We support the latest stable release, as well as the current state of the next-minor and develop branches. Security issues for older releases are out of scope.
Found a security issue? Please disclose it responsibly. We have a team of developers listening to security@diasporafoundation.org. The PGP fingerprint is AB0D AB02 0FC5 D398 03AB 3CE1 6F70 243F 27AD 886A.