Matrix Synapse before 0.28.1 is prone to a denial of service flaw where malicious events injected with depth = 2^63 - 1 render rooms unusable, related to federation/federation_base.py and handlers/message.py, as exploited in the wild in April 2018.Referenceshttps://matrix.org/blog/2018/05/01/security-update-synapse-0-28-1/https://github.com/matrix-org/synapse/commit/33f469ba19586bbafa0cf2c7d7c35463bdab87eb
