin before 3.3.0 can be used to create new WordPress user accounts with a randomly generated password. The password is generated using the str_shuffle PHP function that "does not generate cryptographically secure values, and should not be used for cryptographic purposes" according to PHP's documentation.

The Simple JWT Login WordPress plugin before 3.2.1 does not have nonce checks when saving its settings, allowing attackers to make a logged in admin changed them. Settings such as HMAC verification secret, account registering and default user roles can be updated, which could result in site takeover.

Since "algorithm" isn't enforced in jwt.decode()in jwt-simple 0.3.0 and earlier, a malicious user could choose what algorithm is sent sent to the server. If the server is expecting RSA but is sent HMAC-SHA with RSA's public key, the server will think the public key is actually an HMAC private key. This could be used to forge any data an attacker wants.