TL;DR: If you are using node-jsonwebtoken, pyjwt, namshi/jose, php-jwt or jsjwt with asymmetric keys (RS256, RS384, RS512, ES256, ES384, ES512) please update to the latest version. See jwt.io for more information on the vulnerable libraries. (Updated 2015-04-20) This is a guest post from Tim McLean, who is a member of the Auth0 Security Researcher Hall of Fame. Tim normally blogs at www.timmclean.